question

Thanks. I see the Temperature Coefficient in the table now. So, just to see if I actually more or less understand, I'll work things through for an extreme case (using info on the two-page specifications sheet)...

Assume (for example) the panels are perfectly aligned and operating at local "noon" (maximum solar irradiance) one day. The Normal Operating Temp of the cells would be about 41 C (spec. sheet). The next day, same time, it's been totally overcast and cold so the cells have been "off" (non-irradiated) and could be at 15 C = 59 F. Suddenly the clouds clear and the cells start up under full irradiance while cold with no load (batteries charged, everything beyond the inverter turned off because we are out of town, inverter itself drawing negligible power for control circuits, so open circuit conditions). The voltage per panel could easily be somewhere between (48.7 and 49.7 v) * (1 - (0.0026 v/C)*(15 C - 25 C) = (49.97v to 50.99v). Under these conditions with three panels, even the [??lowest peak irradiance induced output power range??] (395W column) Voc is at the open circuit limit of the charge controller. The higher power range values (up to 420W) are beyond the limit (3 x 51v = 153 v > 150v). Without knowing the local irradiance, this (15 C startup) is about the first temperature where all of the listed performance scenarios have Voc at or above the charge controller limit. Presumably, the starting temperature could hypothetically (and perhaps over simplistically) be about 1.5 times colder (in extreme conditions that have happened here in the distant past, maybe down to 0 C). So there could possibly be conditions where any level of peak local solar irradiance (the columns in the spec table) would be enough to produce too much Voc for the charge controller with 3 panels in series. So, 2 panels in series it is.

I of course don't know what is realistic for the time response for T and V of the cells, so I don't know how over conservative (or not) the above is, but at least it is safe. Is the above more or less the train of reasoning one needs to go through?

Thanks again,

Robert

p.s. For Trina Solar: It would be nice for us customers if you could list in the specs table the normal irradiance that produces each of the listed Peak Powers (existing column headings) so we could know which of the columns in the table we are supposed to use. As is, I have to have a panel already in place and working so that I can look at a historical record of Power Output (V, I) in order to know which column of the specifications table to use. You've already gone to a lot of trouble with your spec. sheet. Just dot an "i" and cross a "t" and it would be perfect. Thanks. R. C. Blasdell, Ph.D. (physics)