Just like the leaves on the trees, your home’s energy production changes with the seasons. In fact, certain weather conditions can have a noticeable effect on your system, decreasing efficiency by as much as 25 percent.

But with the right equipment, you can keep your panels humming away all year long. Here’s what you need to know about seasonal fluctuations—and what you can do to adjust for them.

Autumn landscape with solar panels

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Hot Weather May Limit Solar Potential

Even though a sunny day seems like the perfect weather for generating solar energy, solar cells are actually more efficient when the temperature is lower. Solar energy is generated from light, not heat, so while your panels appreciate all the summer sunshine, they may not be as amenable to the heat. To understand why, you have to know a little bit about how the energy in your solar cells is created, so strap on your science hats and bear with us for a minute.

Solar panels generate electricity by harvesting the energy created when ions go from a low energy state to a high energy state, as they do when the sun shines down on them. So, when the materials inside your solar cells are in a low energy state—like they are when it’s reasonably chilly outside—the sun striking them has a much bigger effect than it does on panels that are already warm. Fluctuations in temperature can affect your panels’ performance, even by as much as 10 to 25 percent in some cases.

But not every panel reacts the same to hot weather. To gauge your equipment’s individual performance, review the temperature coefficient, which should be listed among the manufacturer’s specifications. This number will usually be expressed as a negative percentage, which indicates the amount that production drops when the temperatures rise above around 77 degrees Fahrenheit. For instance, if you purchase panels with a -0.48% temperature coefficient, the maximum power output will go down 0.48 percent on days over 77 degrees.

In general, though, thin film solar modules outperform crystalline silicon panels for hot weather efficiency. Of the thin film materials available, cells made with amorphous silicon (often shortened to a-Si) shows the greatest potential for hot climate installations. In some tests, a-Si modules had a power reduction of only 2 percent at temperatures above 100 degrees Fahrenheit, which is much less than your average crystalline silicon panel. If you live in a region where the weather regularly climbs above 77 degrees Fahrenheit, consult with your panel salesperson to make sure you’re buying the most efficient cells for your home.

Snow-Covered Panels Can Cause Brief Drops in Energy Generation

Yes, panels will perform better in cooler temperatures, but they’re not big fans of snow storms, either. Snow sitting on the surface of your panels obviously limits production, since the cells can’t absorb the sunlight under these conditions. But if you live in a snowy climate, the orientation of your panels can make all the difference.

In general, a horizontally-oriented mount will prevent snow from gathering at the edge of the panels, which can cause freezing and other problems during particularly harsh weather. And some research has shown that a mount featuring landscape-oriented panels with vertical racks are beneficial for cold-climate homes, since they gather less snow beneath the panels.

Row of huge solar panels producing electricity

The Sun’s Angle Affects Panel Productivity

If you’ve done some research about solar panels, you may already know that a home’s latitude and the tilt of its solar panels can affect energy production. However, the angle of the sunlight changes throughout the year as the seasons progress, which is why you might get more energy one part of the year than another.

During the summer, that light is more direct than in the winter—at least in the Northern hemisphere. For this reason, you’ll get the best performance if you adjust the tilt of your panels twice a year.

  • In the summer, position them at a low angle, since the sun sits more directly overhead at this time of year.
  • In the winter, angle them higher to catch the maximum amount of winter light.

As a general rule of thumb, most experts recommend setting the angle at 15 degrees higher in the winter, and 15 degrees lower in the summer. If you really want to squeeze everything you can out of that sunlight, though, you can purchase an automatic tracking system that will do the work for you. These systems can generate up to 25 percent more energy in ideal conditions, but they do cost more than a fixed angle module.

Of course, your solar representative is your best resource for making these decisions. They can help you make the most educated choice by factoring for your rooftop’s specific conditions. But if you want to get started now, this solar calculator will give you some idea of how much energy your panels will generate all year—and what you’ll need to spend to get there. The weather may be unpredictable, but your finances will be on lock!