Many homeowners ask whether adding rooftop solar panels lets them run a heat pump at no net cost.

The Short Answer: Yes, there are certain conditions when you can effectively achieve “free” daytime operation.

However, to make it a full-year with free heating or cooling is unlikely—unless you have a home battery storage system or an oversized PV (i.e. photovoltaic—the technology that converts sunlight directly into electricity). That said, what you can realistically expect is meaningful savings, especially in sunny, mild climates (Think: Southern California), and faster payback on your combined solar-plus-HVAC investment than on either system alone.

Why Pairing Solar With a Heat Pump is So Attractive

A heat pump moves heat using electricity rather than creating heat by burning fuel. Its efficiency is measured by COP (coefficient of performance—heat delivered divided by electrical energy used). A COP of 3 means the system delivers three units of heat for every one unit of electricity consumed. Because heat pumps run on electricity, rooftop solar directly offsets the largest portion of their operating cost: the compressor and fans. Contrast that with a natural gas furnace, where solar can only offset small electrical loads (fans, controls) but obviously cannot replace the fuel (gas) itself.

What “Free” Really Means — An Illustration

Imagine you have a 6 kW PV array on a sun-rich San Diego roof. On a clear midday it might produce somewhere in the broad range of 3–6 kW on average, depending on season, orientation, shading, and inverter losses. If your heat pump is running and consuming 2–3 kW at that time, the PV could cover it, making electricity for the heat pump effectively free while the sun shines. But mornings, evenings, cloudy days, and overnight demand mean that some HVAC energy will still come from the grid unless you add battery storage or significantly oversize your solar.

Anecdote: Midday Savings For A Working Couple

I recently helped a San Diego homeowner, let’s call her Ana, size a 7 kW PV system. On workdays her family was out during peak sun; they scheduled the heat pump to pre-cool the house in late morning and early afternoon when panels produced the most. Over summer, because Ana kept the house cool by running it off the solar even when they were not home, she reported that much of her air-conditioning energy was covered by solar and her midday consumption and her bills dropped dramatically. Evening cooling and occasional cloudy stretches still drew grid power, so the system wasn’t truly free 24/7. But the evening consumption was still much lower because the house had been kept cool all day thanks to the solar.

Real Savings and How to Estimate Them

To estimate savings, you need three pieces of information:

1. How much your PV produces (kWh/year),
2. How much energy the heat pump uses (kWh/year), and
3. How much of the heat pump’s use aligns with PV production (self-consumption).

Because rates, climate, and equipment varies, I’ll share reasonable ranges rather than single numbers:

1. PV production: A properly sized rooftop PV system in a sunny region often produces roughly 900–1,600 kWh per kW of installed capacity per year (wide range due to climate, tilt, shading, and system losses). For example, a 6 kW system could yield roughly 5,400–9,600 kWh/year.
2. Heat pump consumption: A whole-house heat pump used for both heating and cooling might consume anywhere from roughly 2,000 to 8,000 kWh/year depending on house size, insulation, thermostat settings, and climate. A small, well-insulated house in San Diego will be at the low end; a larger or poorly insulated home will be at the high end.
3. Overlap (self–consumption): Without batteries (see sidebar: Home Battery Storage Systems) and with typical household loads, homeowners often self-consume roughly 20%–60% of PV production, higher if you shift HVAC and other loads to daylight hours. With deliberate load management (smart thermostats, scheduled pre-cooling) you can push self-consumption toward the higher end. Adding a battery can increase daytime-to-evening coverage but adds the upfront cost of buying the home battery system.

Putting those ranges together gives a practical sense of savings. If a 6 kW PV system delivers 6,000 kWh/year and your heat pump uses 4,000 kWh/year, covering 50% of consumption with PV would offset 2,000 kWh of HVAC use. Multiply that by your retail electricity rate to get yearly savings. If your rate is $0.25/kWh, 2,000 kWh saved is $500/year. That’s a concrete, conservative way to estimate benefit without overstating.

Payback Considerations: Combined System Economics

Payback depends on system costs, incentives, and how much solar offsets HVAC electricity. Typical installed PV costs (after taxes and depending on local incentives and installer) can range widely; in many U.S. markets recent installed prices (before incentives) often fall in the range of about $1,200–$3,000 per kW installed for small residential systems, but local installer rates, permitting costs, and component quality change that range. Heat pump installation costs also vary widely—often roughly $3,000–$18,000 depending on system type (ducted vs. ductless, variable-speed, and the condition of existing ductwork). Because of variability, run payback using high/low estimates for both PV and heat pump costs and include available rebates or tax credits.

Example Payback Scenario

To illustrate, assume you add a 6 kW PV system that, after incentives, costs $8,000–$15,000 and produces 6,000 kWh/year. You also replace an old AC/furnace with a high-efficiency heat pump costing $8,000–$14,000 that reduces HVAC energy use by 30%–60% compared with the prior system. If solar covers half the heat pump’s yearly electricity, and electricity costs $0.20–$0.30/kWh, annual HVAC savings from PV might be roughly $300–$1,000 per year. Under these broad assumptions, simple payback on the solar portion for HVAC savings alone could be in the many-year range; when you include total household offset and other benefits (EV charging, lighting, resilience with batteries), the combined system often becomes more compelling. But keep in mind: The exact payback depends heavily on the current incentives, system sizing, and how much of your daytime use you can shift to solar production.

Cooling (AC) loads and PV Timing

Air conditioning tends to align well with solar production on hot, sunny days because that same hot sun that creates AC demand also generates PV. That happy coincidence improves the fraction of cooling energy a PV array can cover. In contrast, heating demand often peaks in mornings or evenings. However, in mild climates like San Diego, much heating demand is low and daytime heating or pre-heating strategies can capture more PV.

Practical Strategies to Maximize Solar Coverage of Your Heat Pump

• Time-shift HVAC: Pre-cool or pre-heat during peak sun so the house coasts through late afternoon or evening. You’re basically programming your HVAC system to turn on and either heat or cool the home during peak sun hours even if you are not yet home. This will reduce the demand later when you are home, but the sun is no longer shining
• Smart controls: Use thermostats and home-energy systems that prioritize solar consumption for HVAC and EV charging.
• Right-size PV: Install enough PV to cover a large share of daytime HVAC and other loads, but avoid gross over-sizing that wastes roof area or forces poor financial returns.
• Consider batteries selectively: Batteries increase the portion of HVAC energy supplied from solar during the evening and overnight, but they add upfront capital cost. A cost-benefit calculation should compare battery expense versus expected electricity-rate arbitrage and outage value.

Common Pitfalls and How to Avoid Them

A common mistake is assuming PV will cover all HVAC energy simply because the panels produce a lot of electricity annually. Timing matters. Unless you have a home battery system to convert and store the solar power, evenings and cloudy days will still force your HVAC system to draw from the power grid.

Another pitfall is underestimating heat pump sizing and duct losses. Poorly sized equipment or leaky ducts can raise energy use and reduce the fraction of HVAC energy covered by PV. The antidote is a Manual J load calculation (size the system to the home) and a thorough assessment of ductwork or consideration of ductless mini–splits.

Final Takeaway

You can often run a heat pump for “free” during sunny daytime hours when your PV is producing, and with smart controls you can substantially increase that fraction. Over a year, solar-plus-heat-pump systems usually produce clear, measurable savings.  This is especially true when cooling load aligns with PV production and when incentives lower upfront cost. But full 24/7 free operation is rare without a home battery system, and payback depends on local incentives, system costs, and how much you can shift HVAC use into sunny hours. Use conservative ranges for production and consumption when estimating savings, get professional load calculations and installer quotes, and include incentives to avoid surprises.