Summer Solar - The Truth Revealed

Summer’s longer days mean more sun time for our modules. You would think that this means your modules will be able to charge your batteries way more than in the winter right? Nope. Surprisingly it is the other way around, at least for those of us living in Arizona where we see heat on our module surface well above 120º in the summer. Winter is actually when we get the most production from our solar modules.

I know what you’re thinking: this guy is crazy, he has to be wrong! I can explain, I promise.

When the sun is shining brightly upon our solar modules it is doing two things: 1) It’s giving off those much needed rays to charge our systems, and 2) it’s heating up the surface of the modules. Summer heat is not good; modules work the best, or most efficiently, when they can collect the sun’s rays and their surface can stay cool. That means we get our best production when the sun is pointed directly at the modules and the weather is colder. When the modules get hot, they cannot transfer the volts as efficiently. The molecules expand inside the solar crystals causing an increase in resistance. This resistance causes a reduction in performance and ultimately lower voltage to our batteries. That is why we love those perfect days in the spring that give us cool weather and lots of sun! May is one of the best months for solar production in Arizona.

How much can this temperature fluctuation change our production? Would you believe that our panels could collect up to 15% more in the winter and 15% less in the summer than their label-rated production? A 17 volt panel can drop to 14.5 volts in the summer and raise to over 19 volts in the winter.

The question now is what can we do to maximize our harvest from the sun in the very hot days of summer? First, the way your modules are connected to each other is one of the most important things you need to review to make sure you can effectively charge your batteries. The amount of volts that your modules give off needs to be higher than what your batteries can hold so that the power can actually be pushed to the batteries. When calculating this, we need to be sure to use the losses created by the heat. If we just hook up a couple of 17 volt modules in series creating what looks to be a 34 volt circuit and hope to charge a 24 volt system, you are going to be very disappointed in their performance.

Second is to make sure you are using the best charge controller for your system. Being sure that your charge controller can harvest every drop of energy that your array produces and can push as much of that energy to the batteries is also very important.