Most people will agree that the record hot spell this summer has been unbearable, but it’s equally taxing on solar panels. You would think hot temperatures equal a lot of sunny weather and this would be great for solar panels. Sun is a photovoltaic panel’s best friend; however, high temperatures can be their worst enemy.

The world is getting hotter.

Record breaking heat and long periods of thick humidity have been assaulting New Englanders and making it pretty miserable for residents of Massachusetts. The National Weather Service says there were 10 days with temperatures over 90 degrees or more in Boston. The record for the month was 15 days, set in 1994. The weather service also said average daily temperatures for Boston and Hartford in July were about 4 degrees above average.

So what do higher temperatures do to solar panels?

As temperatures rise, the efficiency of solar panels decreases. Heat causes electrical resistance to the flow of electrons. On days where the temperature is more than 75 degrees, the electrical resistance makes the voltage fall thereby producing less kilowatts per hour. Your roof is much hotter than temperatures on the ground. That’s why solar panels are not mounted flat to a roof. There’s usually a few inches of spaces between the panels and roof so air flow can easily pass through and cool the panels down.

Some solar panels are designed to operate in hotter temperatures.

These panels have a higher temperature coefficient. This is especially important in high heat climates like Arizona or New Mexico, but probably wouldn’t make too much of a difference in New England (except maybe this year). If you do live in one of these areas, you should speak to your solar installer to make sure they are using they right equipment for your region.

Please note: Solar thermal panels used to heat water can withstand high temperatures without any degradation. In fact, hotter temperatures would actually be better for these types of modules.