Using grid inverters without solar/wind

Delly · August 2013

Hi, I'm a student and currently working on a project which is about trying to reduce the peak load at days through energy saved in batteries during night.
Where I live is pretty cold and the sun isn't much to brag about since I live far in north. I've been researching this for 2 months now and have come to some solution and would like to have some help clarifying my concerns. The picture attached is from an ebay dealer and is pretty much what I'm trying to do except for 2 parts which are the AC and battery charger. I want to be able to use the stored energy during night(when el.price is low) and use it myself at morning when the el.price is high or even sell it back should I wish so. I'm always connected to the 220-230vac grid.

So my problem here is:
1) What sort of grid tie inverter do I need to be able to do the details described above. Ive read on this forum(link underneath picture, reply by Bill) that connecting heavy load on terminal load of cc is unwise. If I connect the inverter to the batteries directly, the batteries will run flat without any control, right? So how do people normally connect the AC inverter?

2) I'm thinking of using a power supply instead of a battery charger. Mostly because I think there might be a crash if 2 units try to regulate the battery voltage. Do charge controllers support power supplies? Power supplies deliver constant voltage when the load increases, while PV arrays do not. The cc will try to regulate the voltage to maximize the power gained from PV in to the batteries. I'm sensing a crash will occur here.

3) If there is no current limit from the batteries to the grid tie inverter the grid tie inverter will overheat and start smoking. I found this video on youtube (3:46-4:30) which explains my 3rd concern: http://www.youtube.com/watch?v=vH4pIVNEV6Y. Doesn't the cc pretty much do this for me?

4) I'm thinking that since there is no sun involved a pwm cc is better suited. Am I correct?

5) How do I size cc, power supply and (grid tie) inverter based on the following criteria while overcoming the problems above?

- 12v(could be 24 or 48 ), 150Ah @ 12v, 1800wh (including 50% discharge rate and 80% battery efficiency)
- 220-230VAC
- 7.5 hours charging at night.
- 1800/7.5 = 240wh of charging.

-> 300w inverter (with sell back option)?
-> Power supply/battery charger?
-> Charge controller?

Note that I'll be testing this as a prototype which means I'm almost certain I'll use uncertified Asian products as a concept of proof for my school. Help is very much appreciated!

Edit: If this project succeeds, there are plans to test it out on 20 homes each with 2-5kwh battery system depending on the price. When this do happen, build quality and safety will be priority #1.

Thanks in advance,
Delly

Attachment not found.
link: here

solarix · August 2013

Re: Using grid inverters without solar/wind

The last time I thought about doing this, my conclusion was that the costs of batteries were higher than the savings realized. And that was using a spare inverter I already have. This was using energy prices where I'm at which is 6 cents off peak, 17 cents on peak.
My conclusion, (from years ago from working in the airline efficiency game) is that you can't economize your way to success. You need some big advantage like Coke selling sugar water, or the Casino's with their house advantage, or your average utility burning coal (or hey - maybe solar PV with an unlimited, clean energy source). To make it on the Good Ship America, with its high costs of overhead and taxation, you gotta have some real profit margin - not just spend a ton to shave a few pennies off your expenses.

Cariboocoot · August 2013

Re: Using grid inverters without solar/wind

Welcome to the forum.

Well your picture shows a solar charge controller, not an inverter, and that would not be used here.

What you're talking about I believe is "time shifting"; Charging batteries from the grid when rates are low and then using the batteries to power an inverter to run loads when rates are high. There is rarely any economic advantage to this as the cost of the equipment (including pro-rating of the batteries) is pretty high compared to the difference in cost of the grid power at the two rates.

Otherwise, you would not use a grid-tie inverter at all as you would not be selling back to the grid so there would be no need for that function. A battery-based inverter would be used (this could include hybrid GT inverters such as the Xantrex XW series). If you buy a good one it has the charger and transfer switch built-in.

Believe it or not, this isn't an uncommon set-up in some areas where the grid is unreliable.

It works like this:
Grid connected to AC IN of the inverter-charger. When grid is present, batteries are charged by the grid. Loads are powered by the grid. When grid goes down, inverter switches seamlessly to supply power to loads (on AC OUT of the inverter) from batteries.

For time-shifting you need to add a circuit to activate a separate relay and connect the grid to AC IN at the appropriate time. This is usually done by adapting the automatic generator start control of the higher-end inverters.

Storing low-priced grid energy in batteries and selling it back would required one of he hybrid GT inverters, but as I said would not be practical and may even be illegal. At the moment several utilities are having fits over the possibility of people doing this and have stopped the installation of this type of inverter. Without the co-operation and permission of the utility any such GT install would be illegal, and would not necessarily work; wrong meter/programming and you get charged for what you produce instead of credited.

On the whole it isn't worth the effort. You'd need a really big price difference between minimum and maximum grid price per kW hour to make it worthwhile.

BTW, I'm not surprised about #3; powering a standard GTI from batteries is a definite no-no. They are meant to be powered by solar panels alone, not the unlimited current potential of a battery bank.

You will not find a 300 Watt inverter suitable to this task either.

BB. · August 2013

Re: Using grid inverters without solar/wind

Delly wrote: »

Hi, I'm a student and currently working on a project which is about trying to reduce the peak load at days through energy saved in batteries during night.
Where I live is pretty cold and the sun isn't much to brag about since I live far in north. I've been researching this for 2 months now and have come to some solution and would like to have some help clarifying my concerns. The picture attached is from an ebay dealer and is pretty much what I'm trying to do except for 2 parts which are the AC and battery charger. I want to be able to use the stored energy during night(when el.price is low) and use it myself at morning when the el.price is high or even sell it back should I wish so. I'm always connected to the 220-230vac grid.

This is known as "load shifting" (shifting the energy use to different times to take advantages of time of use plans).

In some countries (Eastern Europe region for a few), it has been "illegal" to connect any sort of battery powered inverter that allowed a person to buy power at night and sell it during the day.

And we are just now in California seeing a utility outlawing these types of connections too... In one case, the utility person was saying because it is potentially unsafe (it is not--Hybrid inverters have been in place and being used for many years without problems). And in another the utility was saying it was "illegal" because it was not Solar Renewable Energy power--But a person could buy from the grid at night (non-RE power) and sell during the day. And their term was that batteries are non-RE generators (a misunderstanding, the non-Solar RE buy/selling of power is the "reason").

The actual issue is that in some places, Grid Tied connected homes are accounting for more than 1% of the installed generation capacity. And the "lost utility profits" are becoming noticeable on the bottom line (and possibly utility engineering impacts too). Personally, I do believe that Solar RE is currently setup such that it will cost the utility and other non-solar customers money and the complaints are real--But in any case, it is probably heading for the courts now (lots of customers with systems installed and waiting for final inspections and now being turned down).

So my problem here is:
1) What sort of grid tie inverter do I need to be able to do the details described above. Ive read on this forum(link underneath picture, reply by Bill) that connecting heavy load on terminal load of cc is unwise. If I connect the inverter to the batteries directly, the batteries will run flat without any control, right? So how do people normally connect the AC inverter?

Most of the Hybrid Inverters (capable of Grid Tied and Off Grid operation with a battery bank--And usually capable for selling power back to the utility)--Are pretty programmable. And you can set both the minimum "sell voltage" and another shutdown point if the battery gets too low.

For example--On a 48 volt battery bank. ~50.8 is battery "resting" fully charged. ~52 volts "float charging", and ~58-61 volts charging very hard. Also note that lead acid batteries are fairly temperature sensitive... Roughly -0.005 volts per degree C per cell (-5mV per C per Cell). So if you do anything with Lead Acid batteries, you usually need to temperature compensate them... And note that fast charging can result in thermal run-away (lots of charging current, batteries get hot, charging voltage falls, charger thinks more charging current needed, batteries get hotter, etc.). There are battery fires even in commercial battery systems because of maintenance and operation issues--And the occasional factory/unknown failures.

A standard Solar RE configuration would "turn on" selling power to the grid at ~52 volts (after battery bank is fully charged--as determined by the hybrid inverter logic). As the solar array (or wind, water turbines, etc.) try to pull the battery voltage over 52 volts, the hybrid inverter behaves like a "dump load" and shunts the excess charging current to the grid (and spinning the utility meter backwards--if the Hybrid inverter exceeds the homes local power needs).

You can program the GT inverter to (for example) not allow the battery bank go below ~46-48 volts to keep the battery bank from going below ~50% state of charge. However, using voltage to determine the state of charge of the battery bank is less than ideal--Voltage itself is not a very accurate representation of battery bank capacity.

BB. wrote: »

New poster "leaf" has a really nice set of charts that compare battery voltage against different rates of discharging and charging (as well as resting voltage readings).

I don't quite a agree with the resting voltage line (I think the voltage is a bit low)--But it shows how to estimate a battery's state of charge while operating.

Note, where the charts "flatten out"--the room for error estimating state of charge is pretty high.

-Bill

End of part one

BB. · August 2013

Re: Using grid inverters without solar/wind

Begin part two

You can go a bit better by using a Battery Monitor (like this one from Victron). A few monitors out there have a programmable output/alarm contact that you can set to "turn off" at 50% State of charge and turn back on at 80% State of charge (for example)--And more accurately control battery state of charge/use as a "hard limit" for discharging.

A battery monitor puts a shunt (a precision high power resistor) in the battery negative cable and measures the Amps*Hours going into and out of the battery bank to estimate the present battery state of charge. They work well, but can drift over days/weeks of use--So you have to keep an eye on them and ensure that the Battery Monitors are "reset" to 100% by fully charging the bank every 2-10 days.

2) I'm thinking of using a power supply instead of a battery charger. Mostly because I think there might be a crash if 2 units try to regulate the battery voltage. Do charge controllers support power supplies? Power supplies deliver constant voltage when the load increases, while PV arrays do not. The cc will try to regulate the voltage to maximize the power gained from PV in to the batteries. I'm sensing a crash will occur here.

In general, you can parallel multiple battery chargers. Wire each charger directly to the battery main bus connections (don't use one set of cables from the battery to charger A to charger B to charger C--Daisy Chain wiring--The interaction of chargers and voltage drop on the same cabling can confuse the chargers).

For solar charging, there are two main classes of charge controllers. One is PWM--simply an "on/off" switch between the array and the battery bank. As the the battery bank becomes full, the PWM controller simply turns off a fraction of a second every second (can be seconds, or 100's of times second). As the battery aproaches full charge, the PWM controller spends more time "off" than "on" (pulse width modulation).

The other major class is MPPT (maximum power point tracking). This controller finds the solution for the equation of Pmax=Vmp*Imp (mp=Maximum Power). Solar panels are current devices and there is a power peak based on array configuration and solar array temperature. The MPPT controller is (usually) a buck mode type switching power supply (computer controlled) where it takes high voltage/low current of the array and "efficiently down converts" to low voltage/high current for the battery bank.

MPPT controllers are advertized because the can got ~10-15% more power from a solar array because they can find Power Max and in subfreezing weather, you can get more power from a solar array vs a PWM type controller.

And you can, but it is usually not worth the cost of a MPPT controller (~4x the cost of a PWM controller).

Where MPPT are very useful is 1) large/cheap solar panels these days are "non-standard" voltages for charging battery banks and a MPPT controller will down convert high Vmp to lower Vbatt-charging efficiently. It is easy to loose 50% or more power with "Grid Tied" marketed solar panels connected to a 12/24/48 volt battery bank.

The other use is for larger array (typically over 800 watts). You can run Vmp-array at 100 volts Vmp (or even higher with some controllers) and use much smaller wire (and/or have the array some distance from the battery shed/charge controller). It is much easier to ship 100 VDC power a hundred yards than it is to ship the same Wattage (power) at 17.5 volts and using a PWM charge controller (you would pay lots of money for copper or aluminum wiring to keep the voltage drop low with a low voltage/high current solar array).

3) If there is no current limit from the batteries to the grid tie inverter the grid tie inverter will overheat and start smoking. I found this video on youtube (3:46-4:30) which explains my 3rd concern: http://www.youtube.com/watch?v=vH4pIVNEV6Y. Doesn't the cc pretty much do this for me?

A properly designed DC power system (battery, wiring, equipment) will be safe. That was a "cheap" GT inverter and they are known for overheating/failing (and being unreliable) if you operate them even at rated power. A good hybrid or pure GT inverter (no battery bank used) will not overheat.

The video is using a "boost type switch mode" power supply to "adjust" the voltage input to the GT inverter. This is not how a larger hybrid system would be configured. The boost converter is about 90% efficiency--So they will get hot. If you have a 5kW GT/hybrid system, you would "wasting" about 500 watts at the boost converter plus another 5-10% at the GT inverter. A good hybrid inverter should be around 94% efficient (vs the ~82% efficiency of the video setup).

Such a setup would not be recommended and should be unneeded with a hybrid inverter system designed for load/power shifting.

4) I'm thinking that since there is no sun involved a pwm cc is better suited. Am I correct?

I am not quite sure what your question is... PWM is a common engineering "tool" and is not a "thing" in itself. In your DC power supply, you probably have a PWM stage for controlling power transfer/output voltage+current characteristics.

Using a Power Supply vs a Battery charger--Yes it can be done, but there are issues. You are generally better off using a "real battery charger" as not all Power Supplies are capable of charging batteries (lots of possible issues).

Note that most "hybrid" capable AC inverters include their own Battery Chargers too--And these battery chargers are usually pretty high-tech/configurable. Plus a true Hybrid inverter can give you "UPS" type function (uninterruptable power supply) type function (backup AC power for the home if utility power fails). Some even have AC2 input and automatic generator controls.

For Solar power systems, in general for smaller systems (~400 watts or less), PWM solar charge controllers are "good enough" for many smaller installations. For larger systems (~800 watts or larger solar array), a MPPT charge controller is usually better for multiple reasons (less copper wire costs for array wiring, better logging/control in high end MPPT controllers, etc.).

5) How do I size cc, power supply and (grid tie) inverter based on the following criteria while overcoming the problems above?

- 12v(could be 24 or 48 ), 150Ah @ 12v, 1800wh (including 50% discharge rate and 80% battery efficiency)
- 220-230VAC
- 7.5 hours charging at night.
- 1800/7.5 = 240wh of charging.

-> 300w inverter (with sell back option)?
-> Power supply/battery charger?
-> Charge controller?

It almost always not cost effective to try and load shift/buy at night and sell during the day. A set of good quality lead acid batteries, last time I worked out the costs, was around $0.45 per kWH (cycling batteries wears them out). Take cost of batteries and divide by cycle life * kWH per cycle--See what you get.

I can buy power at $0.09 (to $0.27--I have "tiered pricing--the more I use, the higher rates I pay) per kWH and sell it at ~$0.27 to $0.50 per kWH with my utility. I would just about break even just on battery costs alone at the most optimum spread--which might not even be possible with my utility rate plan.

Add the 82% of the youtube video system plus 80% battery efficiency, your purchased kWH costs would increase by:

0.82 conversion eff * 0.80 battery eff = 0.656 = 65.6% efficiency
1/0.656 = 1.52x my $0.09 to $0.27 per kWH purchased price of power

So, even poorer rate of return because of losses.

Note that I'll be testing this as a prototype which means I'm almost certain I'll use uncertified Asian products as a concept of proof for my school. Help is very much appreciated!

If you build the system... Install it on non-flammable backing/floor. Use concrete backer board (we use in bathrooms/under tile as it is water resistant). And put a "shelf" under your components/wiring (in conduit/metal pipe?) so that an flaming debries does not fall on the floor and set carpet/wood flooring on fire.

Remember, for your installation to be successful, has to operate 24 hours by 7 days a week without anyone watching/controllin it. You will be generating significant heat (as well as charging a battery which generates hydrogen gas and is filled with 30% sulfiric acid--And is capable of 100's of amps in a dead short).

For a school demonstration project--Yes, it can work. To be actually "safe" and "legal" to install in 20 homes--Just getting safety approval can cost $20,000 to $50,000+ with a local safety agency--And you would not pass using the equipment you are talking about right now.

In many countries, you need to use "Listed" equipment and get building+utility permits+inspections to install such a product. In the US, you could not with this system. You could with a "real" hybrid inverter system--Except where hybrid inverters are not allowed:

Conext XW Sine Wave Inverters and Accessories
SMA America Sunny Island

Edit: If this project succeeds, there are plans to test it out on 20 homes each with 2-5kwh battery system depending on the price. When this do happen, build quality and safety will be priority #1.

What you are thinking about doing will work. And can be done safely. And is the "Holey Grail" for utility companies (to store "excess" cheap generated/Renewable inverter in a battery bank/behind a dam for use later (load leveling/peak shifting/etc.).

Just about any sort of energy storage system you can think of--Has been tried at small and large (utility/city) scale.

The problem so far--Has been to make it cost effective. Batteries/storage/conversion losses (and cycling costs) have been a major issue--And conversion losses have been another. For places that have the topography--Pumped Storage (hydroelectric dams with bi-directional pumping) has been the most practical and efficient. But these do not down scale for home sized systems very well.

For most people, investing in conservation is a better return on investment and holds it value better than solar RE power systems and such.

In any case--Good luck and be safe.

-Bill (hopefully I got your IP address/access restored) B.

Delly · August 2013

Re: Using grid inverters without solar/wind

First and foremost I want to thank you for the welcome and everyone that replied. And yes as you can see, I'm unbanned. Thanks

It seems that I need to explain the purpose of the project further more since everyone is recommending me not to so.
As I stated in the beginning I live in a cold place, more precisely in Scandinavia. The thing is that in a certain place there are times where the power company reaches their maximum deliver capacity. This happens mostly in winters (xmas), but other times too. There are 2 solution for this problem. Build a new grid which will cost many MANY millions and most of the residents here don't like the look of them, or somehow let the people "help" the power company by installing some sort of solar solution. But in winter days with -10 to -20 deg Celsius neither of solar/wind helps. Not sure of how good wind performs in icy weather. So the only way of help reducing the top peaks is by either using power efficiency items (which can be thrown out of the window because the people here are to spoiled and would rather use more money to have a comfort and well light house) or use the load shifting option.

Yes it might not be cost effective, but if this helps reducing the peaks so there is no need for a new grid installation it is definitely worth it. This is where my research comes in. I have electronic/electro background and know the basic stuff, but pretty knew to the solar concept.

As for controlling the charge and discharge I'll be using a control unit which will work over GSM, GPRS, or Wi-fi as an app, web gui or sms. This is the next stage after this one here. Who will be in charge of the charging/discharging is not irrelevant to my project but can be both the house owner and or the power company.

Here is an example:
At a certain day in winter people come back home from work and start using electricity to warm up the house, water, cooking, tv etc. 100 houses at exactly 7 pm use over 3kwh each. This is a peak with over 300kwh. Now if 50% of those houses have 100% charged battery capacity of 5kwh, and they permit only 2kwh of use before recharging again that will be 2kwh * 50 = 100kwh. This equals to 1/3 of the peak reduced. Also, if some families are on vacation then this will lead to even more battery capacity should the power company need to do so. (in this example the power company is the one controlling the charging/discharging). Of course each contributer will then be well awarded for helping the power company not blowing up their grid capacity. When there is no "emergency" need of extra power by the power company, each family can use the stored energy as they please.

Now I hope you get a better picture of the situation here. So back to my topic, I've been given orders to build a cheap setup (mostly Chinese products efficiency is not a concern). This is only for "advertising" reasons. After that I'll go over to the good quality setup. By good quality, I'm talking about outback/victron stuff with as high efficiency as possible.

So the question is now: What do I need to make a cheap load shifting setup for a 1500-1800wh of battery capacity? Sell back or "helping" your neighbor/power company option is a must :P
I've made another draft of how I think the final setup (cheap one) will be like. Please do point out if there are problems or "bad" connection or something else. I'm the type to understand more from pictures than text

Also, which parts will be different with the expensive/quality setup?

Edit: I forgot to tell that the controller unit MUST have the remote option. thus wifi,gsm etc...

BB. wrote: »

I am not quite sure what your question is... PWM is a common engineering "tool" and is not a "thing" in itself. In your DC power supply, you probably have a PWM stage for controlling power transfer/output voltage+current characteristics.

Using a Power Supply vs a Battery charger--Yes it can be done, but there are issues. You are generally better off using a "real battery charger" as not all Power Supplies are capable of charging batteries (lots of possible issues).

The power supply is merely there just to act as a PV array.You can see that in the draft below.

BB. wrote: »

Note that most "hybrid" capable AC inverters include their own Battery Chargers too--And these battery chargers are usually pretty high-tech/configurable. Plus a true Hybrid inverter can give you "UPS" type function (uninterruptable power supply) type function (backup AC power for the home if utility power fails). Some even have AC2 input and automatic generator controls.

Are you saying that this unit alone + batteries will this unit alone be enough for my purpose?

BB. wrote: »

For Solar power systems, in general for smaller systems (~400 watts or less), PWM solar charge controllers are "good enough" for many smaller installations. For larger systems (~800 watts or larger solar array), a MPPT charge controller is usually better for multiple reasons (less copper wire costs for array wiring, better logging/control in high end MPPT controllers, etc.).

I'm aware of that. Therefore I'm thinking that a PWM is better for the test version, but I've heard that a PWM can have watts up to 3 time the rated usage but only use the 1/3 of the watts. Is this correct? I can find the video on the youtube later when I have time.

Attachment not found.

Once again, Thanks.
Delly

niel · August 2013

Re: Using grid inverters without solar/wind

sorry for only catching your last post, but by the description of your needs i think you are overly complicating things. if all have a backups with 5kwhs worth of batteries and a psw off grid inverter of the proper rating you could just come home and flip a circuit off the grid and proceed to use about 2kwhs worth of power from the batteries. this won't take long to do if the load is at 3kw and that would need to have a larger battery bank capacity to handle the surge and voltage dropout batteries experience when heavily loaded. when the 2kwh is reached flip the grid back onto the circuit, but do not engage either a built in charger or external charger until the next morning. if all homes did that it would meet the goals you've set. no pvs or controller required, but can be added for an extra cushion should it be desired.

if on the other hand i did not read enough then you can ignore me on this.

Cariboocoot · August 2013

Re: Using grid inverters without solar/wind

Now you are talking about time shifting ("load shifting" is changing the time when loads are operated to meet available power) for very large loads: electric heat, stove, et cetera. There is no way to do that "small and cheap" because the loads themselves demand very large amounts of power. A 300 Watt inverter, for example, would have no use at all in such an application. The other household loads will probably also be quite substantial when added together.

You mention a 5kW hour battery capacity. On a 48 Volt system that would be at least 232 Amp hours, which is not unreasonable.

Selling back from the battery capacity is not so easy, as battery-based GT systems rely on battery Voltage being above a certain point (fully charged) before sell-to-grid is enacted. Pulling power from the batteries below that point is only done to power loads in the event of an outage.

So you have a case where removing the load strain of a particular household from the grid total is fairly easy, but asking it to contribute to the grid production is more difficult.

Some other observations: solar works fine at -20 or even -40, it only needs sunlight. However it doesn't work fine at 7:00 PM in Winter in Scandinavia.

A solar charge controller of either type would not be involved in such a system because there are no solar panels. They are not used for regulating battery charging from AC sources; any battery charger will have such regulation built-in, and an inverter-charger will function best for this.

vtmaps · August 2013

Re: Using grid inverters without solar/wind

Delly wrote: »

There are 2 solution for this problem. Build a new grid which will cost many MANY millions and most of the residents here don't like the look of them, or somehow let the people "help" the power company by installing some sort of solar solution.

If battery storage would help the power company, they should install their own batteries... they can do it cheaper and better (economy of scale) than you and your neighbors can.

You can help the power company by disconnecting from the grid and using your batteries to supply your own loads (as Niel suggested). You don't need to sell power from your batteries.

--vtMaps

NorthGuy · August 2013

Re: Using grid inverters without solar/wind

Delly wrote: »

What do I need to make a cheap load shifting setup for a 1500-1800wh of battery capacity? Sell back or "helping" your neighbor/power company option is a must :P

There are ready made hybrid inverters, such as Xantrex or Outback, which are relatively easy to set up for your application. I don't really know if it is something of this kind in 1-2kWh range. All I know starts from 3-4kWh. Plus you'll need expensive batteries which will not last forever. You should expect at least 30% energy loss through the battery cycle.

Another possibility is to use fossil fuel generator(s) to complemet grid at peak hours.

Cariboocoot · August 2013

Re: Using grid inverters without solar/wind

Also, when it comes to selling back to the grid the utility connection has to be 'designed' to be back-fed. Otherwise there is no point in trying to feed the grid from the house. It may not even be legal to do so.

Taking the load off the grid and on to batteries at peak electrical usage times is something that can be easily accomplished by a homeowner without the need for any interaction with the utility company. This is probably the best bet for alleviating brown-out scenarios, although as mentioned before it will not be inexpensive.

BB. · August 2013

Re: Using grid inverters without solar/wind

There are also co-generation solutions... Depending on the price of various fuels in your country, this is a home sized unit designed for colder regions...

Hmm, after looking around the "Freewatt" system (smaller Honda grid tied generator+using waste heat for hot water/heating). Looks like it is no more. I cannot really find a working website after ~2012.

-Bill

SolarPowered · August 2013

Re: Using grid inverters without solar/wind

All I can say to the thread starter..
Get off the grid.
Find methods in creating energy. Take a chemistry class to make your own fuel like hydrogen.
WARNING: Do not attempt unless you have the ability to be trained in producing and containing hydrogen.
I have a method of producing hydrogen via 2 watts of solar, yet trying to explain it to novices could get them killed. As easy as the production is it can be dangerous.
However hydrogen generators is the direction that the back yard energy producers are going. There are loads of youtube vids on sterling engines and how to make hydrogen, then its up to you to think outside the box, with a little education behind it.
http://www.youtube.com/watch?v=X3qb1Wc1j5g
http://www.youtube.com/watch?v=Zxhve2OmrYc
http://www.youtube.com/watch?v=xyDdEuQafn4
http://www.youtube.com/watch?v=f-HkVlq1kcQ
Hydrogen is safe (if produced and contained correctly) and after initial investment its free, You just have to be highly trained to know how to work it as it can be volatile in some conditions.
Hydrogen can be used for numerous power generation from sterling engines, to combustion engines.
Its the way the world is moving towards because hydrogen has more energy potential than bio diesel, and hydrogen emits little to no hazardous emission. The auto industry hates it because its an abundant resource....WATER.....
Expand your mind, relative answers to somewhat "almost free" power is out there.
Taking power from the grid which you pay for and storing it in a high resistance battery is not the answer.

BB. · August 2013

Re: Using grid inverters without solar/wind

I will argue that hydrogen is not a "fuel source" in itself--It usually has to be created from some other form of energy. At this point, at least in the US, the cheapest source if hydrogen is from breaking down natural gas...

I would never suggest that anyone without lots of knowledge and experience tackle hydrogen storage and piping... There are just too many ways for things to go wrong. Even "professionals" still have problems with hydrogen (it appears that India just had a diesel electric Russian mfg. submarine catch fire/blow up at dock taking out the shore crew--first guess is a hydrogen explosion).

In any case, the original poster is from somewhere around Norway--So they just do not have a lot of sun in the winter--But, summer use of solar (vacation cabins and such), is very popular (as I understand).

And he is looking for lots of power for winter heating... One option is time shifting power usage--Charging the battery off peak and running some sort of heating system on-peak is one option.

Using some sort of heat storage system (water, wax, molten salts) would be another option (heat the storage medium off peak, draw down on peak). Just using a heat pump and some sort of thermal mass would be another (air source, ground source, well water, etc.)... Generally, using lead acid batteries to run resistance heating is expensive.

Using a modern air source heat pump in Norway may be possible...

http://energy.gov/energysaver/articles/air-source-heat-pumps

Advanced Technologies: Cold Climate Heat Pump

One company has developed the cold climate heat pump, which features a two-speed, two-cylinder compressor for efficient operation, a back-up booster compressor that allows the system to operate efficiently down to 15°F [-9C], and a plate heat exchanger called an "economizer" that further extends the performance of the heat pump to well below 0°F [-18C]. The system has been tested favorably by several utilities and may soon be available to consumers.

Advanced Technologies: All-Climate Heat Pump

Another promising technology is an All Climate Heat Pump, which the manufacturer says can operate in the coldest days of winter without supplemental heat, maintaining comfortable indoor temperatures even when the temperature outdoors falls below zero. The heat pump could reduce heating and cooling costs 25% to 60%.

While the design of most heat pumps puts the focus on cooling, the All Climate Heat Pump was designed with heating as the primary focus. Initial costs for the All Climate Heat Pump are high, but if it continues to work as well as predicted, the energy savings over the life of the system would more than compensate for the up-front cost.

-Bill

Delly · August 2013

New Update

Yesterday I had a meeting with project manager and project supervisor. After explaining to them the bad side of having a bad quality test setup and its inefficiency they made a small change to the project criteria.

Now I can use up to 10x more money on this research meaning that I can skip the low quality stuff and go straight to the good quality setup.
However, there are conditions to be met, and I need to fulfill them within 2 weeks.
1) Still a load shifting (or time shifting, not sure of the difference) setup but!
2) Must be designed for PV arrays.
3) Future proof meaning that it should be possible to sell back to the grid in the future (or now for testing purposes)
4) Still use a remote control to regulate the charging/discharging. (looking at wifi/zigbee/app. not a big concern right now)

The purpose of load shifting will be primarily winter usage, and the solar will be in summer. The solar can be used in winter if there is sun too. FYI, sun in winter is no more than 2-5 hrs and with 20-40% of brightness (clouds not taken into account!) compared to sun in summer.

I usually am not the kind of guy who only wants one answer and refuses others in forums or real life, I really do appreciate other ideas, suggestions and recommendations not related to the topic. But for this matter I would appreciate it if I could get answers related to the topic. As I stated earlier I'm doing a research, and a part of the research is proving something either works or not with well documented paper which is what I'm trying to do here.

After approx 2 months of research I somewhat know what is needed for a regular on/off grid battery GT system, but what I really have no idea about is how to combine both load shifting and regular on grid system. My supervisor told me yesterday that not all GTI are designed to be supplied by batteries and might burn up. What sort of GTI should I be looking into to combine both load shifting and regular on grid system? Note the word combine. Right now I'm really confused. If the charge controllers do not support dc input from power supply/battery charger and not all GTI support power from batteries, then what is the solution? I feel like my 2 months of research was a total waste of time...

What about microinverters? Would it be pointless to have microinverters for the PV + regular GTI for the load shifting? After a quick research it seems enphase microinverters do not support battery system, but what if I were to use a normal microinverter system and then use a battery charger to charge the batteries and put it back to the house through a regular GTI? It does sound silly, but not sure if it would cost even more than my research system...

Lastly, I was hoping that someone would comment whether my last sketch/draft is correctly configured and or if there are unnecessary/lacking parts, Because I'll soon have to start on describing the functionality and describe the pros and cons of the system, then make a big order list for my project manager to buy the setup. This is the first time I get such a big responsibility and the thought of making a mistake somewhere and that no one will be checking the order list in details besides me myself is making me somewhat scared

Your help is much appreciated, trust me!

As Always, Thanks
Delly

NorthGuy · August 2013

Re: New Update

Delly wrote: »

Now I can use up to 10x more money on this research meaning that I can skip the low quality stuff and go straight to the good quality setup.
However, there are conditions to be met, and I need to fulfill them within 2 weeks.
1) Still a load shifting (or time shifting, not sure of the difference) setup but!
2) Must be designed for PV arrays.
3) Future proof meaning that it should be possible to sell back to the grid in the future (or now for testing purposes)
4) Still use a remote control to regulate the charging/discharging. (looking at wifi/zigbee/app. not a big concern right now)

With that much money, you can go with a hybrid inverter, such as this, which meets all of your criteria.

Delly · August 2013

Re: New Update

NorthGuy wrote: »

With that much money, you can go with a hybrid inverter, such as this, which meets all of your criteria.

So you're saying this is capable of load shifting alone, solar alone or both if wished so? 6kwh continuous is a bit much. Remember that I need batteries too. 1/2 or even 1/4 that size would be more than enough for this research's purpose. I see that Conext XW4548 has an affordable price. I'll think about it or the 24V one, IF, and only if it really does all what I'm looking for.

There is one thing that come to my mind, with many small system it is easier to control and configure things the way you want. But with this all in one big daddy system, I'm wondering how I can remote control it. With the small setup I was thinking of connecting a zigbee plug into the wall outlet and connecting the battery charger to the zigbee plug. The zigbee will be connected to a router which will give me the access to turning it on or of. I'm not sure if this is the proper wait or if it work at all, but at least that's what I had in mind. For this one, I'm not so sure yet. Does these types of inverter usually have some sort of wifi control?

Do this inverter do the same thing as the one above? In the video it seems I need to add CC and or other parts I which I'm guess I don't need to do with the XW?

As Always, Thanks
Delly

Cariboocoot · August 2013

Re: New Update

4) Still use a remote control to regulate the charging/discharging.

I do not see any point in this. It is possible the requirement is not being expressed clearly. This function as stated should be automated within the system; there is no purpose in having external control over it. Is it possible this refers to remote monitoring of system status?

To be PV capable it only needs to have batteries, which it will: PV charges batteries through charge controller, the rest of the system continues to function as-was. This can include sell-back to grid.

To be grid-feed capable the inverter needs to be of the hybrid variety such as the Xantrex XW, Outback Radian (or G series). With "SELL" turned off it will only take from the grid as needed.

Simplest TOU shifter:
Use a timer such as those meant to control electric hot water heaters to control the connection between the grid and the inverter's AC IN. When grid rates (or demands) are low timer is on, feeding all loads including those connected to AC OUT and charges batteries. When grid rates (or demands) go high timer turns off, disconnecting inverter subsystem from the utility. Loads on AC OUT are powered by inverter from batteries. Switch-over is seamless. This does not allow for sell-back to grid.

Adaptation to utilize solar and sell-back: separate GTI system fed to grid directly. When PV's are active they will provide power to any loads on the AC side, including feeding inverter-charger to keep batteries up. Surplus (if any) sells back to grid. It is also possible to devise a system where the PV & GTI is AC coupled to the battery-based inverter to keep it charged in the event of a grid outage (SMA's Sunny Island coupled with PV driven Sunny Boy).

BB. · August 2013

Re: New Update

Hmm...

First, like NorthGuy suggested, the Schneider XW would be one system. There is also SMA out of Germany that has a very nice "Sunny Island" system that apparently, has an undocumented capability to sell battery/DC power back out and sell to the grid. And there is at least one or two more other vendors that have that capability too (I think, out of Germany, but I don't remember the names--We don't see their products in the US).

While European products are usually pretty expensive for us--They are probably more cost effective for you.

I understand your desire to stick with Inverter/Battery solutions-That is fine. We here try to approach solutions from all sides--Conservation/Efficiency/alternatives can really save a lot of money--Sometimes upwards of 50% of energy usage--Which cuts the size of a a very expensive Off Grid/Hybrid system costs by 50% too.

Any way... You are being a bit "unclear" when talking about the solar/grid tied/hybrid power systems and their capabilities... And I want to make sure that you understand what is possible with these units--If not always practicable.

First--A "simple" TSW (True Sine Wave) AC inverter... The higher end units can have networking, programmable parameters, remote On/Off inputs (handy to turn off an inverter without a huge DC relay on the input power), Remote Generator Control (can be used to turn on/off grid charging like a generator), several AC inputs (grid/generator), ability to support generator (or grid) output (i.e., if you have a 15 amp AC generator output and have a 20 amp AC load, the inverter can "support" the generator by supplying the extra 5 amps, etc.). Also, they can come with a pretty sophisticated internal battery chargers ("share" AC input maximum current from source between supplying AC loads and recharging battery bank at the same time--i.e., more AC load, cut back on AC charger; different charging algorithms; power factor correction--More "efficient use" of AC current; etc.).

Next--There are non-traditional ways of flowing power through an off grid AC inverter... For example, you can actually push AC power "backwards" through some sine wave AC inverters and recharge the battery bank. You can mix this feature with a pure GT inverter's AC output and create a "micro grid". Basically--The off grid inverter makes AC power--as you expect. And then you take a standard GT inverter+solar panel or array and connect it to the output of the off grid inverter. Now, the OG inverter will set the "voltage and frequency" of the grid and supply energy to the loads. And the GT inverter will "back feed" the AC grid and support the AC loads, and even feed energy backwards through the OG inverter and recharge the battery bank (there needs to be charging control to make sure the batteries do not over charge. The SMA Sunny Island system does this all very nicely. Some other AC OG/Hybrid AC inverters are starting to incorporate charging control too--basically knock the GT inverter off line by varying the AC line frequency by +/- 1% which turns of the GT inverter for ~5 minutes--The SMA system is even more sophisticated).

A Hybrid Inverter can both act like a standard Off Grid inverter and supply AC power to local loads when the grid is down (or in an off grid situation where there is no utility power available). And, like a Grid Tied Inverter, it can feed excess power back to the grid when the grid is up and connected--if the battery bus has "excess" DC power available (sun is up, micro hydro system is generating DC power, wind is blowing and charging battery bank, etc.).

And, another way to control power; many GT AC inverters (which have no battery connections) and MPPT solar charge controllers (traditionally used to control battery charging from solar panels) can actually take DC power from other sources besides solar arrays... You can also connect wind or water turbines. Or even in some cases, a DC Battery bank and the controller will use that power (GT Inverter will output grid compatible AC power, or a MPPT charge controller can take 24/48 volts from one battery and use it to charge a 12 volt battery for other 12 volt only loads).

Plus, many products (MPPT type charge controllers, a few battery monitors, etc.) have some sort of aux output controls... Besides automatic control of generator--Some outputs can be used to turn on "opertunity loads" -- Such as water heating when the batteries are fully charged. Or used to cycle a battery bank / control a genset (or AC battery charger) to daily cycle a battery bank (for example) from 50% to 80% state of charge 6 days a week (this is more efficient and, in some ways, better for a lead acid battery) and only recharge to 100% one day a week.

And newer equipment has Ethernet networking built in (logging of data, sometimes reconfiguring of parameters), or Mod Bus/other RS 422/RS 232 com channels--Usually used to monitor/log system activity.

For example:

My supervisor told me yesterday that not all GTI are designed to be supplied by batteries and might burn up. What sort of GTI should I be looking into to combine both load shifting and regular on grid system? Note the word combine. Right now I'm really confused. If the charge controllers do not support dc input from power supply/battery charger and not all GTI support power from batteries, then what is the solution? I feel like my 2 months of research was a total waste of time...

I am terrible with using engineering terms consistently (and English is my only language--just barely

).

Typically, around here, GTI or Grid Tied Interactive AC inverters are simply a "black box" where you connect one side to a power source (typically solar array, sometimes wind/water turbines) and it figures out the maximum available energy from the DC power source and then "inverters" that energy to output to the grid (assuming that the grid acts for all the world like a giant AC battery bank--which can supply a huge amount of power or receive a huge amount of power without varying voltage or frequency). This is very similar to the way your car's charging system works. The battery (AC grid) sits in the middle and is really controlling the DC voltage to ~12-14.2 volts. It will supply current (when loads are greater than alternator's output) or receive current (when alternator output is greater than the loads).

So, a traditional GTI or GT Inverter does not connect to a battery at all. There are things to watch out for--You could put a battery on the input to a GT Inverter and the inverter will pretty much take all the energy the battery can supply and output the inverter's maximum rated output (say 3-5kW) to the AC grid connection until the battery is dead or the GT Inverter is turned off some how. And while that should not hurt anything, there is the difference between a "standard" generator (or inverter) output rating and "Prime Mover" rating... Basically, when you run a generator or inverter at 100% of rated output for hours/days/weeks on end--They get hot and can eventually "cook" themselves. So, there is "Prime Mover" rating which is something like 80% of its maximum rating and intended to represent the capabilities of the power source when it is the only source of power (i.e., the "prime" power source vs using the grid and the local power source is just emergency backup). So--It is possible to damage many "commercial" and residential power sources if you try to run them at 100% rating.

For your needs--I like to back it up for a moment. What exactly do you have (i.e., a 220 VAC 50 Hz grid connection. A 3 kWatt load/electric heater/heat pump system) and your needs (need to run 3 kW heater for 4 hours 7 days a week during winter). And your alternative/possible power sources (ZZZZ Watt solar array mounted in Oslo Norway, a YYYY Watt Genset for emergency backup power or even for use as a co-generation heat source)--And such.

In general, the simplest way to design such a system is to define the needs of the Battery Bank (power in, power out, hours of use per day, etc.). and make that the "heart" of your design.

For a first approximation, each load/power source can be thought as completely independent from each other (i.e., the Hybrid Inverter will take power from the battery bank or return power to the battery bank--It does not "matter" if the battery bank is also connected to a solar array or a hydro powered turbine+rectifier, etc.). Each "circuit" needs to be designed to support the intended loads. And the battery bank needs to be sized to support the "worst case" intended loads (and even power sources too).

There is interaction too... For example a Hybrid AC inverter can feed power back to the grid--It does this by acting like a diversion or shunt controller... For example it will try to hold a fully charged battery to 52 volts (float--for a 48 volt battery bank). If the battery bank is being "charged" by a solar array or other power source, the Hybrid Inverter will start pulling power from the DC battery bus as the voltage rises above 52 VDC. When the sun starts setting, the Hybrid Inverter will reduce its DC power draw to near zero and stop exporting AC power to the grid/home power system.

Anyway... Inverters, chargers, battery banks, etc...--They are designed for specific size (wattage) systems. The devices that work well for a small system (300 watts) are not usually the same ones that work well for a 3-6 kWatt system....

So, size matters here in the basic design (points you to a "class" of equipment that can meet your needs). And other requirements (such as backup generator) will affect choices too (and how that generator is used--24x7 for most of winter, or just a few 10's to 100's of hours per year as emergency backup).

Is this making sense to you? This is a complex subject--And for the first time through for anyone--I suggest designing to a specific set of requirements vs trying to understand all possible configurations/options/possibilities. This is a very complex subject and all of the "caveats" can easily confuse (this works for a small system, if you have a 24x7 generator then an Off Grid inverter that has "generator support" can let you choose a smaller/more efficient generator and still support surge loads like a well pump, running an induction stove at the same time--etc.).

-Bill

SolarPowered · August 2013

Re: New Update

To me it sounds simple enough.
He needs an island inverter with GT inverter combo.
SMA would be the only direction to move forward in.

As far as typical heating needs it would require a very large battery bank. That in which is storing the potential energy during mid spring, summer, and mid fall conditions. In other words expensive, not cheap.

So instead of a massive battery bank the solution for BTU efficient conversion out put would be bio-diesel, or natural gas there is no real way around the problem accept for substitutions of an effective cheaper energy source.

At least with bio diesel it's extremely safe to store in a 500 gallon totes in a garage , can run a pump for a generator, or heating needs.

stephendv · August 2013

Re: New Update

There are some inverter/chargers that will sell to the grid from batteries, but the tricky part will be programming them to sell or to charge on the fly based on your own criteria. So with all the options below I think you'll need to use your own mini-pc or microcontroller to make the decision about when to sell and when to charge.

Some options:

1. Outback GTFX inverter/charger + charge controller, http://outbackpower.com/index.php/outback-products/inverters-chargers/item/sealed-gtfx2012e-50hz?category_id=444 The system uses a "Mate" device for programming, you'll have to investigate how easy it is to change the mate programming from an external PC.

2. SMA sunny island 2224 + ( Sunny boy or charge controller), http://www.sma.de/en/products/off-grid-inverters/sunny-island-2224.html#Technical-Data-8976 This can be programmed through SMA's published spec, and SMA also have an open source library called YASDI that you can use in your own programs to talk to the sunny island and sunny boy.
Although the SI can sell to the grid, I don't know if it'll do so when purely on battery power. You might be able to hack a solution together with YASDI if you can program just the right settings. E.g. if you want to sell to the grid from the batts (and not the PV), then set the battery charging voltage to say 23V on a 24V battery, I THINK the SI will then see this as surplus power on the batteries and start selling to grid in an effort to bring the voltage down to 23V. When you want to charge, just change the charge settings back to their normal values.

Delly · August 2013

Re: Using grid inverters without solar/wind

I'm Leaning more towards the conext inverters because they are in a sense an "all in one" solution". But I'm not quite sure which one of the SW/XW I should go for. Now obviously, the reason I want to go for the SW is due to that XW is too large for my purpose, but it's pretty new, and I haven't heard or seen anyone using it on the internet yet.

Anyone knows if SW is capable of doing the same thing as XW since it's the "little brother" except in a smaller scale?

Also, why do some people recommend off grid inverter to me, when I'm connected to the grid 24/7? I thought that only on grid inverters would fit in...

Delly

mike95490 · August 2013

Re: Using grid inverters without solar/wind

Which one ? What sort of power do you need - 120VAC, or 240VAC ? Do you need a really big charger built in ? I'd never suggest anything less than a XW nn24, from my life with the big honker XW-6048.

BB. · August 2013

Re: Using grid inverters without solar/wind

The XW inverter--It can do everything the SW can, plus it can feed power into the grid and turn the utility meter backwards (Grid Tied, or utility interactive inverter function).

If you do not want to feed power back to the utility grid (slightly more expensive hybrid inverter, need to get an agreement with the utility and a rate plan to properly keep track of feeding back to the utility), then you can use the SW inverter and just cut the AC mains to the inverter can power everything down stream from the inverter directly from the battery bank.

These are very complex units with amazing functions built in with (for the most part) seamless transition from AC battery charging, to feeding excess power backwards to the grid (if battery bank is being "charged" by solar array), to UPS function (AC power, switch over to battery+inverter), to starting a genset when the battery gets low--And "supporting the generator" (with battery power through inverter) if the AC loads exceed the ability of the generator to support the load.

What you are asking for--Basically in winter when a home needs "lots" of electricity during peak power times for electric heat (to off load utility lines/generators or "peak shaving" with a distributed power system--local batteries+inverters in home) is not a function that is (usually) built into a standard inverter. If there is enough market for it, then somebody may add that function and sell it.

However--This is why I come back to try and understand what your needs are... If it is pure heat, as Chris Olson mentioned in another thread, his electric hot water heaters are a better short term storage system than his battery bank--If the stored energy is heat.

If I got the right equation:

0.001163 of one kilowatt-hour to heat your liter of water from 0°C to 1°C

So, say you want to store 10 kWH of energy as heat--And your water temperature is from 50-100C...

10 kWH * 1/0.001162 kWH per liter per degree C * 1/(100-50 C change) = 172 liters (45.5 gallons) of water

So--A couple electric heaters to heat a well insulated water tank during off peak. A pump + radiator to circulate water to bring the home up to a comfortable temperature.

If you want to even store more energy in fixed space more efficiently--Replace electric heather with reversible heat pumps and cool the water to freezing and include the phase change energy storage too...

-Bill

Delly · August 2013

Re: Using grid inverters without solar/wind

BB. wrote: »

The XW inverter--It can do everything the SW can, plus it can feed power into the grid and turn the utility meter backwards (Grid Tied, or utility interactive inverter function).

If you do not want to feed power back to the utility grid (slightly more expensive hybrid inverter, need to get an agreement with the utility and a rate plan to properly keep track of feeding back to the utility), then you can use the SW inverter and just cut the AC mains to the inverter can power everything down stream from the inverter directly from the battery bank.

Thanks for pointing that out for me. I kind of skipped over the cannot sell option. I'm not really concerned about the generator option, but I guess it's a good thing to have.

BB. wrote: »

However--This is why I come back to try and understand what your needs are... If it is pure heat, as Chris Olson mentioned in another thread, his electric hot water heaters are a better short term storage system than his battery bank--If the stored energy is heat.

I thought I did make myself clear somewhere out there. It is not clean heat. The major consumers are: heating, cooking, charging el.car (this one is getting more common). Then there are the every day things such as tv, pc, hair dryer, etc... So the point is not to eliminate 1 thing completely, ie charging car, but reducing the total load by 10-20% AT DEMAND (when needed/critical)

Anyone knows where I can look up for prices of conext sw and xw? There is nothing in Norway. Many of the sellers requires that your registered before they will give you a price on their products. The worst part? Mostly of them are in brochures!! Couldn't find anything in amazon either, except for one dealer which has a ridicules price of $3,200 for the cheapest one and they don't even ship outside US. =(

I'm making my order list today for the university which needs to be finished before tomorrow morning! Here, I must describe in details what the required functions for the project are; what the product(s) will help with, how and what can/cant they do; why I've chosen these products, etc... Feeling the rush now, EEEK! :P

EDIT: I'm doing some calculation for battery/PV size but I am getting a little bit confused. Please correct me if I'm wrong.
Battery size:
3750Wh/24V (including 80% batt eff. + 50% discharge). Will be using 750Wh for 2 hrs = 1500W.

Array size for charging up with 5 hrs good sunlight:
Since battery state = 50% discharged I need a minimum of: 1900Wh / (5hrs * 0.8batt eff * 0.77 CC+panel eff) = 617Wh
Nominal size: 3750Wh / (5hrs * 0.8batt eff * 0.77 CC+panel eff) = 1220Wh. Isn't this way too much/big for 750wh of use for 2 hrs!?
When charging through panels, the current wont go through the inverter, hence it's not taken into account when charging. Will only be Panels -> CC -> Batt. when charging. Pretty standard, right?

Also, when I'm charging through grid, aka load shifting, I'll be charging the batteries for 7.5 hrs. What do I need to account for here? Inv + batt eff + 7.5hrs + anything else?

Last bonus question, do I need to take into account the battery efficiency when charging up, once again? Note the word once again! I'm thinking that I've already done that in the first step when I calculated the battery size (3750Wh).

Thanks in advance,
Delly

BB. · August 2013

Re: Using grid inverters without solar/wind

Delly wrote: »

Thanks for pointing that out for me. I kind of skipped over the cannot sell option. I'm not really concerned about the generator option, but I guess it's a good thing to have.

The XW is pretty competitive in terms of pricing for pure off grid use too... Many people use them only off grid and will never use the GT function--And are very happy.

I thought I did make myself clear ... It is not clean heat. The major consumers are: heating, cooking, charging el.car ... but reducing the total load by 10-20% AT DEMAND (when needed/critical)

You did--I just wanted to make it clear that there are other options (for you, and for other people who will read this discussion in the future) to not fixate on solutions--but remain flexible--Especially on heating. In general, we try to discourage resistance heating with off grid battery systems... Resistive heating is just not very cost effective when you take the cost of battery cycling into account:

Trojan T105 6 Volt, 225 AH Deep Cycle Battery @ $151 each (plus shipping+taxes)

Using this generic battery life vs depth of discharge:

http://www.solar-electric.com/deep-cycle-battery-faq.html

And assume you buy a new $1,500 AC inverter every 10 years...

50% depth of cycle gives a battery life of ~1,000 cycles. Say you do 1,000 cycles every 5 years or 1,000/5=200 cycles per year (and the battery ages out in 5 years). 4 battery bank for 24 volts. And this would be 2,000 cycles over ten years:

($1,500 inverter + 2 battery sets * 4 batteries * $151 per battery) / (2,000 cycles * 6 volts * 225 AH * 0.50 discharge) = $0.0005 per WH = $0.50 per kWH

So--Just the "privilage" of running 10 years of a time shifting system (with 10 year inverter life and 5 year battery life, using "cheap/cost effective" batteries) is still in the range of $0.50 per kWH peak summer rate... In California that is our most expensive rate...

And, if I charged from the grid at night, with tiered rate pricing (use more, pay more per kWH), my >900 kWH per month cost of electricity for summer afternoons is ~$0.54 per kWH and off peak is ~$0.30 per kWH... The total cost of my "shifted power" would be:

$0.50 per kWH hardware + ($0.30 per kWh)*1/0.85 charger efficiency*1/0.80 battery efficiency*1/0.85 inverter eff = $1.02 per kWH for buying off grid power and shifting it to peak power usage

That is why, for me, time shifting my loads using a battery bank usually does not make economic sense (at least at this time).

Anyone knows where I can look up for prices of conext sw and xw? There is nothing in Norway. Many of the sellers requires that your registered before they will give you a price on their products. The worst part? Mostly of them are in brochures!! Couldn't find anything in amazon either, except for one dealer which has a ridicules price of $3,200 for the cheapest one and they don't even ship outside US. =(

Our host does list their prices online (Northern Arizona Wind & Sun), and they do ship outside the US.

http://solar-electric.com/

Whether they would ship to Norway, or can do it "cost effectively" -- I don't know (and you probably need 50 Hz / 230 VAC versions of some of the equipment--which may cost more/not be on their website)... You will need to contact them directly. Us moderators do not work for NAWS and have no idea about their business model--other than what we see here in the form and on their website.

I'm making my order list today for the university which needs to be finished before tomorrow morning! Here, I must describe in details what the required functions for the project are; what the product(s) will help with, how and what can/cant they do; why I've chosen these products, etc... Feeling the rush now, EEEK! :P

WE have a few European folks here that may be able to make some suggestions on suppliers that are closer to you and will not have additional duties/customs charges.

EDIT: I'm doing some calculation for battery/PV size but I am getting a little bit confused. Please correct me if I'm wrong.
Battery size:
3750Wh/24V (including 80% batt eff. + 50% discharge). Will be using 750Wh (note this is 750 watt load, not WH) for 2 hrs = 1500W.

Let me try my math/formula:

3750 WH / 24 volts = 156 AH battery bank?
156 AH * 24 volt battery bank * 0.85 AC inverter eff * 0.50 maximum discharge = 1,591 WH available capacity at 20 hour discharge rate

You are looking to discharge the battery at 750 Watts for 2 hours (1,500 WH discharge)... That is aproximatly a 4 hour discharge rate. For a flooded cell battery, your C20 capacity is 156 AH, but your C₅ discharge rate may be closer to 128 AH capacity--You might want a larger bank.

For example, the C₅ discharge rate capacity for a Trojan T105 225 AH battery is 185 AH... If you are using flooded cell batteries, I would suggest "golf cart" batteries at 6 volts and 225 AH would be better for your load testing... If your batteries are 156 AH at C₂₀ rate, they may be a bit on the small size (if AGM, many can sustain much higher discharge rates--But AGMs are 2x as expensive and don't usually last more than a few years in heavy current draw applications--such as computer power UPS systems).

Array size for charging up with 5 hrs good sunlight:
Since battery state = 50% discharged I need a minimum of: 1900Wh / (5hrs * 0.8batt eff * 0.77 CC+panel eff) = 617Wh
Nominal size: 3750Wh / (5hrs * 0.8batt eff * 0.77 CC+panel eff) = 1220Wh. Isn't this way too much/big for 750wh of use for 2 hrs!?

Two calcuations... First, based on size of battery bank (Big AH battery banks need higher charging current). 5% to 13% rate of charge for a C₂₀ battery bank rating of 24 volts and 225 AH (also known as AKA as 4x6 volt golf cart batteries in series). And since you are heavily cycling (50% is pretty deep cycling), I would suggest 10-13% rate of charge minimum:

225 AH * 10% = 22.5 nominal battery charger recomended (any AC/DC charger output current)
225 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 847 Watt nominal array

If you are assuming 5 hours a day of sun (this is probably true during summer)... But panel angle, one or two axis tracking, snow on panel/snow on ground, etc. all affect performance. If I was to pick an average for Olso Norway with a fixed array:

http://solarelectricityhandbook.com/solar-irradiance.html

Measured in kWh/m²/day onto a solar panel set at a 30° angle (degrees from vertical for this website):
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun

0.94
2.04
3.21
4.05
4.98
4.77

Jul
Aug
Sep
Oct
Nov
Dec

4.92
4.31
3.52
2.13
1.27
0.71

I would be hard pressed to pick 5 hours for a fixed array in Norway... If you did a full 2axis tracking, I am sure you can do better in summer. I would pick closer to 3 hours for 7 months of "OK" solar production:

750 watt load * 2 hours per day * 1/0.77 panel+controller derate * 1/0.80 batt eff * 1/0.85 inverter eff = 955 Watt panel based on loads

When charging through panels, the current wont go through the inverter, hence it's not taken into account when charging. Will only be Panels -> CC -> Batt. when charging. Pretty standard, right?

But to draw the load from the Battery Bank, in your case, the DC power goes through the AC inverter to be converted to 230 VAC 50 Hz--So, if your 750 Watt load is AC--Then you need to "add it" to the total system efficiency (losses).

Also, when I'm charging through grid, aka load shifting, I'll be charging the batteries for 7.5 hrs. What do I need to account for here? Inv + batt eff + 7.5hrs + anything else?

As good as rule of thumb as any to start... Your charging time will be the AH replaced + 2-4+ hours (2 hours for shallow discharge, 4 hour for deep discharge). For example:

750 watt * 2 hours * 1/0.85 inverter losses * 1/24 volt battery bank = 73.5 AH @ 24 volt consumed
73.5 AH / 22.5 amp battery charger (assuming 10% of 225 AH battery bank) = 3.3 hours of charging (assuming perfect battery)
3.3 hours + 2 hours (10%-20% discharge) = ~5.5 hours charging (shallow discharge)
3.3 hours + 4 hours (20-50% discharge) = ~7.3 hours charging (deeper discharge)

If you have a commercial tracking battery charger with their charging algorithms, your battery bank will probably charge faster (solar power systems can only charge with available power from sun--and have mixed loads+charging cycles--Not nearly as "simple" as grid power+Industrial Charger+Run on battery, park forklift and charge).

Last bonus question, do I need to take into account the battery efficiency when charging up, once again? Note the word once again! I'm thinking that I've already done that in the first step when I calculated the battery size (3750Wh).

I did not quite follow your math--So I am not sure... But as you see, I (usually) am very careful not to double up on deratings.

We do use different equation sets depending on questions asked/answers provided... The overall system efficiency calculation of 0.52 derating and hours of sun just runs all of the individual calculations together with "worst case" system operation (100% charge during day, all loads are at night+AC power/losses, from battery bank):

2 hours * 750 Watts of AC power * 1/0.52 end to end derating * 1/3.0 hours of sun fixed array = 962 Watt "break even" array

(round off error between 955 Watt vs 961 Watt results)...

If you are within 10% of predicted values for solar/off grid power--You are "right on the money"... there are enough "fuzzy numbers" (battery capacity, weather, temperature, human usage of power, measurement errors, variation in losses based on current flow, AGM vs Flooded cell, if a person operates their bank more in the 50%-80% state of charge vs 85%-100% SOC range, etc.)... That trying to be more accurate is usually not worth the trouble. (I do plug in 80% for flooded cell vs 90% for AGM batteries--depending on poster's desires).

-Bill

NorthGuy · August 2013

Re: New Update

Delly wrote: »

So you're saying this is capable of load shifting alone, solar alone or both if wished so? 6kwh continuous is a bit much. Remember that I need batteries too. 1/2 or even 1/4 that size would be more than enough for this research's purpose. I see that Conext XW4548 has an affordable price. I'll think about it or the 24V one, IF, and only if it really does all what I'm looking for.

Yes, you can do load shifting alone. It doesn't do solar, but usually people use them with solar controllers such as XW SCC60-150. When you get panels, you simply install a charge controller for them and they'll work together. When you get more panels, you buy more charge controllers. The controllers may charge batteries, or their power can be used directly by the inverter. XWs inverters are quite versatile.

XW4548 or XW4024 are basically the same thing just smaller.

Delly wrote: »

There is one thing that come to my mind, with many small system it is easier to control and configure things the way you want. But with this all in one big daddy system, I'm wondering how I can remote control it. With the small setup I was thinking of connecting a zigbee plug into the wall outlet and connecting the battery charger to the zigbee plug. The zigbee will be connected to a router which will give me the access to turning it on or of. I'm not sure if this is the proper wait or if it work at all, but at least that's what I had in mind. For this one, I'm not so sure yet. Does these types of inverter usually have some sort of wifi control?

They recently created a new unit ComBox, wich provides Ethernet Interface, so you can access it from anywhere in the world. You can setup WiFi if you need local wireless function. You can monitor everything. I don't have the unit myself, so I cannot tell you how much you can control, but there are some controlling functions too. Usually, when a system is set up correctly, you do not need to do any control.

BB. · August 2013

Re: Using grid inverters without solar/wind

Delly,

One comment--If you will allow me.

Your sort of moving the goal posts around a bit... If I play "engineer" (why yes, I am really boring at parties--why do you ask

:p):

Delly wrote: »

I thought I did make myself clear somewhere out there. It is not clean heat. The major consumers are: heating, cooking, charging el.car (this one is getting more common). Then there are the every day things such as tv, pc, hair dryer, etc... So the point is not to eliminate 1 thing completely, ie charging car, but reducing the total load by 10-20% AT DEMAND (when needed/critical)

You want to reduce the "total load" by 10-20% ... What is "load". In Engineering/Power Engineering terms there are actually two "power calculations". Sounds pendantic--But it is not if you are working with AC power.

One is the version you are familiar with ... Power = Volts * Amps = Watts ... Multiply by time and you get Watt*Hours (and kWH). This is what you see on your monthly power bill ($0.20 per kWH * ZZZZ kWH per month).

However, for a power/electrical engineer, there is another equally important calculation. That is VAR and kVAR.. Volt Amps Reactive.

This gets into the (pretty complex) math of AC power (alternating current). It turns out the P=VI equation is not complete... The real equation is:

Power = Volts * Current * Cosine (angle between V and I vectors)

Volts and Current are "vectors" and you need to use vector math to make the appropriate calculations. I am not sure of your knowledge level about vector math and electrical engineering.

http://en.wikipedia.org/wiki/AC_power

We can go into the details... But for the moment think of standing in front of a car and pulling on a rope.

If you are in front of the car and pull 100 lbs (Newtons, kGrm, --whatever makes sense to you). The force on the car is:

Force = Pull * Cosine of angle
Force = 100 lbs * Cosine 0 degrees = 100 lbs.

However, if you stand of to the side of the car by 60 degrees, an pull 100 lbs on the rope:

Force = 100 lbs * Cosine 60 degrees = 50 lbs.

The rope still has 100 lbs of Force on it--But only 50 lbs of that is moving the car forward (the other 50 lbs is pulling the car sideways)... If you need to pull the car forward with 100lbs of force, you need 2x the pull or 200 lbs on the rope... So, the rope has to be strong enough to withstand 200 lbs if you are not in front of the car.

Similar with AC power... The current does not always follow the Voltage Sine Wave... With motors (inductors), the current "lags" the voltage.... So what does that mean to a power plant/electrical engineer/electrician/wiring in your home?

Glad you asked.

For heating type appliances (toaster, electric water heater, etc.), the angle between Volts and Amps is 0 degrees and Cosine 0 = 1.0 -- That is "100%" efficient use of the current and the wire's capacity.

By the way Cosine of the angle is also called Power Factor (PF). For standard electric induction motors, PF may be round 0.67. And for many electronic items, PF may range from 0.50 to 0.80 or so (PF >= 0.95 is considered "good" PF).

What that means is that the current into your home may be actually 1/0.70 = 1.43x higher because of poor power factor.

For your home wiring, resistive heat loss is given by:

Power = I²*R
Power increase = (1.43)²= 2.0 times more wasted heat in the wiring

So, you need 2x heavier (wire area) copper wire, larger transformers, heavier power lines, and more current from the generator back at the power plant... This "Apparent" power is real and costs the utility a lot of money.

However, for a home owner/renter, you only pay:

Energy = Volts * Amps * Cosine (phase angle) = VA * PF = Watts

Where, the utility needs to supply:

Apparent Power = kWH / PF

And, for many larger commercial customers in the US, the utility actually measures the power factor and increases the bill by:

kWH per month * 1/worst case PF 15 minute average per month or per year

So--You will find that industries that use a lot of electric motors, they will use capacitor banks to "correct" the power factor and bring it near 0.95 (1.00 is not recommended for various reasons) and reduce their electric bills by 40% or so (typical worst case).

In California Central Valley where there is a lot of electric motors (well pumping, Air Conditioning) in the summer, the utility will turn on "capacitor banks" in their distribution system to reduce kVAR currents in their system.

Depending on the load profile of your homes--It is possible for you to reduce their KVAR currents by 10-20% by installing a capacitor bank (there are companies in the US that do this for commercial installations and even homes--But for homes it is, essentially, a scam because residences do not, yet, pay for poor power factor).

Besides motors, there is another source of poor power factor... Many electronic appliances (and Compact Florescent and LED lighting, use switching power supplies with only draw current at the "Peak" of the voltage cycle (charging high voltage capacitors at the front end of the power supply).

This type of current wave form cannot be "fixed" with a capacitor bank (it is a non-linear current wave form). It requires a new power supply design with "active power factor correction".

Newer computers and electronics are starting to have Active PFC -- And there has been European (and US?) requirements for more than a decade now for PFC on larger appliances.

So--It is possible to measure the loads of a home and, possibly, through the use of appropriate capacitors and new PFC appliances, to achieve your desired results (from a utility point of view) in many older homes (newer homes may have less PF issues). Without the use of AC inverters and Battery banks.

It will not "save" kWHr directly--But it saves kVAR (volt amps reactive) -- And, more or less, allows the power distribution and utility generators to operate "more efficiently) (i.e., instead of standing off to the side of the car, stand back in front of the car and wasting force by pulling to the side).

Measuring Power Factor for a home is a bit more complex than measuring voltage (need current probes/clamps inside the main panel). But, if you are getting "smart meters" in your country (now or in the future)--Many digital meters measure PF/kVAR and can report those to the meter reader/electronically back to the utility--So, you can have an automatically generated data base to see how big of issue it is for your target market.

End of "off thread" discussion.

-Bill

Delly · August 2013

Re: Using grid inverters without solar/wind

Oh god, every time I read one of Bill's replies my head spins around :P Don't get me wrong, I really do appreciate your and everyone else's reply

I'll let it sink a little bit and mean while, I'll try to go through the calculation here step by step so that I'm sure I've understood it right. Btw, what does NAWS mean?

BB. wrote: »

WE have a few European folks here that may be able to make some suggestions on suppliers that are closer to you and will not have additional duties/customs charges.

Will be glad to come in contact with them.

BB. wrote: »

3750 WH / 24 volts = 156 AH battery bank?

156 AH * 24 volt battery bank * 0.85 AC inverter eff * 0.50 maximum discharge = 1,591 WH available capacity at 20 hour discharge rate

I think the battery eff/discharge is accounted for twice now. Here is how I calculated the battery size:
- 750Wh for 2 hrs = 1500Wh/h = 1500W
- 1500/24 = 62.5Ah
- 62.5/(0.80*0.50) = 156Ah.

This means:
156*24 = 3750Wh. As I said, bat+discharge rate are included

BB. wrote: »

You are looking to discharge the battery at 750 Watts for 2 hours (1,500 WH discharge)... That is aproximatly a 4 hour discharge rate. For a flooded cell battery, your C20 capacity is 156 AH, but your C₅ discharge rate may be closer to 128 AH capacity--You might want a larger bank.

Already accounted for. What I originally need was 500Wh for 2hours, but to be on the safe side (due to fast discharging), I've increased it to 750Wh. So far so good right?
Also I'm going for AGM batteries since they are "maintenance free".

BB. wrote: »

225 AH * 10% = 22.5 nominal battery charger recomended (any AC/DC charger output current)

225 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 847 Watt nominal array

Why 29V? Many cheap inverter chargers have a 3 step charging method. Surely the conext has one too, though I must admit I still haven't seen anything about it on their web page. I mean, isn't it better to have one? I'm thinking of using a 15-20% charge rate, if possible

BB. wrote: »

If you are assuming 5 hours a day of sun (this is probably true during summer)... But panel angle, one or two axis tracking, snow on panel/snow on ground, etc. all affect performance.

I would be hard pressed to pick 5 hours for a fixed array in Norway... If you did a full 2axis tracking, I am sure you can do better in summer. I would pick closer to 3 hours for 7 months of "OK" solar

This is not a problem so long they/university are/is aware of it, at least not for a test setup. The sun is up almost nearly 21hrs in summer in Norway, and further north, it is up 24/7. Now ofc it is at a very low angle, but there is still sunlight

BB. wrote: »

750 watt load * 2 hours per day * 1/0.77 panel+controller derate * 1/0.80 batt eff * 1/0.85 inverter eff = 955 Watt panel based on loads

Why would I want the Dc power to go through the inverter when I'm only charging up the batteries? Isn't it smarter to go from PV to CC to battery bank? I mean what's the point in converting the volt from DC to DC just to charge the batteries? wouldn't an MPPT CC fix everything? Yes I know it needs to go though the inverter if I want AC from battery bank, but that shouldn't have anything to do with the charging and PV size??

BB. wrote: »

As good as rule of thumb as any to start... Your charging time will be the AH replaced + 2-4+ hours (2 hours for shallow discharge, 4 hour for deep discharge). For example:
750 watt * 2 hours * 1/0.85 inverter losses * 1/24 volt battery bank = 73.5 AH @ 24 volt consumed

73.5 AH / 22.5 amp battery charger (assuming 10% of 225 AH battery bank) = 3.3 hours of charging (assuming perfect battery)

3.3 hours + 2 hours (10%-20% discharge) = ~5.5 hours charging (shallow discharge) -> I don't understand

3.3 hours + 4 hours (20-50% discharge) = ~7.3 hours charging (deeper discharge) -> I don't understand

Not sure what or where the shallow and deeper discharging come from. Is this the same thing as the float, bulk charging you're talking about?
Can I just simplify it to something like: (used battery capacity in % + 40% of used capacity) / (total battery capacity * charging rate). That is:

73.5 * 1.4 = 103Ah to replace
103Ah/(156A * 0.10A) = 6.6 hours.
Does this make sense?

Also, I'm guessing that any MPPT CC would fit with these inverters, right? I'm looking at some of the cheaper once from morningstar. Well, it depends on the price. Let's say the calculation for the PV size Bill did is correct, exactly what is the minimum inverter do I need for this array and my usual 750wh for 2hrs of load? Surely a 4kwh inverter like the Conext 4024 is way above what is needed?

Need to be working more on my list now... Feeling sleepy now too :grr

PS! That last post of yours, Bill, reminded me of of things I've forgotten! As soon as you mention vectors I was like OMG, now I remember! Not that I'm good at those things though :roll:

Anyways, Thanks a lot for all the help guys!
Delly

BB. · August 2013

Re: Using grid inverters without solar/wind

Hi Delly,

We don't pussy foot around here--We get right into the meat of things.

Delly wrote: »

Btw, what does NAWS mean?

Northern Arizona Wind & Sun -- They are a retailer/distributor of Solar/Renewable Energy products and support hardware located in Flagstaff Arizona. Their website is one we reference a lot when pointing people to hardware/prices/documentation:

http://solar-electric.com/
http://www.solar-electric.com/info.html

Northern Arizona Wind & Sun - Electricity from the sun since 1979

Northern Arizona Wind & Sun
4091 E Huntington Drive, Suite B
Flagstaff, AZ 86004
Flagstaff office: (800) 383-0195 or 928-526-8017
FAX Flagstaff: 928-527-0729
Office hours: 8 AM to 4 PM Arizona Time, Mon-Fri. Closed on most major (federal) holidays.

Welcome To Our Online Store

Northern Arizona Wind & Sun, Inc. has been selling and installing solar electric systems and components full time since 1979. Many of our first projects were installing 30 watt solar panels on hogans on the Navajo reservation, where the nearest power line was often 50 miles away, and so was the nearest paved road. The company was incorporated in 1984. Our sales have grown steadily over the past few years, and we are now one of the largest solar retailers in the US. We have installed and sold thousands of PV power systems for communications, cathodic protection, remote home sites, water pumping, telemetry, and RV and battery maintenance systems. We carry a complete line of photovoltaic equipment for industrial and home systems.

A little history...

Northern Arizona Wind & Sun is a family owned business. Our family has been in Arizona since 1885, aside from a few excursions overseas in WW2 and Vietnam. Most of that has been in the Grand Canyon area, and many of the old timers contributed to the history (and some made history) of that area. We recently turned over nearly all of our family historical material, documents, photos etc. to the University of Northern Arizona. Quite a bit of it is now available on the internet - there is a lot a material, including letters and diaries from Edith Bass, one of the first women to live at the Grand Canyon, and the first white woman to have a child at Grand Canyon. NAU Special Library

The forum is run pretty much "hands off" by volunteers here--With the only requests being that we remain professional and family friendly. And focus on Renewable Energy and Conservation.

I think the battery eff/discharge is accounted for twice now. Here is how I calculated the battery size:
- 750Wh for 2 hrs = 1500Wh/h = 1500W
- 1500/24 = 62.5Ah
- 62.5/(0.80*0.50) = 156Ah.

Technically, you don't account for battery efficiency during discharge... The battery "efficiency" on discharge is already taken into account by the C₂₀, C₁₀, C₅ discharge rates (and reduction in "apparent capacity").

If your load is 750 Watts for two hours--Then battery sizing would be:

750 Watt*Hours * 1/0.85 inverter losses * 1/24 volts * 1 day of storage * 1/0.50 discharge = 147 AH @ 24 volt battery bank

The reason we are "close" but not exact is because you are using a Flooded Cell charging efficiency derating of 0.80, and I am using an Inverter loss factor 0.85 ...

If you were driving a 750 Watt DC load directly, then I would use any "conversion losses".

Also note that 24.0 volt for the battery bank... A battery bank will discharge from ~25.4 volts to ~23.0 volts (towards ~20% state of charge--very dependent on temperature, discharge rate, etc.). So, the actual Amps drawn by the inverter will vary inversely to the battery bank voltage (as battery bank voltage drops, AC inverter current draw increases to supply a "constant power load").

This means:
156*24 = 3750Wh. As I said, bat+discharge rate are included

Sort of--It also depends on how fast the current is being pulled from the battery bank -- We normally assume C₂₀, but if you draw high current to 50% state of charge in 2 hours--Then you need to look at the C₄ battery bank capacity.

Already accounted for. What I originally need was 500Wh for 2hours, but to be on the safe side (due to fast discharging), I've increased it to 750Wh. So far so good right?
Also I'm going for AGM batteries since they are "maintenance free".

That is fine--We would recommend that you run a system at ~66% to 75% of its "capacity" daily to reserve some power for poor weather, growth in loads, occasional heavier loads from guests/kids/etc.

But, we do want to know you Did a 1.5x increase in your estimated power usage--So I don't want to throw in more derating factors.

Why 29V? Many cheap inverter chargers have a 3 step charging method. Surely the conext has one too, though I must admit I still haven't seen anything about it on their web page. I mean, isn't it better to have one? I'm thinking of using a 15-20% charge rate, if possible

Solar/RE charging systems will, for example, will output 60 amps until the Absorb voltage is reached. Then old the absorb voltage for X number of hours (or other terminating condition), then drop to float.

More or less, at 25C, AGM/GEL batteries are charged around 14.2 to 14.4 volts (absorb) and floated around 13.2-13.6 volts (see manuals). AGM/GEL batteries are not usually equalized (in the traditional sense of higher charging voltage for a couple of hours).

Flooded cell are usually charged around 14.5 to 14.8 (sometimes even 15.0 volts) and "equalized" around 15.0 to 15.5 volts ("over charging" the battery bank at ~2.5 to 5.0% rate of charge while checking specific gravity of electrolyte every 30-60 minutes to "bring up" weak cells).

Anyway, for 24 volt battery bank, you would just double the above numbers.

Note that I am usually talking about "constant power" devices... Very typically AC inverters and solar MPPT charge controllers are constant power devices... So, you have to look at the equation P=VI to figure out what the current is at any particular voltage for, say 600 watts of charging energy.

This is not a problem so long they/university are/is aware of it, at least not for a test setup. The sun is up almost nearly 21hrs in summer in Norway, and further north, it is up 24/7. Now ofc it is at a very low angle, but there is still sunlight

Solar panels only harvest energy when the sun is pointing at the panels--When the sun is 60 degrees of angle, then Cosine of 60 degrees = 0.5 -- Or 1/2 of the solar energy is being converted into electricity (vs a tracking panel pointing at the sun).

Also, you may have 21 hours of sun, but ~9 of those hours, the sun is behind the panel and not doing much good (want to "talk" about "bi-facial" solar panels? I am not sure I buy the 50% extra power with bi-facial panels).

750 watt load * 2 hours per day * 1/0.77 panel+controller derate * 1/0.80 batt eff * 1/0.85 inverter eff = 955 Watt panel based on loads

Why would I want the Dc power to go through the inverter when I'm only charging up the batteries? Isn't it smarter to go from PV to CC to battery bank? I mean what's the point in converting the volt from DC to DC just to charge the batteries? wouldn't an MPPT CC fix everything? Yes I know it needs to go though the inverter if I want AC from battery bank, but that shouldn't have anything to do with the charging and PV size??

That equation represented the "entire" power cycle (discharge + charging) so all losses were accounted for in that one equation. And--It really does work out--If you mutliply the solar panel "marketing Watts" * real hour of sun, and take into account all of the losses through the charge controller to the battery bank to the AC inverter to the AC loads--Your system is about 52% end to end efficiency (for flooded cell, for AGM battery bank with 0.90 efficiency, that overall number becomes ~59% effciency)

Not sure what or where the shallow and deeper discharging come from. Is this the same thing as the float, bulk charging you're talking about?

No... Your planning on taking the battery bank from ~100% full to ~50% state of charge--That is a fairly deep discharge cycle--And it will take longer to recharge... More or less, for a first approximation,

The battery will take pretty much as much current as you can supply while it is charging from ~0 to 80% state of charge. From ~80% state of charge to 100% SOC, the battery will be at "absorb voltage" (around 28-29 volts (held there by the charge controller) and the battery will slowly decrease charging current to near zero (to ~2% to ~0.1% rate of charge--when the charging current will plateau, or not go any lower, and the battery is "full").

The terms bulk, absorb, float do change between industries--In Solar RE terms they usually mean (again, not always):

Bulk: Battery charger is outputting maximum available current (current limited, or current regulation)
Absorb: Battery voltage has hit "absorb" set voltage (say 29 volts). Battery charger is now "voltage regulation). Battery will be held there for ~2-6 hours (or until sun sets if solar power). If the battery is only discharge to 80% SOC, the absorb timer may be 2 hours... If the battery has been discharge to 50% or less State of Charge, the battery timer would probably be set to 4-6 hours.
Float: Once battery is "full", the charge controller holds ~27 volts--And if there are DC loads on the battery bank, the charger will attempt to support those loads too by holding 27 volts (voltage regulation).

Can I just simplify it to something like: (used battery capacity in % + 40% of used capacity) / (total battery capacity * charging rate). That is:

73.5 * 1.4 = 103Ah to replace
103Ah/(156A * 0.10A) = 6.6 hours.
Does this make sense?

How accurate do you want your model to be? Lead Acid Batteries are actually "Coulomb Storage Devices" and are near 100% efficient when looked at from an Ampere and Amp*Hour point of view (last 10% or so of charging is less than 100% efficient). So, technically:

73.5 AH / 15.6 Amps = 4.7 hours to recharge the "ideal battery"

But the typical Solar RE charger will hit a "absorb voltage limit" at ~85% of battery state of charge... At that point, the charger enters "Voltage Regulation"/Absorb charging phase and holds 29 volts while the battery slowly decreases accepting current from ~15.6 amps to ~1.56 amps or so (this is the "absorb" time)... That is the 2-6 hour time we talk about to finish the charge.

Also, I'm guessing that any MPPT CC would fit with these inverters, right? I'm looking at some of the cheaper once from morningstar. Well, it depends on the price.

Yes, you can mix/match MPPT (and PWM) charge controllers with different inverters... Some inverter/charge controllers are "systems" so they can have better automation/single point computer/remote interfaces, etc... Schneider and Outback are two companies that sell integratable Inverter+MPPT charge controllers.

Is it worth it to have an integrated system? It can be very nice--But it also can be sort of expensive and you may prefer the functions of a Midnite MPPT charge controller with the Schneider XW Hybrid inverter--Sort of your choice. Both (Midnite CC + Schneider XW or Schneider XW CC + XW inverter) will work well.

PS! That last post of yours, Bill, reminded me of of things I've forgotten! As soon as you mention vectors I was like OMG, now I remember! Not that I'm good at those things though :roll:

Might as well get it out of the way--What is your major/degree in Delly?

-Bill

stephendv · August 2013

Re: Using grid inverters without solar/wind

At risk of repeating my previous reply, if you want to control load shifting then your control system must be able to read data from the inverter and charge controllers in order to make it's decisions. The 2kW Sunny Island will let you read every bit of available data from it, including the battery state of charge from its own internal SoC meter- which I'd guess would be quite an important piece of data if you want to do load shifting.
Similarly, the midnite classic (or Lite) will allow you to read and set all internal values so you can log and act on data like the Voc, the Vmp the current, you can limit the current programmatically and control diversion relays programmatically.
The combination of the two will give you the easiest way to have a programmable setup. I don't believe there is any open way to communicate with Xantrex kit since they use a closed protocol (Xanbus AFAICR). Earlier you mentioned that a requirement is to potentially sell to the grid in the future. Can the conext do that? I know the XW can, but not sure about the conext.

Using grid inverters without solar/wind

Comments

Categories