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Solar layout - Does this need optimizers?

bevo

Member
Mar 10, 2021
39
16
Irvine
If enough panels on a string are shaded you will have no output from that string if the total string voltage is below the inverter minimum. So you may want to consider that when figuring out how to run your strings. 8 strings for 48 panels seems like a bad idea because on a 6 panel you may only need to lose one panel to have the whole string drop out.
SolarEdge 7.6kW inverter supports 2 strings. Tesla 7.6kW inverter supports 4 strings. Perhaps Tesla doubled the strings and cut the operating voltage in half? Probably not but it's hard to say since they didn't publish this spec so it can't really be determined the minimum number of panels needed per string. Unless this spec is published and I'm just not seeing it?
 

nwdiver

Well-Known Member
Feb 17, 2013
7,743
9,958
United States
SolarEdge 7.6kW inverter supports 2 strings. Tesla 7.6kW inverter supports 4 strings. Perhaps Tesla doubled the strings and cut the operating voltage in half? Probably not but it's hard to say since they didn't publish this spec so it can't really be determined the minimum number of panels needed per string. Unless this spec is published and I'm just not seeing it?

Here are some design notes that were posted on a previous thread. They're for the solar roof but should apply to any solar design. The 4 channels are for flexibility. I would expect most installs to only use 3 channels to maintain longer strings. Generally speaking longer strings and higher voltages are better.

 

rxlawdude

Active Member
Jul 10, 2015
2,356
1,626
Orange County, CA
Nope. If one panel is completely shaded and all other are in clear sunlight, a string inverter will output nominally the same power as an optimizer or microinverter system.

And each MPP channel should preferably have 10-13 panels to keep within the MPP range of the inverter, both on bright days (13 panels to avoid overvoltage) and on overcast days or at times noticeably different than solar noon (~10 panels). So in the OP's situation, it is probably best (if using a string inverter) to have 11, 12, 12, and 13 panels on 4 strings. Even better would be to add 2 panels in the open spots, if that is cheaper than going with a non-Tesla installer and an optimizer/microinverter setup.

Optimizers can help. To take a simple example for the OP's setup, if the chimney is casting a shadow anywhere on the bottom half of a single panel, then a string optimizer will probably get zero power from that panel (and full power from the others). But these are half cell panels, which means the upper half is capable of generating half the current that a fully illuminated panel can. An optimizer setup can use that upper half's output, or up to 170 watts more total output than a string setup. It is difficult to justify this increased power financially, however.

As already suggested, putting 12 unshaded panels on the east side will give just as much power as 12 unshaded panels on the west side. The maximum output will occur in the morning instead of afternoon, if that is an issue.
Thanks for educating me! My understanding was based on our installation back in 2015.
 
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Mar 1, 2021
118
32
San Diego, CA
If enough panels on a string are shaded you will have no output from that string if the total string voltage is below the inverter minimum. So you may want to consider that when figuring out how to run your strings. 8 strings for 48 panels seems like a bad idea because on a 6 panel you may only need to lose one panel to have the whole string drop out.
Modern inverters have very low minimum input voltages, the delta M8 for my install works down to 50V.
 
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nwdiver

Well-Known Member
Feb 17, 2013
7,743
9,958
United States
My Solaredge inverter requires at least 350 volts so I guess that's an advantage of the Delta. I need at least 6 panels clear on a string to make any power.

Solaredge is a bit different. The inverter requires 350v but the optimizers can boost their voltage to 60v to get to 350 and even fully shaded panels can help boost voltage. So you can get to 350v with only 6 panels. IIRC the minimum string length is 9. Traditional string inverters need a wide voltage range because they perform MPPT. With a SE system the MPPT function is performed by the optimizers not the inverter.
 
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arnolddeleon

Supporting Member
Jul 21, 2012
745
829
SF Bay Area
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