# Calculate Solar Array Size

• 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.??

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 realizethat you’re still “on grid” which means you’ll likely still use theutilities electricity a little bit.

Step 4: Array Size in kW = (Your kWh/year) / (365days/year) / (Solar Hours/day) * (Percent you want to cover) / (75%efficiency constant)

• Example: My electricity bill is ~\$110/mo and I use about900kWh/month. I live in SoCal so I get about 5.5 solar hours/day and Iwant 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.

Step 5: Calculate solar array size!

Source

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