will get back with more info in a couple of days. something always comes up.
solar problems/need guidance
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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?Comment
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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?
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.Comment
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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.
CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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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.
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.Comment
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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.
CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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Originally posted by max2kNew transformerless inverters should be then even better in this regard as they are constantly switching strings around ground potential.Comment
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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 RoeComment
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Also, for what it is worth, the problem is with *accumulation*. If the string is negative grounded, the high voltage end will degrade faster, but ultimately, they would all degrade. (See Figure 6 in the paper, showing the same degradation after 100 min of +1000 V, but after 1000 min of +100 V)Last edited by sensij; 10-12-2017, 07:41 PM.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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will this inverter work with a positive ground?Attached FilesComment
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You are using Sunpower panels? Which model? The positive grounding was only required for the designs Sunpower (and only Sunpower) produced 10 years ago or so.
Also, for what it is worth, the problem is with *accumulation*. If the string is negative grounded, the high voltage end will degrade faster, but ultimately, they would all degrade. (See Figure 6 in the paper, showing the same degradation after 100 min of +1000 V, but after 1000 min of +100 V)
made for a decade, I can see why. Bruce RoeComment
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