Anyone looking to lower their energy costs by switching to clean and renewable solar power will want to know two numbers.
The cost of installation.
The amount of solar energy that will be produced.
Fortunately, any reputable solar installer ought to be able to provide an estimate of both.
But while the price tag is pretty straightforward, estimating how much solar power you're going to get is a bit tricky. And some of the complexities have the potential to cause confusion.
Production estimates
Electricity consumption is measured in kilowatt-hours (kWh).
So, any production estimate you get from an installer will specify how many kWh of solar energy you can expect your panels to generate each year given local weather conditions.
Suppose, for example, that you get a production estimate for a proposed solar system saying it will generate 900 kWh of solar energy annually and that happens to be the exact amount of electricity you consume.
Since your panels ought to be producing all the electricity you need, it's natural to expect that you'll never have to be billed for electricity again.
Monthly production varies with the sun
But the fact that your panels will generate 900 kWh of energy each year does not mean that they're going to produce 900 ÷ 12 or 75 kWh every month.
Because solar power is derived from sunlight, the amount of energy your panels produce will vary from month to month depending on how sunny it is.
So, a production estimate that says you're going to get 900 kWh of solar energy annually doesn't imply you'll be getting 75 kWh each month. In the summer, you'll be getting more solar energy than that, but in the winter months, you'll be getting less.
The exact percentages will vary depending on your location, the direction your panels face, the angle at which they sit, and the existence of any trees or other objects that might obstruct sunlight.
But, on average, you can expect your solar panels to generate around twice as much energy during the spring and summer as they do during the fall and winter.
Breaking it down
To get an idea of how much of your total solar power production estimate you can expect each month, here's a monthly breakdown of the energy output from an enormous solar panel farm in the northeastern U.S.
As you can see, the amount of solar energy generated increases as it gets closer to summer, resulting in July's production peaking at over three times higher than December's low.
Why there's less solar energy in winter
Three factors are primarily responsible for the discrepancy between summer and winter solar power production.
Shorter winter days mean that your panels will be getting fewer daily hours of sunlight.
The sun also shines down less directly in winter months. Even at its mid-day peak, the sun is much lower in the sky in December than it is in June. That means less direct sunlight and, hence, less solar energy.
Finally, the winter also brings more clouds, further obstructing the season's already diminished supply of sunlight.
What to expect
The upshot is that your panels are going to be producing significantly less solar energy in the winter than they do in the summer.
So, if your solar system was installed in the winter, don't be surprised if it initially winds up generating less energy each month than the average monthly production estimate you were given.
Come springtime, the amount of solar energy you're getting will increase and start exceeding your monthly average production estimate. And that summertime surplus ought to balance out the winter deficit.
In short, even after your solar system is installed, you should expect higher electric bills in the winter and lower ones in the summer. But once the entire year is taken into account, the amount of solar energy your panels produce ought to be pretty close to the initial production estimate you were given.