Path-Q Solar
How should I size a battery if I want to cover evening electricity use?
Answer
Size the battery from the electricity you expect to use during the target evening window, then account for usable capacity, conversion losses, reserve limits, and the battery's power rating. Start with load data rather than choosing a battery only by its nominal capacity.
Key points
- Calculate the kWh used between the time solar production falls and the next meaningful charging opportunity.
- Use usable, not merely nameplate, energy capacity.
- Check that continuous and peak power ratings can handle the intended loads.
- Oversizing may provide little additional value if the battery is rarely cycled deeply or cannot be fully charged.
What it depends on
- Evening load profile
- Usable battery capacity and round-trip losses
- Solar production available for charging
- Desired reserve and operating strategy
- Battery power rating and system limits
Risks and trade-offs
- A battery sized for average evenings may not cover unusually high-use evenings.
- A larger battery costs more and may remain underused.
- Seasonal solar production can limit charging even when evening demand is unchanged.
Information you may need
- Interval electricity data by hour
- Desired coverage period and loads
- Battery usable capacity, power, and reserve specifications
- Solar production and charging assumptions
Your next step
What to do next
Build an hourly load-and-solar comparison for representative and high-use days, then request battery options that state usable kWh, kW output, reserve, and installed cost.
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