Updated: Feb 28, 2021
The sun is pretty strong here in Texas, where summer heat between 90°F and 110°F mostly overextends to spring and fall every year in some parts of the state. You would think that is the ideal situation for solar panels—a logical thought process that solar heat equals good solar production.
Well, in reality, the impact hot weather has on solar panels can be quite the opposite of what most people think—I explain.
It's true that shade, cloudy days and absence of sunlight will diminish or completely wipe out solar production, but so will too much sun heat. Wait... say what?
Most people don't know this and much less wouldn't even think about it, but the laws of thermodynamics that apply to any electronic equipment also apply to solar panels in that increased heat will decrease it's power output.
Without getting overly technical, solar panel temperatures will generally range between 59°F (15 °C) and 95°F (35 °C) during which solar cells will produce at maximum efficiency. Residential solar panel materials are tested at 77°F (25°C) and their peak power output (PPO) starts to decrease the hotter it gets after that.
So does that mean that on a sunny 77°F day your panels will perform at their rated capacity? Not quite...
The reasoning that your car gets much hotter than the cool 77 degree outside air while sitting out on a parking lot, also applies to your solar panels baking on your roof on a cool sunny day. Therefore, warmer weather conditions will always reflect on decreasing power output for solar cells, and this loss is measured by the manufacturer's “temperature coefficient” , which can also vary from model to model.
Determining Temperature Coefficient
The photovoltaic (PV) temperature coefficient of power indicates the efficiency of the PV array's PPO depended upon the cell temperature—meaning the surface temperature of the PV array, (not the outside air temperature). It is a negative number because power output decreases with increasing cell temperature.
If we take for example the average market temperature coefficient of -0.38% per 33.8 degrees Fahrenheit (1°C), this means that for every 33.8°F above 77°F, the maximum efficiency of a solar panel will decrease by 0.38%. Inversely, for every 33.8°F below 77°F, the maximum efficiency of that solar panel will increase by 0.38%.
So, if the outside temperature were 96°F (or 35.5°C) — the average daily high in Central Texas in the summer—the surface of your solar panels in direct sunlight could roughly increase to 192°F (88.88°C), solar panel efficiency for that solar panel could decrease by approximately 24%.
0.38% x (88.88°C -25°C) = 0.38% x 63.88°C = 0.242 or 24%
As I mentioned before, an important note to keep in mind about temperature coefficients is that PV operating temperatures lower than 77°F will actually be positive and your solar panels will increase in efficiency. In other words, cooler, sunny weather is better for your solar panels and can help offset any diminished summer heat performance.
Contrary to normal popular assumptions, the best conditions for optimal solar production are cold, sunny days, rather than hot summer weather—which in turn means you don’t necessarily have to live in Texas heat like climate to benefit from solar power. However, this by any means suggests that PV systems will perform under what's quoted during warm weather—all this calculations are taken in consideration on a solar proposal. This only means performance increase in colder weather could also help offset losses that occur during warmer summer months, especially for homeowners living in regions with marked season cycles.
MANOLO BARDEGUEZ - Welcome to my Blog. I hope the articles on this site inspire you and I encourage you to discover the benefits of going solar for yourself by clicking Go Solar. By clicking Join you can also learn how you can join our movement to connect the world to sustainable technologies and get paid handsomely by the fastest growing solar company in America. If you have any questions, you can contact me directly by email at ManoloBard@SunbrightNet.com or call me by clicking the phone icon above.