Panels fading on hot days
I have 2 strings of 4 x 410 W Canadian Solar panels each, one facing East and the other West. The roof forced this layout. It works very well, except for days over 30 C without wind. BTW this is in Boston Estate, Bellville, Cape Town. One of the original reasons for buying here is that this suburb is protected against the worst of the Southeaster, when the wind howls just 5 km from here, we would have a moderate breeze. On low/no wind days, the string output drops to 50W even in bright sunshine. I have hosed them down in this state and the effect is dramatic; the power shoots up to 1 kW+, only to slowly degrade to 50 again. After getting the installers back for a check of the whole system, they declared everything good, but also said they don't know why this happens, haven't seen it before in all their many installations.
My son came up with an idea that I want to put up for discussion here: The two strings deliver voltages around 130 V. This could be at the low end for the 5 kW inverter, but it can cope under normal conditions. Once the panels heat up above a certain threshold, there may be a voltage drop causing the inverter to back off. It sounds like a plausible theory, but when I looked at the voltage traces during these periods, they looked very normal. Maybe the effect is too small to see on the graph?
Any bright ideas?
Thx
Oubaas Pretorius
That won't work properly. In the morning one string will be fully bypassed with the diodes, in the evening the other, you will get decent generation around midday when both panels have equal amount of sun.