SRoeCo Solar

What size solar system do I need for my home? Though this is a complicated question, we have simplified it for you below. Follow the 5 steps to estimate what size solar system you might need. Then calculate how much it might cost to install the solar system!

Step 1: Look at your electricity bills and average out your usage to find “Your kWh/year”.

• kWh/year = Average Kilowatt Hours of electricity that you use in a typical year.
• Your bill may tell you your kWh/month. If your bill is ~$100/month, you might use ~1,000 kWh/month. If your bill is ~$200, maybe closer to 1,800 kWh/month.

Step 2: Look at the US Solar Map below to get the number of hours per day the Sun shines on your house.

 Alternatively, you can get the avg solar hours of the closest big city by looking at this chart (from BFM).

Step 3: What percent of your total electricity bill do you want to come from the Sun?

• If your budget is strong, 75- 100% is a good bet, but just realize that you’re still “on grid” which means you’ll likely still use the utility’s electricity a little bit.
• If your budget is limited, start with 50% and talk to your solar installer about leaving room for expansion later.

Step 4: Input the numbers in the calculator below. For those calculating by hand, the formula is:
Array Size in kW = (Your kWh/year) / (365 days/year) / (Solar Hours/day) * (Percent you want to cover) / (75% efficiency constant)

• Example: My electricity bill is ~$110/mo and I use about 900kWh/month. I live in SoCal so I get about 5.5 solar hours/day and I want to cover 75% of my bill!
• (10,800 kWh/year) / (365 days/year) / (5.5 kWh/day) * (75%) / (.75%) = 5.38 kW Array
• Due to real world efficiency losses (irradiance, dust, temperature, and wiring), you should expect your system power output (AC power) to be about 75% of the system (DC power) size. This is the .75 efficiency constant included.

Step 5: Calculate solar array size!

Step 6: Now estimate the cost of installing a solar PV system of that size with our Solar Cost Calculator.

Disclaimer: Material presented on the SRoeCo Solar website is intended for information purposes only. It is not intended as professional advice and should not be construed as such. Any use of the information and calculators on SRoeCo Solar for any purposes other than for a general overview or estimated results is not endorsed or encouraged.