Most solar installers will begin designing your system by looking at your annual kWh consumption so they can offset as much of that as possible. Your solar installer should look at current and future energy needs and maximize your roof space. 1kW of solar produces approximately 850kWhs of annual electricity. If you are wondering whether or not you have a good roof for solar, you can find that out HERE.
Your utility company charges you based on how many kWhs you consume in a given month. A kWh is a unit of energy. A kW is a unit of power. We will unpack that difference later. For now, you will want to log into your utility and see if you can find that number (kWh) for each month of the last 12 months. Write them down and come up with a total for the year. Some utilities will have a combination of natural gas and electricity. The only number you are looking for right now is that kWh number that tells you how many kilowatt hours you consumed.
To make the math easy, Let’s say that number is 6,000 kWhs in the last 12 months. Your avg monthly consumption is 500 kWhs though it may not work out that nicely. If you have natural gas for heat and electricity for air conditioning, your kWh consumption could be less in the winter and significantly more in the summer. In those cases, it is normal to over produce in the winter and use those banked kWhs in the summer when your air conditioning is running full tilt. That is called NET metering.
The next part of this math problem is to determine how much solar you would need to produce all of your kWhs from the sun. This exercise is more of an estimate but will help to set expectations. 1 kW of solar will produce about 850 kWhs of energy for your home per year. It will produce more than that in some regions like Arizona and less in others regions like Oregon. Take your annual kWh consumption and divide by 850 to get a rough estimate of what system size you will need. In this case, you would need a 7kW system. 6,000 kwhs per year / 850 kWhs = 7kWs. Avg system sizes vary by region but 7kWs to 8kWs is a good national average.
Great, now we are getting somewhere, but we are not done yet. You also want to consider future consumption needs. Do you have an EV yet? We’re all going to have one eventually. It takes 3kWs of solar on average to keep an electric vehicle “fueled” up and ready for a daily commute. Now is the time to consider adding enough solar to meet those future needs. Did you know the average US homeowner is consuming MORE power every year? Yes our appliances are getting more efficient but we’re just plugging in so many more of them. More often than not, your available roof space will be the limiting factor. In our example above, if you installed 7kWs to cover your current consumption and another 3kWs to plan for future consumption, you would need roughly 1,000 sqft of ideal roof space to accommodate a 10kW system. This is where the conversation around product and technology becomes critical. Spoiler alert: Not all solar is created equal.
Finally, It is important to note that the actual solar panels come in many different shapes, sizes and power ratings. The math above suggested a 10kW system would cover the current and future electricity needs from solar power. The type and number of solar panels proposed will vary by installer but the actual system size should be similar.
