Cloudy Weather? Wire solar panels in parallel!

I received this Email

From Bidjanga:

Hi Pete,
I’ve experienced an issue this day, when testing my burners ; the sky was cloudy with a small and weka sunlight ; i’ve connected the 400W burner to 4 solar panels of 100W/12V hooked in 2S+2P system ; i noticed the heating element of 6.4 ohms in the burner was hardly getting hot ; same result with the burner having the 3.2 ohms heater ; . I then disconnected all the panels and re-connected them in parallel ; tested them with the 3.2 ohms heater burner ; and the heater got very hot : can you please explain why ?

My Response:


Great that you experimented! Yes, this is exactly what you would expect. The physics is explained pretty clearly in the “Hot Diodes!” paper (accessible on our research website). By hooking the panels in parallel completely, you doubled the power output when the sky is cloudy. You will notice that if you do that when the sun is strong, it will decrease the heating. So, yes, more voltage (in series) when the sun is strong, and more current (in parallel) when the sun is weak… essentially, it’s because the strength of the sunlight increases the current (not the voltage), so if the sun is weak, you have to increase the current by putting them in parallel. We are developing a simple electrical circuit that will do this.

But 4 take-aways:

  1. It’s exactly what we should expect.
  2. It’s discussed at length in the “Hot Diodes” paper.
  3. It’s great that you experimented with it!
  4. We’re designing an inexpensive circuit that should do this automatically.

I hope this helps!


Of course, Pete !
your comments did help me understanding the issue.