solar problems/need guidance

[bcroe]

Those panels really require an inverter that will make sure they operate at
negative voltage (positive grounding). Here is a paper *** explaining what is going on.

TL;dr - If the panel voltage is above ground potential, 203 W output would (reversibly) degrade to 140 W.

If that were a notable effect in the field, I would expect to see the panels near the positive
end of a high voltage string put out 5% less power than those near the ground end. No
such effect has been observed here, or seen reported. My inverters are neg gnd. Bruce Roe

[bcroe]

New transformerless inverters should be then even better in this regard as they are constantly switching strings around ground potential.

Could you please elaborate on "switching strings around ground potential"? thanks, Bruce Roe

[sensij]

how those panels worked in the OP strings to begin with as being connected in series inevitably puts panels at the ever increasing potential to the ground towards the end of the strings?

No. If you put a panel at -40 V in series with another panel at -40 V, you get -80 volts. That is what positive grounding does. The OP's strings, as installed with those SPR3200 inverters, were entirely below ground potential, avoiding the effect described in the paper.

Sunpower *did* in fact eventually change the construction of their panels, so that positive grounding was no longer required. The thrust of the paper was not that Sunpower panels outperform, but that the reason they *underperformed* with conventional negative grounding was because of charge accumulation. By applying -1000 V, the accumulated charge was eliminated and the panels restored back to expected output.

Newer transformerless inverters will not keep the entire array below ground potential, and therefore increase the risk that the OP's panels will suffer from the degradation described.

[max2k]

Those panels really require an inverter that will make sure they operate at negative voltage (positive grounding). Here is a paper explaining what is going on.

TL;dr - If the panel voltage is above ground potential, 203 W output would (reversibly) degrade to 140 W.

I don't know how those panels would perform with a transformerless inverter, but I doubt it will work well.

The SBxxxxUS series of inverters are transformer based, and field configurable for positive ground. Renvu still has the 3000 W, 4000 W, and 6000 W models available on their specials page. They don't have AFCI, or ground fault protection on both conductors, so they are difficult to put into a new installation and be compliant with code.

how those panels worked in the OP strings to begin with as being connected in series inevitably puts panels at the ever increasing potential to the ground towards the end of the strings?

the article sounds fishy to me, they might have just washed the panels by providing 'water film' over cells front surface. Sounds all too similar to statement JPM made once that "any research will confirm what the client pays for" or something to that point. At the end they also state that SP is going to put conductive layer on the cells themselves (under the glass I presume) to mitigate this effect so from the outside their panels would have the same interface anyway.

New transformerless inverters should be then even better in this regard as they are constantly switching strings around ground potential. I wouldn't let SP semi- marketing article drive my decision as their panels were not performing any better than of any other reputable manufacturer based on multiple member's posts here.

[sensij]

Those panels really require an inverter that will make sure they operate at negative voltage (positive grounding). Here is a paper explaining what is going on.

TL;dr - If the panel voltage is above ground potential, 203 W output would (reversibly) degrade to 140 W.

I don't know how those panels would perform with a transformerless inverter, but I doubt it will work well.

The SBxxxxUS series of inverters are transformer based, and field configurable for positive ground. Renvu still has the 3000 W, 4000 W, and 6000 W models available on their specials page. They don't have AFCI, or ground fault protection on both conductors, so they are difficult to put into a new installation and be compliant with code.

[tim a]

this is the layout

[tim a]

all face same directions, no shade

[max2k]

its been a long couple of days but here is the latest info. turns out all 3 inverters are bad. so now I need to replace them. what I have is 46 panels of sunpower panels. each one is 210w 5 amp 40 v.
they are wired -- 8 panels in series and 2 strings ties together. except the last string has only 7 panels. so being a positive ground what would be the best replacement inverters? I can change the strings around if needed. I seen the sma sunyboy inverters. maybe 2 5000, or can I just change to 1 inverter? any suggestions?

Do they all face the same direction and do you have any shading? SMA SB as well as many other modern inverters expect ungrounded panels meaning neither '+' nor '-' DC is connected to the ground but the frames, etc are of course connected.

SMA SB have max input voltage of 600V which allows for longer strings (up to 12/string). 210W x 46 = 9,660 rated power. If you can live with some clipping single SB 7.7 inverter clips at 7,950W. It has 3 independent MPPT inputs 10A each. You can connect your 46 panels in 4 strings and connect them as: 12 + 12 + 11||11 panel strings to its 3 inputs. 2x 11-panel strings will be connected in parallel. If your panels face different directions this would complicate things as while inverter can support up to 3 directions we need to know how many panels are in each direction as only those in the same direction could be connected in the same string.

[tim a]

its been a long couple of days but here is the latest info. turns out all 3 inverters are bad. so now I need to replace them. what I have is 46 panels of sunpower panels. each one is 210w 5 amp 40 v.
they are wired -- 8 panels in series and 2 strings ties together. except the last string has only 7 panels. so being a positive ground what would be the best replacement inverters? I can change the strings around if needed. I seen the sma sunyboy inverters. maybe 2 5000, or can I just change to 1 inverter? any suggestions?

[tim a]

will get back with more info in a couple of days. something always comes up.

[sensij]

So, it sounds like the string is at heathy voltage, but the inverter isn't getting past its self test and actually making power. The -84 W on the inverter display doesn't sound good... As though it is drawing power from the grid, not generating it. All three doing the same thing is kind of weird... Could 84 be an error code? I'm not someplace I can look at the manual easily.

[max2k]

thanks foe the response. the reason I asked the question is the inverters have 250- 340 depending on the sun but with a clamp meter I am getting a very low amp reading., .04 amps and on each inverter panel it is reading( approx. - 84 watts.) the the electric meter still is going forward. this never changes always negative watts and meter always runs forward. even during the hottest time of day.

your clamp meter reading seems to be x7 times off: 84W / 300V = 0.28A, this is way too much for normal measurement error.

Can you provide more details how/where did you put it and post some pic/model # of the meter? Could you also clarify what did you mean by 'always negative watts'?

[tim a]

thanks foe the response. the reason I asked the question is the inverters have 250- 340 depending on the sun but with a clamp meter I am getting a very low amp reading., .04 amps and on each inverter panel it is reading( approx. - 84 watts.) the the electric meter still is going forward. this never changes always negative watts and meter always runs forward. even during the hottest time of day.

[Mike90250]

can the solar panels have the correct voltage and produce none or little amps?

Yes, at early dawn hours, even a little bit of light produces nearly full voltage, but the Amount of light produces the Amps. So pre-dawn, when cold, panels produce their highest voltage (Voc) before the controller can awake and make use of the the power.

If that morning voltage is higher than the controller spec, the high voltage (lo amps) fries the controller. That's why most controllers have a Panel String Calculator to determine the max # of panels in a string

[max2k]

can the solar panels have the correct voltage and produce none or little amps?

if there's not much sunlight falling on it- sure.