Path-Q Solar
How should a planned heat pump affect the size of my solar system?
Answer
Include the heat pump's expected annual and seasonal electricity use in the load forecast before sizing solar. The added demand can be substantial, especially for space heating in cold periods, but the correct increase depends on the home's heat loss, climate, heat-pump efficiency, backup heat, operating temperature, and controls.
Key points
- Use the heat pump's expected electricity consumption rather than its rated heating or cooling capacity alone.
- Heating demand often occurs when solar production is seasonally lower, so annual energy matching may not eliminate winter purchases.
- Backup resistance heat, if present, can materially increase peak and annual electricity use.
- Efficiency improvements to the building can reduce both heat-pump size and solar capacity needed to cover its energy.
What it depends on
- Home heating and cooling loads and climate
- Heat-pump type, efficiency, controls, and backup-heating strategy
- Current fuel use and the portion expected to shift to electricity
- Solar production by season and available roof area
Risks and trade-offs
- Sizing only from current bills may undersize solar after electrification.
- Sizing for all possible future heat-pump use may produce excess capacity if the project or operating pattern changes.
- Solar may offset annual energy without covering winter peaks or eliminating grid dependence.
Information you may need
- Heat-pump design or performance estimate
- Current heating fuel use and utility bills
- Home energy audit or heat-loss information
- Expected backup-heat operation and installation timing
Your next step
What to do next
Ask the solar designer to model current use, heat-pump use, and backup-heat scenarios separately, with monthly production and consumption shown.
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