Fairfax County Dominion

Solar panels in Herndon, Virginia: 1,383 kWh per kW per year

A south-facing kilowatt of panels in Herndon makes about 1,383 kWh a year, 1.2% above the Virginia median. Power here comes from Dominion Energy at 15.20¢ per kWh (2025 average).

1,383

kWh / kW / year

PVWatts, south-facing

4.91

Peak sun hours / day

annual average irradiance

11,064

kWh / yr from 8 kW

a common home system

15.20¢

Dominion price

2025 residential avg

NREL PVWatts v8, 1 kW DC, fixed roof mount, azimuth 180°, tilt 25°, 14% losses. Jul makes about 1.8× Dec.

Seasonality

Monthly solar production in Herndon

Virginia net metering carries excess credits forward for 12 months, so Jul's surplus offsets Dec's shortfall. Systems are sized to annual usage rather than to the lowest month. How the calculator models net metering; the current rules by utility are on this Virginia incentives page, maintained by the installer behind this site.

Capacity factor: 15.8%. Elevation about 112 m. Compare every town on the city list, or see how roof direction, tilt and shade change the number.

Payback in Herndon

Solar cost and payback for an average home in Herndon

Assumes 1,038 kWh a month (≈ $158) at Dominion Energy's 2025 average price, Herndon's PVWatts production, 3% annual rate growth and $2.78/W installed, no federal credit. Dollars are nominal. Change any of it in the calculator, or compare every utility in Are solar panels worth it in Virginia?

Run it with your bill

9.0 kW

System size

$25,020

Est. cost

$2,072

Year-1 savings

11.1 yrs

Break-even

$61,907

25-yr savings

$36,887

Net benefit

undiscounted

Utility

Electric utilities serving Fairfax County

Utility	Type	Avg price ¢/kWh	Avg kWh / month	Data year
Dominion Energy	Investor-owned utility	15.20	1,038	2025*

Questions

Questions about solar in Herndon

How much electricity does a solar system produce in Herndon?

About 1,383 kWh per year for every kilowatt of panels on a south-facing roof, according to NREL's PVWatts. An 8 kW system would make roughly 11,064 kWh a year. East- or west-facing roofs make less; the calculator applies those factors.

Who is the electric utility in Herndon?

Dominion Energy serves Herndon, per EIA's service-territory data. Dominion's 2025 average residential price was 15.20¢ per kWh.

Is solar worth it in Herndon?

For an average Dominion home (1,038 kWh a month), the default assumptions give a 9.0 kW system costing about $25,020 with a break-even around 11.1 years and $36,887 net benefit (nominal) over 25 years. Your bill, roof and shade change that; the calculator lets you enter them. The statewide picture is in “Is solar worth it in Virginia?”.

Where does the sun data come from?

NREL PVWatts v8 (8.5.0), using the 1133773.csv typical-year weather dataset for grid cell 1133773, about 1 km from the town center. Inputs: 1 kW DC, fixed roof mount, 180° azimuth, 25° tilt, 14% system losses. Typical-year data doesn't change year to year.

Solar production in towns near Herndon

Sources: NREL PVWatts v8 (8.5.0, typical-year weather); EIA Form 861 2025 utility data and service territories; U.S. Census Bureau place coordinates. Formulas and assumptions on the methodology page.