What is it you might ask? They don't work in the heat. My system went live Sept 9, 2010. In today's technology age I can check second by second how much electricity it's producing. In Pennsylvania, we've had a remarkable string of sunny, almost cloudless days going back to 3-4 days before memorial day. My thought was my system is racking up the Kilowatts! As I checked my graphs on daily production with the guy who installed the system (and several other commercial systems), I couldn't help but notice that about 3 days of the production was down 20-40%, which I didn't understand. So of course, my installer is sitting by my side. What happened these 3 days I ask? Oh those were the days it was 90-95. Me: So? Installer They don't work so well in the heat! My installer never told me this, and I've read a fair amount about solar panels. Up until 2 weeks ago I never read about it. It was in the local newspaper about a week previously when another local (who built a 1MW system) complained about it. So there you have it folks. They don't shut down, but they are definitely not as efficient in the heat as they are in the cool. Sort of makes the whole 'put them in the desert thing' not such a good idea. Our memorial day weekend temperatures were by far the highest we've had since it went live 9/9. http://www.learnonline.com/pdf/The Effect of Heat on Solar Panel Output.pdf http://www.reuk.co.uk/Effect-of-Temperature-on-Solar-Panels.htm "The total power loss due to the increase in temperature was from around 750 mW down to just 458 mW - a fall of almost 40%! Had the solar panel been pre-cooled in the fridge before the experiment was started the peak power output would certainly have been even higher."