The fourth choice will actually determine what type of solar panel plans will actually work. As it turns out, the popular solar panels are polycrystalline. And this cell technology has a negative output voltage vs. temperature coefficient. Another way to state that is that the voltage gets higher as the temperature gets lower.
Believe it or not this is a very critical design parameter. Systems that are designed for use in Florida can self destruct when they are installed in Michigan because the Florida design would probably assume the lowest operating temperature of around 25 degrees. Here in Michigan sometimes get sunny days with below zero temperatures. This difference can raise the output voltage enough that the rest of the system is at risk of failing.
So in our case we needed to do some research to find the historic low temperatures and make some assumptions about low temperatures when sunlight would be hitting the panels. The record low temperature going back eighteen years waas -22 degrees F. And that would have been at night when the solar panels wouldn’t be generating any voltage. We chose to design our system based on a lowest possible temperature of -14 degrees F.
This design choice is particularly interesting when you realize that two of the system quotes we received were actually improperly designed for Michigan installations. I spoke to another engineer-homeowner who installed solar panels in 2010 and he also received proposals that had this same design error. So, be careful with this!
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