MPPT's working

drraptor

Re: MPPT's working

BB. wrote: »

You can connect the panels in parallel or series--The Vmp and Imp are within 10% of each other.

What is the battery voltage? What is the maximum input voltage rating of the charge controller?

But the 150 watt panel seems closer to a 108 watts--not 150 watts based on the numbers you supplied. Are the ratings correct?

-Bill

MPPT is rated as 20A and Max input as 100V. Battery 12V. I want to connect in Series ( increased voltage) due to the length of wire (50ft) btw charger and panels.


The rating for 150W panel might be wrong.

drraptor

Re: MPPT's working

Cariboocoot wrote: »

You still do not need to put a diode in anywhere.

A 25/30A fuse will do ?

are there any special fuses for DC systems ?

BB.

Re: MPPT's working

Technically, with any protective device, you need the maximum operating voltage and maximum interrupt current ratings. (and add: the fuse/breaker/cabling should typically, at least, be 1.25x larger than the maximum continuous current you intend to support).

As you go above ~24 volts DC, the number of fuses/breaker options go down.

Also, remember you are looking at lead acid batteries that can output 100's to 1,000's of amperes (or more) into a dead short.

Our host NAWS, has quite a selection of fuses/breakers:

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

They are scattered around a bit--Some generic locations and some specifically made/supplied by Midnite Solar.

For a simple and small fuse holder, Blue Sea makes a very nice ones (fuses sold separately) that can bolt to a battery or bus bar:

Attachment not found.Attachment not found.

-Bill

drraptor

Re: MPPT's working

BB. wrote: »

Technically, with any protective device, you need the maximum operating voltage and maximum interrupt current ratings. (and add: the fuse/breaker/cabling should typically, at least, be 1.25x larger than the maximum continuous current you intend to support).

As you go above ~24 volts DC, the number of fuses/breaker options go down.

Also, remember you are looking at lead acid batteries that can output 100's to 1,000's of amperes (or more) into a dead short.

Our host NAWS, has quite a selection of fuses/breakers:

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

They are scattered around a bit--Some generic locations and some specifically made/supplied by Midnite Solar.

For a simple and small fuse holder, Blue Sea makes a very nice ones (fuses sold separately) that can bolt to a battery or bus bar:

Attachment not found.Attachment not found.

-Bill

Thanks so I should use http://www.bluesea.com/products/category/Fuse_Blocks/Terminal_Fuse_Blocks with a 25A fuse (1.25x20).

BB.

Re: MPPT's working

If the MPPT controller has a "hard output limit" of 20 amps--then 25 amps is fine. If the MPPT controller (and solar array) could output more current--Then I would go with 10 AWG wire and 30 amp fuses.

-Bill

MPaulHolmes

Re: MPPT's working

NorthGuy wrote: »

You can increase the precision by averaging a higher number of samples. If you do avearging with precision of 1/10th of a tick or even 1/100th, it will make it much smoother.

You probably don't need to do full sweeps all the time. You can do it once in the beginning. Once you locate the peak, the best strategy is to sit around the peak. You can do a point slightly to the left of where you are. If it is better than where you are, you move to that point. If not, you do a point to the right. If you're close to the peak, it'll work great.

I did one test with the new high resolution. You can see it near the bottom (it was at like 7:30AM on the next day):


Then I tried to implement your strategy for the MPPT and that worked awesome! Here's a picture of that at around 4:30PM with all the panels connected. They y axis is in Watts, x axis in seconds. I'll double check the results, but it looks pretty dang efficient:

drraptor

Re: MPPT's working

what are specification and numbers of Panels you are using ?

MPaulHolmes

Re: MPPT's working

I've got a total of 20 280w panels, open circuit voltage of 45v, maximum power voltage of 35.9v, 8.2amp (I think) short circuit current. I've got 4 separate strings of 5 panels per series string. I've got a box next to the panels that lets me remove or put back into the circuit any of the four parallel strings easily.

They are all ground mounted at about a 70 degree angle, facing the south with no obstructions. Smack dab in the middle of the Sonoran desert. haha. I would have tried to make some sort of tracker, but everyone keeps warning me about the monsoons that are coming, so I chickened out.

NorthGuy

Re: MPPT's working

MPaulHolmes wrote: »

Then I tried to implement your strategy for the MPPT and that worked awesome!

The real test will come when you see rapidly changing sun and clouds, although it probably doesn't happen very ofthen in Sonoran desert.

drraptor

Re: MPPT's working

drraptor wrote: »

Can I connect the following panels on a 20A VOC 100V MPPT.

Polycrystalline / Monocrystalline.
Watt 150 / 100
VOC 22 / 21.6
ISC 7 / 6.43
Vmp 18 / 17.2
Imp 6 / 5.81

An update. ISC for 150 watt is >7.98 how can I measure IMP without a charge controller ?

Photowhit

Re: MPPT's working

You could use a clamp meter on the incoming cable from the panel, while the system is 'bulk' charging, but that is a momentary test under whatever conditions you have. Though heat effects IMP less than other things like panel angle to the sun, length and thickness of cabling...

drraptor

Re: MPPT's working

Photowhit wrote: »

You could use a clamp meter on the incoming cable from the panel, while the system is 'bulk' charging, but that is a momentary test under whatever conditions you have. Though heat effects IMP less than other things like panel angle to the sun, length and thickness of cabling...

No charge controller I can't connect the batteries, instead I used a DC fan (like the one used in car radiators ) as a Load. the current went upto 6A (under cloud cover). but voltage also dropped to 8V

Cariboocoot

Re: MPPT's working

Actually you can not measure Imp even with a charge controller; just whatever current happens to flow from the panels to the batteries.

For testing current flow to a 'direct' device such as your fan you'd do the same as Photowhit said; clamp-on DC Ammeter.

You may also want to test the Isc (current short circuit) to be sure the panels are capable of putting out sufficient current for the fan. You do that the same way, only instead of connecting to the fan you short the panel leads together (no, it won't hurt anything). If you can't get close to full Isc then there probably isn't sufficient insolation on the panel (wrong angle, bad weather, shading, et cetera). Check that you have this power potential first, then see if the fan runs properly.

It is normal for Voltage from the panels to drop when current is being drawn. Basically you get Voc (Voltage open circuit) with no load on - and there will be no current. Connect a load and the Voltage goes down, current comes up. They will always try to produce the current 'first', so you can see Imp and substantially lower output Voltage than Vmp. The maximum power is achieved at Imp * Vmp.

drraptor

Re: MPPT's working

Cariboocoot wrote: »

Actually you can not measure Imp even with a charge controller; just whatever current happens to flow from the panels to the batteries.

For testing current flow to a 'direct' device such as your fan you'd do the same as Photowhit said; clamp-on DC Ammeter.

You may also want to test the Isc (current short circuit) to be sure the panels are capable of putting out sufficient current for the fan. You do that the same way, only instead of connecting to the fan you short the panel leads together (no, it won't hurt anything). If you can't get close to full Isc then there probably isn't sufficient insolation on the panel (wrong angle, bad weather, shading, et cetera). Check that you have this power potential first, then see if the fan runs properly.

It is normal for Voltage from the panels to drop when current is being drawn. Basically you get Voc (Voltage open circuit) with no load on - and there will be no current. Connect a load and the Voltage goes down, current comes up. They will always try to produce the current 'first', so you can see Imp and substantially lower output Voltage than Vmp. The maximum power is achieved at Imp * Vmp.

So I can't be sure except by taking this to a certification facility such PCSIR http://en.wikipedia.org/wiki/Pakistan_Council_of_Scientific_and_Industrial_Research ?

drraptor

Re: MPPT's working

what is a "Grid-Interactive" Inverter does it uses both Grid and Solar to charge the battery Bank ? What difference btw Grid-Interactive and Grid-tie

Cariboocoot

Re: MPPT's working

drraptor wrote: »

what is a "Grid-Interactive" Inverter does it uses both Grid and Solar to charge the battery Bank ? What difference btw Grid-Interactive and Grid-tie

Grid-tie refers to the standard panels-to-inverter-to-grid system; it has no battery back-up and only outputs power when the panels are energized.

Grid-interactive refers to a system with batteries which also connects to the grid and may either sell surplus solar back or act solely as a back-up power source with solar recharging (such as is often used in places where the grid is unreliable).

To accurately measure a panels' Imp you need to be able to control the light on it, the operating temperature, and the resistive load across its output. It's pretty much a lab job, and even then you get the famous STC ratings which are not absolute in the real world.

drraptor

Re: MPPT's working

Cariboocoot wrote: »

Grid-tie refers to the standard panels-to-inverter-to-grid system; it has no battery back-up and only outputs power when the panels are energized.

Grid-interactive refers to a system with batteries which also connects to the grid and may either sell surplus solar back or act solely as a back-up power source with solar recharging (such as is often used in places where the grid is unreliable).

To accurately measure a panels' Imp you need to be able to control the light on it, the operating temperature, and the resistive load across its output. It's pretty much a lab job, and even then you get the famous STC ratings which are not absolute in the real world.

Thanks.
is Grid-interactive same as Hybrid ? also how can you switch between it acting as solely as a back-up power source and dumping the output to grid ?

BB.

Re: MPPT's working

From what I understand (remember, I suck at definitions/English) Grid Interactive is the same as Grid Tied Inverters... GI appears to be the "official" term.

"Pure" GT or GI inverters are those that do not have Battery power for backup... The GT/GI inverter simply takes the solar power power (or wind/water turbine power systems are available too) and converts it to AC power to dump into the AC power lines.

Hybrid inverters are those that run off a battery bank... They Hybrid inverter has an AC output that goes to a separate sub panel ("protected" power--i.e., always AC power available). And he Hybrid Inverter also has an AC power input for connection to the grid (may have an AC2 input for AC generator backup too).

In "normal" operation, the Solar panels "charge" the Battery Bank, and the hybrid inverter operates in GT/GI mode--Taking any excess power from the battery bank (i.e., tries to hold the battery bank at "float" voltage) and shoves power out the AC input to the utility (just like a normal GT inverter would).

If the AC power fails, the Hybrid inverter disconnects from AC power and changes to "Off Grid" mode. It now takes battery power and inverters it to AC power for operating any loads on the protected sub panel.

The "modern" AC Hybrid inverters are pretty straight forward to install--But have some pretty complex operating modes (beside the above, they may have an internal battery charger, fail over to backup AC generator, and even the ability to run "generator support" -- Share power with the AC generator and solar array).

The Schneider Hybrid Inverter is used both for grid connected homes and pure off grid homes--The Hybrid function does not add that much to the overall system price.

-Bill

drraptor

Re: MPPT's working

What we need is such a inverter which doesn't dump any AC power to grid. Instead, it should Use both grid and Solar Panel to provide AC power to local circuit. With Solar Panels acting as a source in case of power failure.

BB.

Re: MPPT's working

drraptor wrote: »

What we need is such a inverter which doesn't dump any AC power to grid. Instead, it should Use both grid and Solar Panel to provide AC power to local circuit. With Solar Panels acting as a source in case of power failure.

And this is where it gets "complicated"... There are not many (if any) AC inverters that will do Hybrid mode and not feed power back to the utility. The Schneider XW hybrid inverter seems to draw a 100-200 watts or so from the grid to make sure that back feed does not happen (runs up your Grid power bill even if you have enough solar).

And, you will need batteries for backup AC power--So you have the expense and losses of a battery bank--Which adds a lot to the costs of a backup/emergency off grid system (SMA has a new pure GT Inverter that will supply something like 10 amps of AC voltage just from the solar array--But that requires enough sun and will not supply any AC power if it is very cloudy/nighttime).

-Bill

mtdoc

Re: MPPT's working

BB. wrote: »

From what I understand (remember, I suck at definitions/English) Grid Interactive is the same as Grid Tied Inverters... GI appears to be the "official" term.

"Pure" GT or GI inverters are those that do not have Battery power for backup... The GT/GI inverter simply takes the solar power power (or wind/water turbine power systems are available too) and converts it to AC power to dump into the AC power lines.

Hybrid inverters are those that run off a battery bank... They Hybrid inverter has an AC output that goes to a separate sub panel ("protected" power--i.e., always AC power available). And he Hybrid Inverter also has an AC power input for connection to the grid (may have an AC2 input for AC generator backup too).

Bill,

I believe Outback uses the term " Grid Interactive" to describe their "Hybrid Inverters". See HERE. In fact, I think they may have invented the term - though I'm not sure - I just recall seeing that term used first in their literature for their "G" inverters. Outack does not sell any grid tie only inverters. I know I, and I think many others take "Grid Interactive" "Hybrid" "Grid tie with battery back-up" to refer to basically the same thing. Obviously AC coupling is another wrinkle that allows incorporation of strict grid tie inverters into a back up system as well -something that both SMA and Outback systems can do. (I;m not sure about Xantrex)

And this is where it gets "complicated"... There are not many (if any) AC inverters that will do Hybrid mode and not feed power back to the utility. The Schneider XW hybrid inverter seems to draw a 100-200 watts or so from the grid to make sure that back feed does not happen (runs up your Grid power bill even if you have enough solar).

Actually all the Outback G inverters can do this - with the the "Sell RE" feature easily turned off. They have a full idle power draw of about 20 watts (6 watts in search mode). Do the XWs really draw 100-200 watts at idle?

BB.

Re: MPPT's working

As I understand (not that I understand much), the XW are not drawing idle current--It is just their present control loop's ability to ensure that it never back feeds the utility (i.e., margin of error for 6-12 kW output would be greater than 2% accuracy of their measurements/ability to control/react to changing loads--certainly believable).

I know nothing about the design or the details of there product--Just relating one other person's experience here and guessing at the reasons why.

Years ago, when we were qualifying the power factor on a new (back then) AC power supply with power factor correction. In order to meet the specifications (there was a limit to how much "surge noise" we could have--don't remember the details now), we ended up with "issues" of varying loads on the switching power supply.

A digital computer (and disk drives) can have very quickly changing current requirements (accessing memory, seeking disk drives, etc.)--So even though the power supply would meet specifications based on driving a constant load, the "surge noise" could get down to the 1 to 1/2 AC cycle range and violate the current vs voltage wave forms--i.e., instantaneous PF could appear to be less than specification, i.e., a 1/2 cycle in, more current demand and power supply "steps up" current draw in middle of an AC voltage cycle and instantaneous PF would "look wrong"--Which would violate the requirements. As I recall, we just punted and found that the randomness of dozens of processors and disk drives "averaged out" so that the supply current requirements were stable enough to pass the tests.

I could imagine the control loop issues if a multi-kW heater or motor load was cycled off--And the Hybrid inverter had to reduce output current "instantaneously" and not drive any power back to the grid. There are engineering requirements and there are legal requirements--And they don't always agree or make sense when the two meet.

-Bill

BB.

Re: MPPT's working

From UL:

1.1 These requirements cover inverters, converters, charge controllers, and interconnection system equipment (ISE) intended for use in stand-alone (not grid-connected) or utility-interactive (grid-connected) power systems. Utility-interactive inverters, converters, and ISE are intended to be operated in parallel with an electric power system (EPS) to supply power to common loads.

1.2 For utility-interactive equipment, these requirements are intended to supplement and be used in conjunction with the Standard for Interconnecting Distributed Resources With Electric Power Systems, IEEE 1547, and the Standard for Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems, IEEE 1547.1.
1.3 These requirements cover AC modules that combine flat-plate photovoltaic modules and inverters to provide AC output power for stand-alone use or utility-interaction, and power systems that combine other alternative energy sources with inverters, converters, charge controllers, and interconnection system equipment (ISE), in system specific combinations.
1.4 These requirements also cover power systems that combine independent power sources with inverters, converters, charge controllers, and interconnection system equipment (ISE) in system specific combinations.
1.5 The products covered by these requirements are intended to be installed in accordance with the National Electrical Code, NFPA 70.

Probably their term is Utility Interactive... I would have tended to shy away from that term because U.I. is also a very common acronym for "User Interface"--Which could cause even more confusion (...on your UI Inverter, go to the UI on the UI Inverter interface box and configure the...).

-Bill

Don't even want to go into what "Grid Connected" would mean... That covers anything that is plugged into an AC outlet.

mtdoc

Re: MPPT's working

BB. wrote: »

Probably their term is Utility Interactive...

Outback's term actually is Grid Interactive. It is the term used - and the title in large bold print of the link I provided. I don't disagree that it may not be the best term to use but it is the one they've been using for years. It's the term that's been all over their G inverter literature for years. Here's the front page of their GVFX/GTFX programming manual:

Attachment not found.

mtdoc

Re: MPPT's working

BB. wrote: »

I could imagine the control loop issues if a multi-kW heater or motor load was cycled off--And the Hybrid inverter had to reduce output current "instantaneously" and not drive any power back to the grid. There are engineering requirements and there are legal requirements--And they don't always agree or make sense when the two meet.

-Bill

Interesting Bill. I'd never thought about that. It would be good to get boB from Midnite or someone else with experience designing these type of inverters to weigh in on what they do to meet the UL 1741 anti-islanding requirement.

I don't now how my Outback inverter handles it but I do know that even with the Sell RE feature turned off -the idle draw is less than 1 amp on my 48V system. I am in the process of designing a setting up a higher resolution system for measuring both AC and DC currents in my ePanel - to and from inverter, CC and battery bank. The way the GVFX monitors current in and out now has very poor resolution - on the order of +/- 1 amp.

One I get that in place it will be easy tease out whether the Outback's own current draw while under load changes when the "Sell RE" feature is turned off.

BB.

Re: MPPT's working

Just to be clear--The 100-200 watt load is on the AC grid input--I am not talking about and DC "idling" losses.

People, to get around the utility regulations against GT Inverter and selling to the grid is to get some sort of solar power system that still can cost effectively make power for local use and not "accidentally" sell back to the grid (see--Mr. Utility Man, not Grid Tied/Utility Interactive, so you cannot ding me for having solar powered AC circuits.).

However, technically, it is even illegal in California to install a completely off grid solar power system in your home and start moving loads from the grid to the off grid system.

Again, the theory is that the "utility owns your loads" and took out loans/made investments that "you" are legally going to be their customer over the next 20-40 years. And if "you" leave the utility (cut off power) or generate your power locally (solar, generator, etc.)--You have violated the PUC (public utility commission) regulations that were put in place to "protect you" and the utility.

-Bill

inetdog

Re: MPPT's working

BB. wrote: »

Again, the theory is that the "utility owns your loads" and took out loans/made investments that "you" are legally going to be their customer over the next 20-40 years. And if "you" leave the utility (cut off power) or generate your power locally (solar, generator, etc.)--You have violated the PUC (public utility commission) regulations that were put in place to "protect you" and the utility.

-Bill

Next step will be requiring you to pre-pay your estimated electric bill for 20 years before you can get a permit to tear down a house. :-)

BB.

Re: MPPT's working

That gets into the whole question--If you stop paying your bill and the utility cuts your power--Do you still need to pay the stranding charges?

-Bill "the sound of one hand clapping" B.

mtdoc

Re: MPPT's working

BB. wrote: »

Just to be clear--The 100-200 watt load is on the AC grid input--I am not talking about and DC "idling" losses.

Right , idle power is not the best term. Of course for a hybrid type inverter there is no direct connection between PV and inverter and I don't think the inverter derives any power directly from the AC input - though I could be wrong. At least with my inverter it will not even turn on unless it it connected to a battery bank.

I guess the question is when connected to the grid but with Selling turned off - does the inverter consume more power to ensure there is no unintentional backfeeding to the grid. If it does consume more, where does that power come from? At least for my inverter if there is any extra power required I don't think it comes from the AC input because even with Sell RE turned off, if there are no loads on the system there is no measured AC input current (at least as displayed by the Mate - I should measure it directly with a meter..).

NorthGuy

Re: MPPT's working

mtdoc wrote: »

I guess the question is when connected to the grid but with Selling turned off - does the inverter consume more power to ensure there is no unintentional backfeeding to the grid. If it does consume more, where does that power come from? At least for my inverter if there is any extra power required I don't think it comes from the AC input because even with Sell RE turned off, if there are no loads on the system there is no measured AC input current (at least as displayed by the Mate - I should measure it directly with a meter..).

For Xantrex XW: It does not consume more power when selling is turned off. It produces less power than is needed to run the loads. As a result, loads draw some small amout (~1A) from tha AC input (grid).