What Size Solar System Do I Need for 500 kWh per Month?
Five hundred kilowatt-hours a month is a small bill next to the U.S. average, and it lands close to Hawaii's average month.
Full breakdown: what size solar system.
Panel-count context for a whole house: how many solar panels.
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Kilowatts, two ways
| Method | Array | 400 W panels, rounded up | Source |
|---|---|---|---|
| Phoenix year: annual kWh ÷ 1,755 | 3.42 kW | 9 | PVWatts v8 |
| 4 peak sun hours, then ÷ (1 − 0.14) | 4.84 kW | 13 | Battle Born hours; PVWatts v5 losses |
| 5 peak sun hours, then ÷ (1 − 0.14) | 3.88 kW | 10 | Battle Born hours; PVWatts v5 losses |
Panel counts round the unrounded kilowatts up on an illustrative 400 W divisor. For this 500 kWh month the Phoenix column is the 1,755 kWh per kW per year yield at lat 33.45, lon −112.07, tilt 20°, azimuth 180°, 14% losses.
How to size it
This bill is small enough that the two methods can be checked against Hawaii's annual total without leaving the EIA table. The steps themselves are the same pair used on every monthly page: a Phoenix year, then a 4-hour and a 5-hour day with default losses.
- Annual energy: 500 × 12 = 6,000 kWh.
- Phoenix array: 6,000 ÷ 1,755 = 3.42 kW. That 1,755 is AC kilowatt-hours per kilowatt of DC for the Phoenix inputs in the PVWatts v8 run. Unrounded, an illustrative 400 W panel count rounds up to 9.
- Daily energy: 500 ÷ 30 = 16.67 kWh. The 30-day step compares the bill with a monthly average; EIA does not print the number 30.
- 4 peak sun hours: (16.67 ÷ 4) ÷ (1 − 0.14) = 4.84 kW, which rounds up to 13 illustrative 400 W panels.
- 5 peak sun hours: (16.67 ÷ 5) ÷ (1 − 0.14) = 3.88 kW, which rounds up to 10 panels.
Set this beside the state range EIA publishes. Hawaii, the lowest state in that FAQ, used 6,178 kWh in the year. 6,178 ÷ 12 = 515 kWh per month, and 515 − 500 = 15, so a 500 kWh bill is 15 kWh under Hawaii's average month. The U.S. monthly figure is about 899 kWh, and 500 ÷ 899 = 0.56 of that average. Hawaii's annual energy on the same Phoenix yield is 6,178 ÷ 1,755 = 3.52 kW, next to this page's 3.42 kW for a 6,000 kWh year. Close, and not the same bill.
Here the 4-hour generic result (4.84 kW) sits above the Phoenix year (3.42 kW) because 4 peak sun hours is the low end of the baseline and dividing by (1 − 0.14) enlarges the array. Phoenix already folds in a December of 4.75 and an annual plane-of-array of 6.54. Take the address to PVWatts and the loads to the solar size calculator.
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FAQ
How many kilowatts offset 500 kWh a month in Phoenix?
6,000 kWh a year ÷ 1,755 kWh per kW = 3.42 kW. On an illustrative 400 W panel that rounds up to 9.
What do 4 and 5 peak sun hours give?
500 ÷ 30 = 16.67 kWh/day. (16.67 ÷ 4) ÷ (1 − 0.14) = 4.84 kW. At 5 peak sun hours the same steps give 3.88 kW.
How many illustrative panels is the generic high end?
The unrounded 4-hour result rounds up to 13 panels of 400 W. The 5-hour result rounds up to 10. The 400 W figure only turns watts into a whole-module count.
Does this replace a PVWatts run at my house?
No. 3.42 kW is 6,000 kWh divided by the Phoenix 1,755 yield (tilt 20°, azimuth 180°). A 500 kWh bill in another city needs its own run.
Related questions
- What size solar system for 1,000 kWh per month
- What size solar system for an average home
- What size solar system for 1,500 kWh per month
All of these questions are listed on the topic map.
Sources
- NREL/NLR PVWatts Version 8 API documentation — accessed Oct 2, 2026.
- PVWatts calculator — accessed Oct 2, 2026.
- NREL PVWatts Version 5 Manual, A. Dobos, September 4, 2014 — accessed Oct 2, 2026.
- Battle Born Batteries, How to Size Solar Panels for a Deep Cycle Battery System — accessed Oct 2, 2026.
- U.S. Energy Information Administration, How much electricity does an American home use? — accessed Oct 2, 2026.