Solar Plus Heat Pump: Sizing Your Array for an Electrified Home
Adding a heat pump moves your heating bill onto the electric meter. Plan the solar around the new load, not the old one.
By Piggies Air Conditioning HVAC Team · Updated · 6 min read · Heat Pumps & Electrification
The short answer
When a heat pump replaces a gas furnace, winter heating energy moves from the gas bill to the electric bill, so a solar system sized for the old usage comes up short. Estimate the new annual kilowatt-hours first, then size the array. Under California's net billing rules exported solar is worth far less than it was, so a battery and a time-of-use strategy are part of the design.
Start with the new load, not the old bill
Your SCE history shows the electric usage of a gas-heated house. Add the heat pump's expected heating energy, the heat pump water heater, and any EV charging, and you have the target. A good HVAC contractor can estimate heating kilowatt-hours from the load calculation and the equipment's efficiency rating; a solar installer then turns that into array size using your roof's orientation and shading. Ask for the site-specific production estimate rather than a rule of thumb.
Keep in mind that in our climate the heat pump's cooling season usage often matches the old air conditioner, so the net change is mostly the winter months.
Why net billing changes the design
Since 2023, new solar customers in SCE territory are on a net billing tariff rather than the older net metering. Electricity you export at midday is credited at a rate well below what you pay to import it in the evening peak. The economics now favor using your own production: run the heat pump water heater and pre-cool the house during solar hours, and store the rest in a battery for the evening.
- Pair the thermostat schedule with solar production: pre-cool from late morning through early afternoon.
- Schedule the water heater to run midday.
- Size the battery to cover the evening peak window on a typical day, not the worst winter night.
- A rate plan designed for electrified homes may fit better than the default; confirm current SCE options.
Sequence the projects
- Envelope first: attic insulation and duct sealing shrink the heat pump, which shrinks the solar array.
- Panel check: both the heat pump and the solar inverter need capacity; do one load calculation for the whole plan.
- Heat pump before solar, or at least designed together, so the array is sized for the real load.
- Roof condition: a roof near the end of its life should be replaced before panels go on it.
Permits and interconnection
Solar and batteries need a building permit and an interconnection agreement with SCE; the heat pump needs its own permit and HERS testing. Coordinating the two contractors avoids two electricians each assuming the other left room in the panel.
What to remember
- 1 Size solar for the electrified load, including winter heating.
- 2 Under net billing, self-consumption and a battery matter more than export.
- 3 Insulate and seal first; it shrinks both the heat pump and the array.
This guide is general information for homeowners in Baldwin Park and surrounding communities. Codes, rates and incentive programs change; confirm current terms with the agency or program before relying on a date or amount. For your specific system, book a visit or call us.
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