Path-Q Solar
How should I account for a planned EV, heat pump, and electric water heater when estimating future electricity use for solar sizing?
Answer
Estimate each planned load separately using its expected operating conditions, then add those estimates to a normalized version of current household use. Use seasonal and timing scenarios because these loads can vary substantially with driving, weather, hot-water demand, controls, and backup heating.
Key points
- An EV estimate should include mileage, vehicle efficiency, charging losses, and charging schedule.
- A heat-pump estimate should reflect climate, building efficiency, setpoints, and backup heat.
- Water-heater use depends on household size, hot-water demand, unit efficiency, and operating mode.
What it depends on
- Equipment efficiency and capacity
- Climate and building envelope
- Driving distance and charging behavior
- Household size and hot-water use
- Whether loads can be scheduled during solar production
Risks and trade-offs
- A single annual average can hide winter peaks or periods when solar production is lower.
- Overestimating uncertain future loads may lead to excess capacity, while omitting them can leave the system undersized.
Information you may need
- Expected equipment models or performance assumptions
- Annual driving and charging pattern
- Heating loads, climate assumptions, and hot-water demand
- Current annual and seasonal electricity use
Your next step
What to do next
Build low, expected, and high annual-use scenarios for each planned load and have every quote use the same assumptions.
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