If you’re considering installing a solar energy system, it’s likely you’re wondering just how big that system will need to be. The easiest way to visualize the size is to determine how many panels you need, and that number will vary depending on several factors.
Most homes require between 10 and 20 panels to completely offset their energy usage, which means your system is able to produce enough energy to support your daily usage. Some factors that come into play when determining how many panels you’ll need include the amount of sun your home gets, the tilt of your roof, how much energy you use, and the capacity of the panels you plan to install.
You can estimate how many panels you might need by running a few numbers. Of course, if the idea of doing this much math makes your brain hurt, you can schedule a consultation and leave the exact calculations up to the pros. If you’re up for a little algebra, here are the steps you can take to determine a ballpark number of panels your home might need.
A good formula to determine how many panels your home might need is daily electricity consumption / peak sun hours / solar panel wattage = number of solar panels. Here’s a step-by-step guide to find all the numbers and plug them into the formula.
The first step is to figure out your daily energy consumption. You should be able to find this on your energy bill. Your usage may vary from month to month, so the more bills you can find from the past year, the better. Once you have a few bills, add up their usage, divide it by the total by the number of bills to find the monthly average, then divide by the number of days included in one month’s bill to find your daily consumption. For context, one bill will usually cover about 30 days, but check the dates to make sure.
Next, you’ll need to determine the peak sun hours in your area. This number helps estimate how much sunlight your panels will get. There are a couple ways to find this number, and one is a bit easier than the other.
Footprint Hero offers a heat map and a calculator to help you estimate your peak sun hours. For the easy route, scroll to the bottom of the page to locate your area on the heatmap and use the scale to determine the estimated hours in your area.
If you’re up for a challenge, you can use the calculator for the estimate. This will yield a more accurate number because it takes more factors into consideration, but it’s a bit trickier because you’ll also need to know or estimate your roof’s pitch and Azimuth Angle. If you just want a rough estimate, we’d use the map.
The final number you need is called a power rating, which is the amount of energy each panel can produce per peak sun hour, as measured in watts. Take a look at the manufacturer details on the panels you plan to put on your home to find their power rating. Most panels have a 400-watt power rating, though your panels may have a bit more or less depending on your goals. Some homeowners opt for higher-power panels to optimize for smaller roofs, while others prefer lower-power panels to keep costs to a minimum.
Once you’ve got your numbers down, simply divide your daily consumption by peak sun hours then divide again by the power rating to estimate the number of panels you need for your home. For example, if we took the average numbers for each metric and plugged them into the formula, it would be 30,000 watt-hours / 4.5 peak sun hours / 400 watts for a total of 16.66, which you could round up to an estimated 17 panels.
Voila! You now have the formula to get a ballpark number of panels you might need for your home’s solar energy system. While this can be helpful to get an idea of how many panels you’re looking at, it’s important to note that the exact number of panels you need will vary based on the exact specifications of your home. The best way to determine your number will be to schedule a consultation with a professional. Check your home’s compatibility and find a solar pro in your area to get started.