Inverter to Panel Help

Znode · July 2011

Hello everyone, this is my first post and I'm looking for a little help...

I'm doing a pretty large off-grid solar/wind system. I understand how to do most of the system other than how to get an inverter to a breaker panel. I read a few other posts on here that were facing some of the same issue, however, it seemed as though they had already purchased the inverter, breaker box etc so a lot of it was back fitting issues. I have not purchased the equipment yet, so I'm wondering if anyone has good advice as to which equipment to buy that might make this easiest. As I said I'll be running a bit bigger system with multiple inverters, so just FYI.

Thanks!

Cariboocoot · July 2011

Re: Inverter to Panel Help

Welcome to the forum.

The "multiple inverters" is an instant red flag.
Standard AC breaker boxes have two "legs" for split 240 VAC.
Unless inverters are specifically designed to be "stacked" you can't connect their outputs. You can run one inverter to power one leg and another inverter on the other leg with a common neutral. Some inverters aren't even going to work that way.

This is one of those "what exactly were you planning?" things. If you could supply some further details as to system size and so forth it would help. Larger inverters "hardwire" to AC panels fairly easily.

Znode · July 2011

Re: Inverter to Panel Help

Got ya, well here is the system design idea I got from another website, so I guess I'm not sure what their theory was behind the design (attached)

So your advice would just be to get an inverter big enough to handle the entire load and it should be fairly easy to hardwire it to the panel?

Note: I'm clearly a beginner at this so I apologize for the elementary knowledge and stupid questions

Cariboocoot · July 2011

Re: Inverter to Panel Help

Without some sort of long, detailed explanation of what they're trying to do there I can only say that the diagram is too non-specific to be of any use. Taken at face value, simply tying together the outputs of two generic 4kW inverters is a recipe for having to go out and buy new inverters the moment the power is switched on.

So let's talk about you instead!

What is it you actually want to do? Power a remote cabin in the woods? Get some serious camping power in the RV? Find a way to keep the 'frige running when the lines go down? Knock a few dollars off the monthly electric bill? Experiment with solar power to see how it all works?

It's very important to know what the end goal is. It makes a big difference in system design. Trying to copy someone else's set-up for your use (which may be very different from theirs) will only give you frustration - and a big hole in your bank account.

Znode · July 2011

Re: Inverter to Panel Help

We are trying to power a nice remote cabin with no electric grid anywhere nearby but plenty of space and good conditions for solar and wind power, while trying to maintain the niceties of life, tv, lights, not really any major appliances that take mass amounts at once like a washer/dryer etc.

Cariboocoot · July 2011

Re: Inverter to Panel Help

Znode wrote: »

We are trying to power a nice remote cabin with no electric grid anywhere nearby but plenty of space and good conditions for solar and wind power, while trying to maintain the niceties of life, tv, lights, not really any major appliances that take mass amounts at once like a washer/dryer etc.

That's what I like to hear!

Now the basis of designing any off-grid system is the loads. You've got to get a specific handle on them. Just taking the manufacturers' labels' data isn't going to be accurate. If you've got any of the equipment you hope to use there (or even similar stuff) get a Kill-A-Watt (or equivalent) meter for about $30 and start testing. You want to find out how much power you'll use at any one time (maximum Watts) and how much you're likely to use in a day (total Watt hours). The first number will give you an idea how big of an inverter you'll need. The second will tell you how big a battery bank is required. From that you can determine how much solar panel & what charge controller(s) are needed to recharge.

The First Rule of off-grid living is to reduce your power use as much as possible. Not running a washing machine is good. Leave out anything that heats (like electric kettle). If you're only going to be there part-time, consider a propane refrigerator. There's lots of options for pumping water with less than typical power too. My system, with electric 'frige, uses roughly 2.4 kW hours per day - including running 1/3 HP water pump and 1 HP digester pump as well as computer/satellite set-up, and even the occasional zap of a microwave. Under better circumstances I could use less, but I didn't pick where the cabin is. Icarus is champion low-power user around here; something like 400 Watt hours per day.

BTW, you will inevitably need a back-up generator because the sun doesn't always shine.

Znode · July 2011

Re: Inverter to Panel Help

Well I guess we are a little hypocritical of ourselves in a sense I guess. We've decided to cut out the major appliances that we'd only use once in a while but consume mass amounts of energy at once like the washer dryer, freezer, microwave, stove/oven, and supplement propane burner mini propane oven for when they are necessary, but still would like to be able to watch movies have a few tvs and the like. We hope to be able to move out there at somepoint assuming all goes well. We have not purchased any of the equipment yet which is why I came on here first instead of purchase everything and either A) Find out it doesn't all work together,

Not know what I'm doing, or C) A and b.

So from my calculations, we were hoping to have a system that could produce about 7200 kwh a year, or about 19.72 kwh a day, which I realize to the minimalist may sound a bit egregious, but it is what we want. These are of course from the mfg's ratings and not a meter like you suggested.

The system we were thinking of includes 5 600 watt wind turbines, and 3 sets of 1300 watt solar panels.

Cariboocoot · July 2011

Re: Inverter to Panel Help

Smart move. Especially not buying anything before finding out what you need.

A word about wind turbines: don't.
Most often a site won't support them. They like sustained winds in the 20 mph range. No gusts and gentle breezes don't produce any power. The second problem is that they are usually installed wrong. They really want to be up in the air with nothing about to cause turbulence. The tower systems often cost more than the turbine. The third problem is that, quite frankly, most of the small wind systems are junk and don't produce anyplace near the rated capacity. They tend to be a bad investment all around. You can read through the wind power section of the forum and see these problems come up over and over again.

Propane is your friend for stove/oven, hot water, and anything else you need to heat. For occasional use a propane 'frige is more practical than an electric one. But with your planned consumption ...

It's not that 19 kW hours per day can't be done, it's that it would be very expensive and probably not necessary. A big screen TV (LCD) can use <200 Watts if you set the screen right (reduce brightness). You may find that you actually will use about 1/4 to 1/2 your expected 19 kW hours.

Just as an example, though, you'd be looking at a 48 Volt system for that much stored power (upping the system Voltage eases handling the current involved in higher power systems). It would require at least 792 Amp hours of battery, which is quite large. You'd probably have to go whole-hog with a 1000 Amp hour, 2 Volt cell set-up. You're looking at $3,000 worth of batteries there. The inverter would be another $2,000 - $3,000. Got "sticker shock" yet? How about $20,000 just for the 7400 Watt array? And two charge controllers. That should impress upon you the need to reduce consumption as much as possible; this stuff is expensive.

BB. · July 2011

Re: Inverter to Panel Help

Let's say you are near/have weather similar to Billings Montana.

Using PV Watts, for an off-grid system, 3.9 kWatt array, and 0.52 overall system efficiency, we get:

"Station Identification"
"City:","Billings"
"State:","Montana"
"Lat (deg N):", 45.80
"Long (deg W):", 108.53
"Elev (m): ", 1088
"PV System Specifications"
"DC Rating:"," 3.9 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 2.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 45.8"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 7.9 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.25, 210, 16.59
2, 4.17, 241, 19.04
3, 5.22, 324, 25.60
4, 5.27, 301, 23.78
5, 5.76, 331, 26.15
6, 5.99, 319, 25.20
7, 6.56, 356, 28.12
8, 6.31, 346, 27.33
9, 5.88, 321, 25.36
10, 4.78, 285, 22.52
11, 3.62, 221, 17.46
12, 3.03, 196, 15.48
"Year", 4.99, 3452, 272.71

You will get around 200 to 300+ kWH per month from your array. Or about 3,425 kWH per year.

19.72 kWH per day * 30 days per month =592 kWH per month

During winter, your array should be ~3x larger (actually even larger since you cannot really use an "average" amount of kWH per day because solar, and wind, is variable)--You will have to make a fair amount of usage with a genset.

Normally, for a "cost effective" off grid system, people should aim at about 100 kWH per month as a starting point (or ~3.3kWH per day).

Not to say you cannot build a system that large--but it will not be inexpensive... Plus remember that batteries need to be replaced every 6-15 years or so... and the electronics have around a ~10 year useful life before they need to be replaced (basically, it gets very difficult to get spare parts for electronics in general that are over 10 years old).

For most people, grid/utility power costs around $0.10 to $0.20 per kWH or so...

For off grid systems, the estimated power costs are in the range of $1-$2+ per kWH (cost of hardware, batteries, and replacements over a ~20 year system life--no taxes, no cost of capital).

If you knew your off-grid power is ~10x what you are spending grid power today--what would you do different?

You might look for poster "Mangas" here--He has a pretty large off-grid system in the South West that he even uses with Air Conditioning... From his signature:

Off Grid 4x5500SW Plus Xantrex SinePlus Inverters/48V DC System/44x185W Sharp Panels/64xTrojan L16-REB 6v/Desulfators/2xOutback FlexMax 80s'/Water Misers/Temp Sensors/Interfaced Air Extractor System/Output to 2x100Amp AC Service Panels/Two 2.5 Ton Central A/C Units/RASTRA Construction

Click on his name and click on threads that he has started--And you can see some of his design.

Regarding wind turbines--Do a lot of research on them... Personally, I am not a big fan of wind turbines (I think they cost a lot, are not usually very mechanical reliable, and do not generate much energy for most installations due to various reasons). I would suggest designing your system for PV Array at least 9 months of the year, and a back up genset to help with the other 3.

At that point, you can add in small wind and, hopefully, it will reduce your generator runtime.

-Bill

BB. · July 2011

Re: Inverter to Panel Help

I should add, we have a thread with random Solar Related information and projects.

Working Thread for Solar Beginner Post/FAQ

You might want to look at solar thermal projects... They can be really useful for generating heat and some hot water even for homes in the snow belt.

Solar Thermal can be a nice source for space heating and hot water... And usually is "cheaper" per kWhr/BTU vs Solar PV Electric. Also, Solar Thermal lends itself very well to do it yourself projects. Note, these are plumbing projects and have their own issues (leaks, pump failures, installation issues trapping air, anti-freeze, storage, heat exchangers, etc.):

Solar Shed and other Solar Thermal Links

A good place to start reading is Home Power Magazine... They have a free past issue online--and have a lot of articles you can read for free. I don't always agree with them and their reviews--but they are a fun and enlightening read:

Home Power Mag

If you need A/C or find fuel is very expensive to bring to your place--You might look at A/C Mini-split "Heat Pump" systems. They can be a significant source of heat, even in winter, if you have enough electrical energy.

-Bill

Znode · July 2011

Re: Inverter to Panel Help

Great information. That is kind of what I was worried about. The product reviews for the "consumer" turbines are pretty poor and read pretty similar to what you just said. For whatever reason that worries me, like any portfolio typically diversification is your friend, that was a key reason I wanted to use both. Not to sound arrogant or what have you, the money isn't really much of an issue none of those numbers really shock me after the research I've done, especially since power out there is more of a "luxury" for us rather than a means to conserve.

Znode · July 2011

Re: Inverter to Panel Help

BB. wrote: »

If you need A/C or find fuel is very expensive to bring to your place--You might look at A/C Mini-split "Heat Pump" systems. They can be a significant source of heat, even in winter, if you have enough electrical energy.

Yeah wow those are pretty cool I didn't know about those thanks.

Maybe it would be more cost efficient to just hire 25 ppl or so to ride a "Pedal a Watt" 24 hours a day? lol

BB. · July 2011

Re: Inverter to Panel Help

Znode,

That is fine--We all here recognize that power usage is a highly personal choice and we are here to help educate folks so they can make their own decisions.

So--From a practical point of view:

Conserve (lots of insulation, energy start appliances, turn off unneeded items, etc.).
Measure your loads (peak watts, Watts*Hours per day usage)
Define your needs (12 month, 9 months, seasonal, weekend, etc.)
Design system on paper (probably several different options)
Then you are ready to do buy/build your system/home.

Note that, in general, electrical systems do not scale up (or down) very well... If you are off by a factor or 2x or greater--many times you almost have to start over with the major components.

For your system--It sounds like the Schneider/Xantrex Hybrid Inverter system would be a good start... Their largest "home system" is 6kW on a 48 volt battery bank. Supplies 120/240 volt split phase AC (typical home power).

From a design point of view--focus on the loads, inverter, and the Battery Bank first... Pretty much, the battery bank is the heart of your system--and the rest of the "parts" are there to keep your battery bank "happy".

One person leaving a heavy load on over a week trip during bad weather (heater, well pump, etc.) that takes the battery bank dead once--and you are out many $k of batteries.

Everything else is fairly rugged and forgiving.

-Bill

BB. · July 2011

Re: Inverter to Panel Help

Znode wrote: »

Maybe it would be more cost efficient to just hire 25 ppl or so to ride a "Pedal a Watt" 24 hours a day? lol

Been down that road here in at least one or two threads.

generator bike system
New User, New Question: self generated power

-Bill

Znode · July 2011

Re: Inverter to Panel Help

Cariboocoot wrote: »

Just as an example, though, you'd be looking at a 48 Volt system for that much stored power (upping the system Voltage eases handling the current involved in higher power systems). It would require at least 792 Amp hours of battery, which is quite large. You'd probably have to go whole-hog with a 1000 Amp hour, 2 Volt cell set-up. You're looking at $3,000 worth of batteries there. The inverter would be another $2,000 - $3,000. Got "sticker shock" yet? How about $20,000 just for the 7400 Watt array? And two charge controllers. That should impress upon you the need to reduce consumption as much as possible; this stuff is expensive.

Thanks for the example. I assume I would also need some quantity of combiners for that big of array? Also, how do you figure 2 charge controllers? And I assume, as part of my original question, that these bigger inverters have just a standard output vs the little "three prong" output?

:cool:

Cariboocoot · July 2011

Re: Inverter to Panel Help

Znode wrote: »

Thanks for the example. I assume I would also need some quantity of combiners for that big of array? Also, how do you figure 2 charge controllers? And I assume, as part of my original question, that these bigger inverters have just a standard output vs the little "three prong" output?

:cool:

An array that size would no doubt have multiple strings of several panels (perhaps four) combined in parallel. That's definitely combiner box and fuse/breaker territory. Four 250 Watt panels, for instance, would be 1 kW per string and you'd need seven. You probably wouldn't do it that way, though. It would take some time to work out a configuration that both meets your needs and is commercially available.

The two controllers would be required because about the biggest one you can get is the Outback FM80, which handles 80 Amps max. A 1000 Amp hour battery bank would need a potential 100 Amp charging rate, which can't be accommodated on a single controller.

The bigger inverters have standard wiring knock-outs and terminals for accepting ordinary household wire for both AC out and AC in.

Again, I see a real need here for reevaluating the loads. Most of the time my system runs under 200 Watts. If you ran 500 Watts (big movie system) ten hours a day that's only 5 kW hours per day. With a little careful calculation you could have all the toys and not have to spend a truck load of money on a system.

BB. · July 2011

Re: Inverter to Panel Help

Sizing the array is one of the last steps... It depends on what charge controller(s) you want, what brand/model of panels is the best $$$/watt shipped to your place vs Vmp/Imp configuration to meet your charge controller needs and wiring requirements.

Even if you picked the "optimum" controller+panels+wiring configuration now--Those panels may not even be available in 6 months, or some other panels at 1/3rd the cost are now available.

It is really a wacky/changing world right now in Solar Panels (and to a lesser degree, the electrical equipment too).

The larger inverters you would just wire then to a "main AC panel" and from there, wire your home as normal (120/240 VAC if you choose that voltage setup).

There are a lot of choices to be made--but without nailing down your power needs--we end up shotgunning the problem and probably confusing each other about the end goals.

The rules of thumb (cost of power, cost of system) based on generic numbers is usually close enough for you to identify how much generating power is worth to you...

Some people do run Microwave ovens and larger computers on relatively small off-grid systems... It is usually the continuous power usage (12 hours or 24 hours per day) that really drive system design (battery capacity, solar array capacity).

The inverters and charge controllers are relatively inexpensive. You can up-size or down-size based on your needs pretty easily (i.e., slow well pump--low power running many hours a day, vs a large well pump that only runs tens of minutes per day).

Until we have a better handle on your loads--we are going keep asking questions you cannot answer--and making guesses that may, or may not, meet your needs.

-Bill

Cariboocoot · July 2011

Re: Inverter to Panel Help

BB. wrote: »

Some people do run Microwave ovens and larger computers on relatively small off-grid systems... It is usually the continuous power usage (12 hours or 24 hours per day) that really drive system design (battery capacity, solar array capacity).

Hey! I'm one of them people!

Switching out the desktop(s) (Yes, sometimes two) for laptop knocked 100 Watts easy off the loads. Over usually 6 hours of use - there's 600 Watt hours savings right there. Or more power than Tony uses for his whole house. :roll: When you use things can make a difference too: for instance I switch the water pump on at "Float" and fill a big pressure tank which then provides the day's water. Otherwise the potential energy the panels are capable of harvesting would go wasted.

I mention it to point out that loads can be tailored to meet lifestyle choices and yet not consumer vast quantities of very expensive electric.

jaggedben · July 2011

Re: Inverter to Panel Help

Just a quick comment that solar hot water should be considered too. It can be put in line with tankless water heaters, such that the gas heater only kicks in when it has to. Can allow you to be much less dependent on propane for taking showers.

Znode · July 2011

Re: Inverter to Panel Help

Alright well here is the break down of all of my electric items, as rated by the manufacturer's at least so I don't know if this will help at all:

4 120 W LED Ballasts (24 hrs a day) = 11.52 kwh

25 7 W LED bulbs (10 hrs a day) = 1.75 kwh

Solar Fridge 198 Watts a day = .198 kwh

200 W Air Filter (24 hrs a day) = 4.8 kwh

3 LCD TVS @ 200 W (8 hrs a day) = 4.8 kwh

So if my calculations here are correct, that would be a total of 23.068 kwh a day. So is that at all helpful or what other information would you need from me to be able to give info that isn't guessing?

Cariboocoot · July 2011

Re: Inverter to Panel Help

How many people will be living there that you need three TV's on for 8 hours a day?

Those LED light numbers seem rather high, but I don't know because we can't get LED lights here outside of Christmas strings, nightlights, and a few very expensive bulbs that don't fit anything I've got.
How necessary is that air filter?

You have to question the need and and consumption of everything you're going to run to see if it can be eliminated or reduced. Or you spend $80,000 on a system. (That just goes against every cheapskate bone in my body!

)

Znode · July 2011

Re: Inverter to Panel Help

There could be upwards of 10 people there at a time, that's why those numbers are the max that I would like to be able to have. The air filter and LED ballasts are 100 % necessary, the other items can and will fluctuate

BB. · July 2011

Re: Inverter to Panel Help

Where will the home be located (Billings close)? Are you planning on 12 months a year, summer or winter only use, etc.? Weekend at a time, full time occupation?

TV's--dvd player, satellite receiver, DVR's, etc.?

-Bill

rplarry · July 2011

Re: Inverter to Panel Help

I agree with Coot, those LED numbers sound awfully high. I am wondering if maybe the 120 watt listing is maybe the amount of watts the ballasts are capable of producing, not what they consume. This is where a Killawatt meter could save you some big bucks.
Larry
PS YOur 1.75KW for the LEDs should be .175kw. Also I don't see any computers, Sat recievers, Microwave ovens, radios, DVD players, power tools, etc. on you list of electrical consumers.

BB. · July 2011

Re: Inverter to Panel Help

Actually, that is correct based on 25 lights x 7 watts x 10 hours per day or 1.75 kWH per day...

-Bill

Cariboocoot · July 2011

Re: Inverter to Panel Help

Based on the information provided, this is what I see:

As much as 1500 Watts used at any given time. Easily met with any 2 kW or larger inverter.
23 kW hours per day, call it 24, means definitely a 48 Volt system at 500 Amp hours. This means a minimum 1000 Amp hour batter bank. If you want to limit the DOD to 25% instead of 50%, that number (and subsequent calculations based on it) needs to be doubled. Forklift/industrial batteries could work here, but remember that they are heavy (difficult to locate/move) and expensive.
That size battery bank you'll want to make that 10% peak current potential for sure, as it is likely to be tall-case 2 Volt cells. Looking for about 60 Volts @ 100 Amps you get 6 kW of panel. Factor in the "typical" 77% efficiency rating and you have 7792 Watts of array - just for starters.
You will also need to consider your location and how that affects solar output (the above "guestimate" is based on getting good sun), distance between arrays and charge controllers (V drop factor), and ambient temperatures.

Are we making any progress?

Znode · July 2011

Re: Inverter to Panel Help

Well I understood half of that so that is progress I guess.

So your talking about something along the lines of---> http://www.solar-electric.com/trl111ah2dec.html , and 24 of them to build the battery bank you mentioned?

BB. · July 2011

Re: Inverter to Panel Help

Regarding the Trojan 2 volt 1,110 AH cell... Yes and no...

Yes, suggesting larger single cell (or multi-cell batteries like Forklift) in series vs a bunch of smaller batteries in parallel.

However, the Trojan 2 volt 1,110 AH battery is actually 3x 2volt x 370 AH cells in parallel. Three battery caps, three cells to fill, three cells to monitor SG in...

Ideally, if it was one cell with one filler--would have been a "better" battery. Certainly, it reduces your cell to cell wiring to internal to the battery.

The other issue with battery AH vs voltage vs size... Do you have a small crane or forklift handy plus flat concrete surface to move the batteries around on--Or do you have stairs down into a basement and have to hand carry each cell/battery.

The 2 volt cells allow you to build a big bank with only series connections (or at least fewer parallel connections which are a bit more probalamatic) with cells you can move around with two people.

Otherwise, you can look for large 12/24/48 volt battery banks used in forklifts (aka traction batteries) that you can move with a forklift or crane. The traction batteries can last 15-25 years--but they do have larger self discharge and lower efficiency (especially as they age)... Your solar array and battery charging needs to be significantly larger to keep those large/lossy batteries happy (closer to the 10-13% rate of charge vs closer to the 5% minimum which AGM's will be "OK" with). At the very least, your array for flooded cell vs AGM should be a minimum of 20% larger to account for the self discharge of older battery banks.

Bill

Cariboocoot · July 2011

Re: Inverter to Panel Help

Znode wrote: »

Well I understood half of that so that is progress I guess.

So your talking about something along the lines of---> http://www.solar-electric.com/trl111ah2dec.html , and 24 of them to build the battery bank you mentioned?

Yes, the Trojans are one choice. Crown also makes some high-capacity 2 Volt cells: http://www.solar-electric.com/2voltbatteries.html So does Surrette: http://www.solar-electric.com/2voltbatteries1.html
You could also pick a couple of industrial battery like this: http://www.solar-electric.com/crinba24vo10.html They will take a deeper discharge (80%) and tend to last longer. A bit pickier on maintenance.

Znode · July 2011

Re: Inverter to Panel Help

Yes to flat concrete and small fork lift

BB. · July 2011

Re: Inverter to Panel Help

Some people here have been very happy getting used ForkLift batteries...

Search for thread by "adas" -- He built a large off-grid fabrication business around used / rebuilt forklift batteries.

At least at first until you have your system/power needs dialed in--then you can replace with other batteries sized to your usage.

-Bill

PS: Would still like to know where the home will be located (aproximatly nearest large city if not Billings)... Also, is this a 12 month, 9 month, seasonal, weekend place?

Inverter to Panel Help

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