What Does a 15 kW Solar System Produce, What Does It Cost, and Which Homes Need One?
Summary
About 16,000 to 26,000 kWh a year, about $39,000 before incentives, and more than most homes use. PVWatts puts 15 kW at roughly 26,330 kWh a year in Phoenix, 19,370 in New York and 16,320 in Seattle. At EnergySage's 2026 average of $2.60 per watt that is about $39,000 installed, with no federal credit for 2026. The homes that use that much are at the top of EIA's survey: 3,000 square feet or more averages 15,489 kWh, and adding two electric vehicles brings it to about 21,440 kWh, which 15 kW covers 90% of in New York and 76% in Seattle. Four out of five systems installed in 2025 were about 12 kW or smaller.
Output and cost
| City | Annual output of 15 kW | Cost at $2.60/W |
|---|---|---|
| Phoenix | about 26,330 kWh | about $39,000 |
| New York | about 19,370 kWh | about $39,000 |
| Seattle | about 16,320 kWh | about $39,000 |
Output assumes a south-facing array at 20° with 14% losses. The price is the national average; EnergySage's state figures run from $2.12 per watt (Florida, about $31,800) to $3.84 (Alabama, about $57,600). With 430 W modules, 15 kW is 35 panels, about 735 square feet of roof before spacing.
Who uses 15,000 to 20,000 kWh
| Household, EIA RECS 2020 | Annual use | Share covered by 15 kW, New York | Seattle |
|---|---|---|---|
| 3,000 sq ft or more | 15,489 kWh | 125% | 105% |
| Six or more people | 14,730 kWh | 131% | 111% |
| Electricity as main heating fuel | 13,073 kWh | 148% | 125% |
| 3,000 sq ft or more plus two EVs | about 21,440 kWh | 90% | 76% |
The EV line uses DOE's 27 kWh per 100 miles and 11,026 miles a year per car, about 2,980 kWh per vehicle. For a house below these groups, 15 kW overshoots, and what the utility pays for the surplus decides whether the extra panels earn anything; our guide on excess power covers that.
Where 15 kW makes sense
- An all-electric house in the North with electric heat and two cars to charge.
- A large house in a hot climate with air conditioning that runs most of the year.
- A roof that can hold 35 panels facing roughly south.
Below that, LBNL's median of 7.7 kW and its finding that 80% of 2025 systems were about 12 kW or smaller are the better guide. Our companion guide works through what a home would have to use to match 15 kW.
Sources
- NLR Developer Network — PVWatts API Version 8 (runs by the editors, September 23, 2026)
- EnergySage — Solar Panel Cost in 2026 (updated June 30, 2026)
- U.S. EIA — RECS 2020, Table CE2.1
- U.S. DOE Alternative Fuels Data Center — Charging Plug-In Electric Vehicles at Home
- U.S. DOE Alternative Fuels Data Center — Average Annual Vehicle Miles Traveled
- Lawrence Berkeley National Laboratory — Distributed Solar & Storage 2026 Data Update
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