How do I know what size solar PV system is right for my house?

MEP Solar
2

Sizing a PV system is not a trivial thing by any means. Your best bet is to gather your data (IE your annual kilowatt usage), and go to:

There you will find a calculator that takes all of the factors into consideration. This will get you in the ballpark for sizing.

3

To figure out what size system you need, you will need to know your electrical usage (kWh/year). The best way to find out your annual kilowatt usage would be to visit your electric service provider’s website and look for an option to view your usage or download your data. Then you can request solar quotes based on your actual usage. You can also visit Project Sunroof to get an idea of what size system you might need.

4

By offsetting the current or expected future, electric usage of the household. It is all about finding the kilowatts you need to produce.

5

If you are in SCE (Edison) Territory:

  1. Refer to page 1 of your electric bill.
  2. Look for the daily usage (in kWh) for the previous year(s). These figures are right above the chart in the middle of the page.
  3. Multiple that daily usage figure (for a typical home it could range from 10-50kWh/day) by 365 days/yr. That is your annual electricity usage (in kWh). (Go to Step 4)

If you are in LADWP territory:
1a. Refer to the electricity usage details on page 2.
2b. Add the bimonthly usage (in kWh) from the chart over the course over the last six billing cycles. That is your annual usage. (Go to Step 4)
3b. Another method is to average your usage over the last six (6) billing cycles and multiply by 2 to get your annual usage. (Go to Step 4)

(other utility bill should resemble either of the above)

  1. Go to pvwatts.nrel.gov. This is a Department of Energy site that has accurate projections for residential systems throughout the U.S. There are other sites, tools, and methodologies to determine optimal system size for your particular property, but PVWatts is a good resource and is usually all it takes.
  2. Enter your address. Then enter in a hypothetical system size, say, 7.0 kW. Decide if you’re going to use premium vs. standard panels, select roof mount (if on roof), and lower efficiency losses to 10-11% if using microinverters or to 11-12% if using DC optimizers. Then enter the orientation of your main roof area to be used with solar. If southward facing, enter 180 degrees (which is the angle from North). Then press ‘Go to Results.’
  3. If the result is lower than your annual usage (calculated in step 3), go back and increase the system size. Two or three trial and error attempts should have you zeroed in to the range you need.
  4. When your system size produces approximately what you use, the next step is to determine the power of the panels you want (in watts). If you decide to go with, say, SolarWorld 300W panels, and your system size was determined to be 9.0kW, you would need 30 panels to cover approx. 100% of your usage (and pretty much zero out your bill, except for residual monthly charges/taxes).
  5. Lastly, you’ll need to know if 30 panels will actually fit on your roof.

Typically, all of the above is the contractor’s job to walk you through. We started as DIY-ers, so appreciate the question!

6

The best way to do this is to speak to a solar professional with a proven track record. There are all kinds of calculators out there, but here is VERY BASIC way to calculate it. Calculate your KWHs that you use for 12 months and then divide by 12 to get your average. Take that number and divide it by 132. That will give you your approximate system KW size that you need. There are a lot of variables that come into play and you would never buy a system based upon this, however, this will be close depending on where and what direction that you put the solar panels. I hope that this helps.

7

asdf1234

8

You get a professional solar consultant to size up your roof to get the perfect size for your home.