How to know how many solar panels do you need?

So you’re keen on going green and switching to solar power. A key question you will have to ask yourself at some point is: How many solar panels will I need for my home? This will, of course, depend on first knowing just what your overall goals are. Introspect a bit and ask yourself a few questions – are you trying to lower your carbon footprint and save the environment? Or save money and maximize returns on your investment? If you are like most people, you probably wish to save money whilst also reducing your personal impact on the environment. If that is your goal, then to work out how many panels you’ll require, you will need to know the following…

1. How much energy does your household use?

To work out your home’s energy needs look at your past utility bills. Look for the figure under “Kilowatt Hours (kWh) Used” or a similar figure – kilowatt hours measures the amount of power you are using at any given time times the total amount of time the power is used for. You are interested in daily usage, so if the bill doesn’t show an average for these figures, divide the monthly or annual averages by 30 and 365. That’s how much power your solar system will have to produce each day in order for it to supply 100% of your power needs.

Note: solar panels don’t work at maximum efficiency all or even most of the time. Bad weather or high cloud cover can severely reduce the efficiency of your system. Thus it is recommended that you add a 20-25 percent ‘cushion’ on top of your calculated daily average to ensure you get all the energy you need for your solar panels.

2. How much sunlight do you get in your area?

The number of peak sunlight hours in your area determines the amount of energy your solar panels will generate. This, in turn, depends on latitude, cloud cover, time of year etc. A useful resource here is the Renewable Resource Data Center that supplies information about the amount of sunlight you get in each state and major city of the United States. If you live outside the U.S, see if there is something similar in your own country. Having worked out this number, next multiply the hourly usage worked out above by 1000 to convert your energy requirements to watts. Then divide THAT number by the number of peak sunlight hours in a day in your location. That number, in turn, gives you the quantity of energy your solar panels will need to generate every hour in order to supply all your power needs.

3. How many solar panels will you need?

solar panels Not every solar panel is created equal. They come in different sizes, efficiency ratings ( ie. how well they convert sunlight into power), and utilize different cell technologies. Some panels just happen to be designed in a way that they absorb the available sunlight better than others.

Generally speaking, the more energy efficient your panels are, the more power (wattage) they produce, and the fewer you will need to put on your roof to get the same output of energy. To figure out the number of solar panels you will need, divide your hourly wattage needs (determined above) by the wattage of the particular solar panel you have in mind.

4. Other factors to consider

When selecting an appropriate solar panel for your rooftop, there are a few other factors to look at besides mere solar panel efficiency. For example, if you have a large roof area, with few shaded areas, the efficiency of the solar panel may not be all that important. To maximize sun exposure, and thus power produced, you may prefer to get MORE, cheaper panels (thus taking advantage of all the available roof space), even if they are not the most efficient ones out there. On the other hand, if you have limited roof space, with lots of shaded areas to boot, you will want a small number of highly efficient panels.

5. Next steps

Once you’ve worked out the number of panels you’ll need, call out a professional solar panel installer to assess the architecture of your roof, its position relative to the sun plus various other factors to determine if as well as how you’ll be able to physically fit the required number of panels on your roof and achieve your daily energy generations goals. If you are lucky, they will give you a free home solar evaluation.


Blogger, editor, developer who loves green living. Interested in photovoltaics and solar lighting. Reviewing solar products since 2013.

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