How to Determine How Many Solar Panels Your Home Needs
In some ways, installing solar panels is different from other home improvement projects. Adding renewable energy to your home has a social benefit aspect to it as you use cleaner energy to power your lifestyle while reducing energy emissions and pollution. Solar energy can also directly impact your budget by lowering the price you pay for electricity.
But other than that, it’s like any other project: you need to set a budget for it. Installing solar panels can be an expensive undertaking. The average cost is around $25,000 , which is a significant price tag for most people. That’s why the first question you’ll have to answer when you decide it’s time to go solar is: How many solar panels do I need?
It’s not just about cost. The answer is critical in terms of every aspect of the project, from how much space you’ll need to ensuring there’s enough power from your panels.
Collect data
You’ll need all the high school math you thought you’d never need, because it’s time to do some calculations:
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Your energy needs. The first step is to know how much energy you need to produce. The average U.S. home uses about 11,000 kilowatt-hours (kWh) each year, or about 900 kWh each month. But this is just an average; your utility bill will give you a much more accurate idea of how much kWh of electricity you use each month. If you see 12 months of electricity consumption, you can average it to a number that accounts for seasonal fluctuations in electricity consumption. Then divide this average by 30.42 (the average number of days in a month) to get your daily usage information. For example, if you use 900 kWh per month, your daily consumption will be approximately 30 kWh.
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Exposure to the sun. The amount of sunlight your home receives each day is kind of the deciding aspect of solar energy. This varies greatly across the country, with areas in the southwest averaging around six hours a day and areas in the northeast averaging less than four hours (remember, these aren’t just daylight hours – cloud cover and weather conditions) . reduce the amount of sun exposure). Knowing how much sun you’re likely to receive will help you know how much energy your panels will need to generate on a daily basis. For example, if you need 30 kWh of electricity to power your home every month and you get an average of five hours of sunlight every day, then 30 kWh / 5 hours = 6 kWh needed every day.
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Panel power. The amount of energy that the solar panels you install can produce is critical. Most modern solar panels can produce 350 to 450 watts, or 0.35 to 0.45 kWh of electricity from the sunlight they receive. This is on average about 0.40 kWh.
Fill in the formula
Now that you have all the data, it’s relatively easy to calculate how many panels you’ll need. Formula
Daily kWh/kWh demand per panel
Using our numbers above (we need 6 kWh every day when using panels that produce 0.40 kWh), this means:
6 kWh / 0.40 kWh = 15 panels
When doing these calculations, it’s a good idea to round up so you end up with a little more than you need, rather than a little less. And keep in mind that a professional installer will make much more accurate calculations based on much more data (see below), so this number should only be used as a rough estimate to determine costs and feasibility.
Other factors
Your rough estimate will not be as accurate as a professional’s estimate; they will take into account what is called the production factor . The production factor applies to the entire system and ranges from 1 to 1.8 or so. For example, a 10 kWh system that produces 16 kWh of electricity would have a PR of 1.6. A 10 kWh system that produces only 10 kWh will have a PR of 1.0.
Production factor is a more complex calculation that includes not only the average amount of sunlight, but also the shade around your home, the orientation of the panels (which may depend on where you might place them), and the geographic features in and around your site , which may be affected by sun exposure and other factors. If the PR is lower than expected, you may have to add multiple panels to provide the required energy production.
Finally, be aware of the physical size of the solar panels and where they will be installed. Standard solar panels measure about 66 x 40 inches, give or take an inch or two, or about 17 and 7/8 square feet. If you need 15 of them, you’ll need approximately 268 square feet of space for them, so make sure there’s enough space in their intended location (your roof or yard if it’s an above-ground system).