Hi all,
I've been reading up about solar, and one thing confuses me (well lots of things do, but you have to start somewhere!)
From what I have read, if you have a string of identical panels in series and one of the panels becomes shaded, the power output of the whole string drops to match the shaded panel.
Obviously this is confusing, because it is a total and utter made up lie. It does not work that way. For example, I have a string of 10 panels where I get 1 to 2 completely shaded panels in late afternoon. No such effect.
Sometimes it is just people who have no idea what they are talking about trying to be "helpful" but actually doing harm. Sometimes it's a microinverter or "optimizer" FUD BS market guy.
I'm surprised such bullcrap is seen in this thread, too:
This happens
No it won't, so the rest of the post is BS too.
How can people be so oblivious to such commonplace urban myth so that they keep writing responses happily assuming it was true, instead of shooting it down as the very first thing?
In reality, shaded panel cannot produce the same current, that much is true. This causes the voltage to change, look at the U-I curve set of the panel. The voltage tries to go
negative, and current starts flowing through the bypass diodes installed in the junction box.
As a result, shaded panel production goes to zero, but rest of the panels keep producing optimally, assuming non-broken MPPT algorithm.
Actual panels usually consist of 3 "sub-panels" (with 3 bypass diodes, too), so that if you partially shade 1/3rd of the panel, only that part goes to zero, and rest of the panel keeps optimal production.
This is also why microinverters and "optimizers" rarely make economic sense: if you have say 10 * 300W panels, each producing 300W for 3000W total, and you partially shade one of them to production potential of 30W, in a microinverter system you could have 9*300W + 1*30W, and with string inverter you could have 9*300W + 1*0W. It is simple as that. However, string inverters tend to have a few %-point better efficiency than micros, this evens out the difference in typical installation where there is only very minor shading. Microinverters are recommendable when there is a lot of shading, sometimes half of the panels, or the panels are not in the same plane but point in whatever directions.