Solar Panel Calculator for Washington, DC
Estimate the cost, savings and payback of solar panels in Washington, DC, using local NREL sunshine data, District of Columbia prices and electricity rates.
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Washington gets about 4.74 peak sun hours a day on a south-facing roof, so each kW of panels makes about 1,346 kWh a year. That ranks #71 of the 111 cities on this site. Output peaks in Jul and is lowest in Dec.
Sunshine in Washington by month
What an 8 kW system makes in Washington
| Month | Sun hours a day | Output | Bill savings |
|---|---|---|---|
| Jan | 3.10 | 656 kWh | $163 |
| Feb | 3.62 | 680 kWh | $169 |
| Mar | 4.67 | 944 kWh | $235 |
| Apr | 5.58 | 1,048 kWh | $261 |
| May | 5.83 | 1,104 kWh | $274 |
| Jun | 6.25 | 1,112 kWh | $276 |
| Jul | 6.26 | 1,136 kWh | $282 |
| Aug | 5.85 | 1,064 kWh | $265 |
| Sep | 5.12 | 920 kWh | $229 |
| Oct | 4.24 | 832 kWh | $207 |
| Nov | 3.46 | 672 kWh | $167 |
| Dec | 2.90 | 608 kWh | $151 |
| Year | 4.74 | 10,768 kWh | $2,677 |
Savings at 24.86¢ per kWh (District of Columbia average), with every kWh credited at that price.
Cost and payback by system size
At $3.20 per watt, the District of Columbia average, before incentives.
| System | Cost | Year 1 savings | Payback | 25-yr gain |
|---|---|---|---|---|
| 4 kW | $12,800 | $1,338 | 9.8 yrs | $18,729 |
| 6 kW | $19,200 | $2,008 | 9.8 yrs | $28,093 |
| 8 kW | $25,600 | $2,677 | 9.8 yrs | $37,458 |
| 10 kW | $32,000 | $3,346 | 9.8 yrs | $46,822 |
| 12 kW | $38,400 | $4,015 | 9.8 yrs | $56,186 |
How many panels you need in Washington
| Monthly use | System | 400 W panels |
|---|---|---|
| 500 kWh | 4.46 kW | 12 |
| 750 kWh | 6.69 kW | 17 |
| 1,000 kWh | 8.92 kW | 23 |
| 1,500 kWh | 13.37 kW | 34 |
| 2,000 kWh | 17.83 kW | 45 |
Covering 100% of a year's use at 1,346 kWh per kW.
Common questions
Is solar worth it in Washington?
At local averages an 8 kW system costs about $25,600 before incentives, saves about $2,677 in its first year and pays back in about 9.8 years.
How many peak sun hours does Washington get?
About 4.74 a day over the year on a south-facing roof at 20°, from 2.9 in Dec to 6.3 in Jul, according to NREL's PVWatts model.
How much does a 1 kW solar system produce in Washington?
About 1,346 kWh a year, or 112 kWh a month on average.
Is there a federal solar tax credit?
Not for homeowners who buy their system. The 30% Residential Clean Energy Credit ended for systems installed after December 31, 2025.
Sources
- NREL PVWatts V8 API (south-facing, 20° tilt, 14% losses, typical-year weather): https://developer.nlr.gov/docs/solar/pvwatts/v8/
- EnergySage, Solar panel cost by state (updated November 6, 2026): https://www.energysage.com/local-data/solar-panel-cost/
- U.S. EIA, Electric Power Monthly, Table 5.6.B (residential price, Jan–Aug 2026): https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_b