We hear this question a lot: ”I have a 2,300 sq. foot home and like to keep my thermostat around 75 degrees in the summer. How much will solar cost me?”
Don’t get me wrong, this is a perfectly legitimate question. It’s simply not a question we can answer because there are so many more variables needed to get to a final number.
In order to calculate how many panels you will need to purchase, you first need to know the following information: how much energy your family uses monthly and annually, available roof area and orientation, the wattage and efficiency of the panels you are considering, solar rate plans offered by your local power utility, and whether energy buyback programs are available through your utility provider.
This sounds like a lot to the casual reader. The easiest way to answer the “how many solar panels will I need?” question is to consult with a solar integrator, who will give you a free evaluation and quote. But to get your wheels turning, let’s take a closer look at each of these four factors.
1. Your personal energy use: Your utility bills are a gold mine of information. Each bill shows your total energy used on a month-by-month basis, with a comparison to the same month from the previous year. You can even see day-to-day and hour-to-hour consumption. With this data, we can easily calculate how many solar panels you will need by multiplying your hourly energy consumption by the sunlight hours that strike your available roof area, and then dividing that number by a panel’s wattage.
2. Roof area and shading: The amount of roof space available to solar panels, and the amount of sunlight that strikes that area are key to determining energy output. Fortunately, here in the Valley of the Sun, we enjoy more than 300 sunny days every year. So for us, the most important thing is to avoid shading. Trees, adjacent buildings, chimneys, and other structures can all reduce panel output. Our solar integrators do a thorough shade analysis as part of the free quoting process.
3. Panel efficiency: Not all solar panels are created equal. Most commonly used residential panels offer wattages ranging from 150 to 370 watts per panel, depending on size. Higher-grade panels create more electricity from less surface area than lower-grade panels. So, if roof space is limited, or shading structures cannot be removed, a higher-efficiency panel may cost a bit more, but will produce more electricity from less space.
4. Buyback programs through your utility provider: In the vast majority of cases, solar works in partnership with the grid, which is essential to ensuring that your home has electricity even at night. Both electricity purchased from the utility, and electricity generated by your solar panels is measured by the same meter. The meter runs forward when being supplied by the grid, and backward when your solar PV system is generating excess electricity. In utility districts that support energy buyback programs (net metering), the homeowner has an opportunity to earn energy credits for their excess power. You can draw from these credits when you’re using conventional power, such as at night. With that said, determining how your local power utility provider calculates these credits is a critical factor in determining how many panels you buy. The more credits you want, the more panels you will need.