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How Many Solar Panels Do I Need?

How to calculate a quick, easy GUESStimate for sizing a PV system.

“How much will it cost to power my XX,XXX square foot house?”
“How many solar panels do I need to eliminate my electric bill?”

We get questions like this every day from homeowners in the beginning stages of going solar.

For all intents and purposes, it’s pretty much impossible to give you a number based on the size of your house or the dollar amount of your electric bill – it’s all going to depend on the load.  Though I hesitate to give a rough number like this, sometimes you do need a ballpark figure to start things off.

Alright, here we go:

To begin, calculate your average energy usage in kWh.  Collect your electric bills for the past 12 months or more.


Get an average of kWh used on a monthly basis.  Let’s say that this number is 1100 kWh per month.

Now divide your average monthly usage by 30 to get your average daily kWh usage.  In this case, it would be about 37kWh per day.

To keep things simple for this rough estimate, we’ll assume that a 250W solar panel will produce about 1kWh a day.  **Keep in mind that this is a rough estimate, based on a site location getting 4 hours of sunlight per day**

Assuming that you use about 37 kWh per day, you would need about 37 solar panels to meet 100% of your average energy needs.

Based on your current usage, how much of this do you want to offset with a solar power system?

100% …75%…. 50% ?    Multiply accordingly.

Let’s say you wanted your solar system to account for 80% of your energy consumption.

37 kWh per day x 0.80  = 29.6 kWh

Since one solar panel produces about 1 kWh per day, you would use 30 solar panels to account for 80% of your average consumption.

The purpose of this is to give a rough idea of how many solar panels you will need.  This sizing tool provides a quick number to go off of as you’re shopping around- it’s not a replacement for having an electrical contractor design a system for you.

Once you’ve calculated your average kWh use and determined the percentage that you plan to offset with solar, get a free solar quote from 😉  We’ll help you design a complete system that’s specific to your roof and geographical location.

Any questions?


Author: Tom Jackson

I believe clean, renewable energy is key to the evolution of society as a whole. Solar powers our planet, why not harness it to power humanity? Let's power our homes, our work, and our vehicles with solar energy. It begins with raising awareness and encouraging those around us to go green.

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