How much solar does a heat pump need?
Switching a typical house from gas to a heat pump adds thousands of kWh a year, most of it in winter when panels make least. Here is the math city by city. In a typical city that is about 10 extra panels (4.1 kW), or $10k–$16k added to the system price.
| City | Extra kWh a year | Extra kW | Extra panels | Added cost |
|---|---|---|---|---|
| Seattle, WA | 7,727 | 6.9 | 17 | $21k |
| Portland, OR | 7,054 | 6.0 | 15 | $18k |
| San Francisco, CA | 3,910 | 2.6 | 7 | $7,700 |
| Los Angeles, CA | 1,717 | 1.0 | 3 | $3,000 |
| Phoenix, AZ | 1,498 | 0.8 | 3 | $2,500 |
| Las Vegas, NV | 3,734 | 2.1 | 5 | $6,200 |
| Denver, CO | 10,558 | 6.6 | 16 | $20k |
| Salt Lake City, UT | 9,535 | 6.1 | 15 | $18k |
| Dallas, TX | 2,461 | 1.7 | 4 | $5,000 |
| Houston, TX | 1,130 | 0.8 | 2 | $2,400 |
| Minneapolis, MN | 11,269 | 8.6 | 21 | $26k |
| Chicago, IL | 7,978 | 6.4 | 16 | $19k |
| Detroit, MI | 8,281 | 6.7 | 16 | $20k |
| Atlanta, GA | 3,216 | 2.4 | 6 | $7,100 |
| Miami, FL | 0 | 0.0 | 0 | $0 |
| Charlotte, NC | 3,618 | 2.6 | 7 | $7,700 |
| Washington, DC | 5,458 | 4.1 | 10 | $12k |
| New York, NY | 6,278 | 4.8 | 12 | $15k |
| Boston, MA | 7,541 | 5.9 | 15 | $18k |
Assumes a 2,000 sq ft house; heating degree-days from NASA temperature data for the surrounding area (mountain areas read colder). South-facing roof, $3.00/W. Rough planning figures.
What the table doesn't show
Heat pumps use most of their electricity in winter, when panels make the least. In the north, summer surplus only pays for winter heating under net metering.
A heat pump also cools, replacing an air conditioner that would have used electricity anyway, so the real increase can be smaller than the table shows.
Also: How many solar panels does an electric car need? · How many solar panels does a pool pump need?