How to Calculate Solar Output Like the Pro’s

by Shawn | 2 Comments

So, you’ve got a few quotes from solar installers and want to know which solar power system will give you more energy / output / electricity. Let me teach you how to calculate solar output like the pro’s. This way you can double-check their quotes to know you’re getting a good deal.

  1. Get your quotes ready
  2. Visit the CSI online calculator
  3. Plug in the data
  4. Calculate!

Step 1: Grab your solar quotes and look for the specific solar module name and how many solar modules will be installed. Make sure you know the exact panel. Circle the panels and how many. Ex. 20 x SunPower SPR-200-BLK-U.

Then find the exact solar inverter in the estimate. This might be SMA SunnyBoy, Xantrax, Fronius, or Enphase. Circle this too. Ex. SMA SB4000US (240V).

Solar panel quote example

Lastly, find the part that says ‘First Year Expected Output’ or ‘Annual output estimate’. Circle this. Ex. 4,800 kWh/yr.

Solar output example

Step 2: Use the CSI EPBB solar calculator to double check your installer’s solar quotes. This is the same calculator California installers must use to calculate official numbers used in the rebate paperwork. It’s okay if you’re not from CA, see below.

CSI EPBB Calculator

Step 3: Plug in the numbers from above.

Don’t live in California? No problem, you can still get a rough idea, or at least numbers to compare. Use Zip Code: 94109, Utility: PG&E, and everything is else the same.

CSI Solar calculator Example Input

Step 4: Calculate and compare. Scroll all the way to the bottom and look for the part that says “Annual kWh” and the number across from it. This is how much actual electricity you can expect from your complete solar energy system in the first year. It’s measured in kWh (kilowatt-hours), the same as your electricity bill!

Solar energy annual output for 4 kW system

  • Jaia Brunt

    thanks for all this information. It has been invaluable for me to making a decision about which system to buy. THANK YOU

  • jessica

    You mentioned that we can also use the CSI EPBB Calculator even outside california. My question is the annual kWh result using this calculation is a way different than using PVWatt and any shading tool calculation. Using this calculation will give you a higher number results in kWh. Do you think the result is deceiving?…Which do you prefer results conservative values which closer to reality or higher value which not real?