How Many Solar Panels Do I Need in District of Columbia?

19 panels of 400 W

A home using the U.S. average of 865 kWh a month needs about 19 panels of 400 W in District of Columbia, a 7.6 kW system, because each kW of panels produces about 1,391 kWh a year there (NREL PVWatts, south-facing roof).

Solar panels needed in District of Columbia by monthly electricity use (400 W panels)

Usage per monthPanelsSystem size
500 kWh11 panels of 400 W4.4 kW
865 kWh19 panels of 400 W7.6 kW
1,000 kWh22 panels of 400 W8.8 kW
1,500 kWh33 panels of 400 W13.2 kW
2,000 kWh44 panels of 400 W17.6 kW

Adjust the numbers

The calculator below is pre-filled with the numbers above. Change any value to match your project.

Solar system
kWh
Use the average of your last 12 bills if you can.
W
Most residential panels today are 350–450 W.
%
Solar panels needed19 panels of 400 W
System size
7.6 kW
Yearly production
about 10,572 kWh
Yearly usage covered
10,380 kWh
Production per kW in District of Columbia
1,391 kWh a year

What you will need

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How it is calculated

Yearly need = monthly kWh × 12 × the share you want to cover. System size in kW = yearly need ÷ the yearly production of 1 kW of panels in your state. Panels = system size ÷ panel wattage, rounded up.

Production per kW comes from NREL’s PVWatts v8 model for each state’s largest city, assuming a south-facing roof at 20° tilt and PVWatts’ default 14% system losses, as compiled by TheGreenWatt. For your exact address, run PVWatts yourself.

Open the full solar panel calculator for other shapes, a worked example and FAQs.

Other common sizes