Path-Q Solar
How large should a battery be to cover overnight electricity use?
Answer
Use the home's expected electricity consumption during the target overnight period as the starting point, then adjust the required nameplate capacity for the battery's usable-capacity limit, reserve setting, and discharge and inverter losses. Charging losses and daytime loads do not directly increase overnight storage needs, but they do affect how much energy and solar capacity are needed to recharge the battery for the next night. Use interval or time-of-use data rather than a daily average alone.
Key points
- Overnight energy need is the sum of expected loads during the chosen hours.
- Nameplate capacity is larger than the energy normally available for use because of reserve settings, usable-capacity limits, and discharge losses.
- Heating, cooling, water heating, refrigeration, and electric vehicles can dominate overnight demand.
- The battery also needs sufficient power output for simultaneous and starting loads.
What it depends on
- Overnight consumption profile and desired coverage hours
- Battery usable-capacity limits and reserve policy
- Inverter efficiency and output rating
- Whether available solar, after charging losses and competing daytime loads, can recharge the battery before the next overnight period
Risks and trade-offs
- Sizing to an average night may leave insufficient energy during unusually cold, hot, or high-use periods.
- A battery sized for energy may still be unable to start a large motor or serve all loads simultaneously.
- Full overnight coverage can cost substantially more than covering selected loads or peak-price hours.
Information you may need
- Interval electricity data or monitored overnight usage
- Target hours and loads to be covered
- Battery usable capacity, reserve, efficiency, and power ratings
Your next step
What to do next
Review interval usage for representative and high-use nights, calculate the required usable capacity and continuous and surge power, then separately confirm that the available charging source can replenish the battery for the next night.
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