Path-Q Solar
What battery size is appropriate when evening use is high but overnight use is low?
Answer
Size the battery primarily for the energy needed during the evening period, not for the entire night. Estimate the evening load duration, usable battery capacity after reserve and efficiency losses, and the power needed for simultaneous loads. A smaller battery may be sufficient if it can cover the targeted evening window and recharge reliably from solar or the grid under the intended operating strategy.
Key points
- Define the evening window and measure the energy used during it.
- Separate energy capacity in kWh from inverter power in kW.
- Account for usable depth of discharge, round-trip losses, reserve settings, degradation, and temperature effects.
- Compare a battery sized for typical evenings with one sized for high-use evenings or backup requirements.
What it depends on
- Evening load profile and duration
- Peak simultaneous power and startup loads
- Solar production and recharge opportunity
- Backup reserve and operating objective
- Battery usable capacity, efficiency, and degradation assumptions
Risks and trade-offs
- Sizing to occasional high-use evenings may increase cost and leave capacity unused most days.
- A battery with adequate kWh but insufficient kW may not run the intended appliances together.
- A battery sized only for bill shifting may not provide the desired outage backup.
Information you may need
- Interval electricity data
- Target evening hours
- Backup-load priorities
- Solar production profile
- Battery usable-capacity and inverter specifications
Your next step
What to do next
Request a comparison of battery sizes based on typical and high-use evening profiles, showing usable kWh, power output, reserve, recharge assumptions, and expected cycling.
Path-Q
Find the right next step
Answer a few questions and we’ll narrow your options.
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