Solar system performance issues???

[noahbraget]

I have been working on my own off grid system the past few months and am new to solar. My system consists of 2 SunGoldPower TP6048 6KW Inverter/chargers in parallel (which have been a nightmare, but that is for a different post) and 48 used Solarworld SW245 Mono panels. The panels are connected 12s2p to each inverter to be at the max inverter input voltage of 450v and just under the power max at 5,880 watts (at full performance). Since this is still a work in project, I currently have the panels flat on the ground and I live in North Texas.

The thing I am questioning in the performance of the inverter and panels. When I tested the panels, they were all around the specified Voc at 36-37vdc. The current for each was measuring around 6 amps. When I measured one series string, it was around 430vdc and the current was still around the 6 amps. Once I connected it to my inverter however, the voltage remained the same but the current dropped down to around half the measured current when disconnected. Is this normal?

Because of this, my roughly 12kw of panels have produced 6kw at the peak (which may have been in October when I first set the system up.

I'm trying to figure out if my junk inverters have yet another problem since they won't accept the full amperage the panels put out, or if this should be expected until I get the panels mounted on rails at the proper angle.

Thanks!

 

[PreppenWolf]

What is your wiring situation from the panels to Inverter? What length, type and gauge of wire?

 

[sunshine_eggo]

If this unit has a Voc limit of 450VDC, I would be concerned that your 12S array is too close to the 450V limit. I don't know if that would affect performance, but you don't want to pop the MPPT.

Flat panels in northern hemisphere during winter are lucky to produce 40-50% rated. 6kW vs. 12kW rated sounds good to me. It's just a few days past winter solstice, so the sun is about 55-60° off of perpendicular assuming you're around 30-35°N latitude.

 

[Hedges]

Series string 430Voc sounds correct.
Did you actually measure Isc, 6A, for the series string? Curious what you used to connect/disconnect ammeter in a 430V DC circuit.

SolarWorld SW 245 Mono Solar Panel

Buy SolarWorld SW 245 Mono solar panels for home or commercial solar systems. SolarWorld SW 245 panel sales, reviews and low wholesale prices.

www.solarelectricsupply.com

"

Open Circuit Voltage (V)	37.5
Short Circuit Current (A)	8.49

"

https://d140hlzzaoq16w.cloudfront.net/media/sparsh/product_attachment/custom/upload/solarworld-sw-245-mono.pdf

"Maximum power Pmax Open circuit voltage Voc Maximum power point voltage V mpp Short-circuit current Isc Maximum power point current Impp SW 245 245 Wp 37.7 V 30.8 V 8.25 A 7.96 A"

Voltage as expected. Panels flat on ground, off-season, 6A Isc is not unreasonable. With one panel you could try tilting directly at sun, see what you get.

"Once I connected it to my inverter however, the voltage remained the same but the current dropped down to around half the measured current when disconnected. Is this normal?"

Half the current, 3A? Connected to inverter, or disconnected?

If open circuit, expect same voltage. If disconnected and tested under short circuit conditions, expect same current as before.
Operating with inverter and MPPT, expect voltage around Vmp or 30V (80% of Voc) and current about 95% of Isc.

But if battery nearly charged and no loads, inverter will draw less current and voltage will be higher.


12kW (STC) of panels producing 6kW off-season at with wrong angle is not unexpected. Under nominal conditions, most panels are rated to produce 75% or 85% of STC. Some cold days with sun high in the sky you may get 100%.

The ad I linked says,

"

STC Rating	245.0
PTC Rating	219.6

"

So expected output of 220W under nominal conditions is pretty close to 245W lab conditions (one standard sun, panel at 25 degrees C.)

Put a load on your inverter, 9kW to 12kW if using all panels or 2 to 3kW with just one string, see how it performs.

How about a link to your inverter?! This one I found:

6000W 48V Hybrid Solar Inverter Split Phase 120/240VAC (Grid Feedback & Batteryless)

Hightlight: ★ Solar Inverter Charger: 6000W DC 48V Split Phase Low Frequency Inverter, AC input 240V AC, AC Output 120V/240V, MPPT Max 120A solar charger and 120A AC charger 100A ★ Parallel Kit: This grid tie solar inverter parallel supports up to 9 units (54KW Max), 120V/240V split phase output...

sungoldpower.com

says 120 to 430V MPPT operation, 450V maximum.

You may be in danger of killing it in cold weather, when voltage from PV panels rises as much as 15%.

 

[PreppenWolf]

If you are near Amarillo, your best angle is far from horizontal with south facing panels.

 

[PreppenWolf]

Prop the panels up at 45deg and see what you get.

I also second looking at lowering your input voltage. I have a 500V max and I keep mine below 450V. Yoy need more headroom IMO than risking 430V full time. You're one very cold day from possible lights out.

The next question I have is what are you putting the energy into? If you don't have a load (whether using power or se ding it to batt storage) the unit will just "turn down" the intake.

 

[noahbraget]

@PreppenWolf I am using 10 AWG stranded THHN wire. The positive line is about 30' and the negative is about 100' from the combiner box/inverter. I am north of Dallas and it looks like optimal all year angle is 28.6 degrees which I will do when I mount.

I do plan on switching to 11s (and did that over this last weekend) since I did go slightly over at 458v. My inverter gave an over voltage warning but returned to normal after I switched to 11s.

I have a roughly 24kw lifepo4 battery bank that it goes to in addition to the load. I have my max charge rate for both the inverter and BMS set at 120 amps.

@sunshine_eggo I appreciate that info. I know that they do have lower performance, but I was unsure of what that extent was. The only part I was curious about was that the amps were different when connected only to my multimeter vs connected to the inverter.

@Hedges The 6 amp measurement was for the series. And when I connected the panels to the inverter with the inverter on, my clamp meter read around the 3 amps which was in line with the calculated value based on the voltage and watt reading on the inverter. These measurements were with my batteries nearly empty and I did have a load on (heat pump).

That is the inverter I have. As mentioned above, I did recently switch to 11s to give more breathing room.

If y'all think it is normal for the panels to drop in current once connected to the inverter/charger, I will chalk that up to normal. What my current belief is that the inverters which have had numerous problems from day 1 are somehow throttling the input from the solar which is causing the lower amp draw. I do plan on replacing the couple month old inverters as soon as I can with something much more reliable.

 

[PreppenWolf]

No linky to your inverter above.

 

[Hedges]

I expect Imp to be fairly close to Isc, but voltage to drop more (like 20% drop.)
If you measure 6A short circuit but only 3A MPPT with loads, something doesn't seem right.
My first thought was if PV voltage was too low, MPPT couldn't draw enough current at minimum operating voltage. But that doesn't seem to be the case.

Some PV panels, usually the half-cell ones, are wired internally as 2p. Shade on half can drop current in half. Testing Isc, voltage is pulled low enough that bypass diode is activated so you see full current (6A) of the other panels, but an MPPT that doesn't explore entire voltage range can stop at higher voltage local maxima of power, and get only 3A.

But your panels are single cell. Could still happen if one puts out partial current for some reason, either shade or damage. Are these new panels, or used? I had some panels go bad, tracked it down once I tested them individually with resistive load. Performance of array was restored when I replaced the bad panels.

Measuring PV panel performance

I suppose I could buy a solar panel tester like Will reviewed, but that doesn't feel DIY enough to me. Besides, I'm a cheapskate, and I try to do things in the most difficult (and expensive if the equipment wasn't on hand) way. I'm presently working on an underperforming string of Sharp 165W...

diysolarforum.com

Segment your array into eight 6s strings. Test inverter operation with each individually. If some underperform the others, find a way to narrow down, maybe swapping one panel at a time into a well performing string.