Path-Q Solar
How does electric water heating change the electricity demand a solar system should cover?
Answer
Electric water heating can materially increase household electricity use, so include its expected annual and seasonal consumption in the solar load forecast. The impact depends on the heater type, household hot-water demand, efficiency, temperature settings, recirculation, and operating schedule.
Key points
- Heat-pump water heaters generally use less electricity than conventional resistance heaters for comparable hot-water service, but actual use varies.
- A larger household or high hot-water demand can increase the load substantially.
- Timers or controls may shift some consumption toward solar-production hours without changing total demand as much.
- The water heater may create a significant load even when its annual energy use is predictable.
What it depends on
- Water-heater technology and rated efficiency
- Household size, hot-water demand, and incoming-water temperature
- Operating schedule, recirculation, and control settings
- Existing fuel use if water heating is being electrified
Risks and trade-offs
- Sizing only from the heater's rated power can confuse peak demand with annual energy use.
- Sizing only from annual energy can overlook electrical-service or peak-load constraints.
- Replacing a fuel-fired heater with resistance electric heating may increase demand more than a high-efficiency alternative.
Information you may need
- Current and proposed water-heater type and specifications
- Fuel or electricity bills and hot-water usage information
- Household size and occupancy pattern
- Planned controls and operating schedule
Your next step
What to do next
Ask the designer to include the water heater as a separate load in both annual solar sizing and electrical peak-load checks.
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