Path-Q Solar
How does running an electric water heater during daylight hours affect the amount of solar power I can use directly?
Answer
Running an electric water heater during daylight can increase direct solar use because the heater consumes electricity while the array is producing. The benefit depends on whether the heater operates during periods of surplus solar output and whether its controls can shift heating without reducing comfort or hot-water availability.
Key points
- The heater's demand can be supplied by solar instead of drawing from the grid when solar production is sufficient.
- A storage water heater can often provide useful load shifting by heating water during sunny periods.
- If the heater uses more power than the array is producing, only the available solar output is used directly and the remainder comes from the grid.
- Daytime operation may improve self-consumption, but it does not necessarily increase total annual solar production.
What it depends on
- Water-heater power and control schedule
- Solar production by time of day and season
- Hot-water demand and storage capacity
- Whether excess solar is otherwise exported or curtailed
Risks and trade-offs
- Heating water too early or too often can waste energy through storage losses.
- A control failure or unsuitable schedule could leave insufficient hot water later.
- The financial value depends on how exported solar is credited compared with avoided electricity purchases.
Information you may need
- Water-heater type, power rating, and operating controls
- Typical hot-water usage schedule
- Hourly or interval electricity and solar-production data, if available
- Rules and rates governing exported electricity
Your next step
What to do next
Compare the heater's operating schedule with expected solar production and determine whether a safe daytime or solar-surplus control schedule is practical.
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