Path-Q Solar
How should I choose battery capacity if I mainly want to shift solar energy into the evening?
Answer
Size the battery from the amount of solar energy available after daytime loads and the evening energy you want to serve, then adjust for usable capacity, charging and discharging losses, reserve settings, and allowable depth of discharge. The best size is usually the one that captures useful surplus without being routinely underused or limited by battery power.
Key points
- Evening load after solar production ends is the main energy-sizing input.
- Usable capacity is less than the battery's nominal nameplate capacity.
- Battery power rating determines how quickly energy can be charged or discharged and whether simultaneous loads can be served.
- Seasonal solar surplus and evening demand should be modeled separately.
What it depends on
- Hourly household load and solar production
- Desired evening coverage
- Usable capacity, efficiency, reserve, and operating limits
- Battery cost, expected cycling, and electricity pricing
Risks and trade-offs
- A larger battery may provide little additional benefit if there is insufficient surplus solar to charge it.
- A smaller battery may leave evening demand uncovered but can have better utilization and economics.
- Battery degradation and replacement timing affect long-term value.
Information you may need
- Hourly load data
- Solar system size and production profile
- Desired evening loads and coverage period
- Battery usable capacity, power, warranty, and price
Your next step
What to do next
Model several battery sizes against hourly solar surplus and evening demand, including usable capacity, losses, reserve, cycling, and expected economic value.
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