Path-Q Solar
What battery size would support my essential appliances during a typical outage?
Answer
Battery size should be based on both the energy those appliances consume over the intended outage period and their simultaneous and startup power. List the essential loads, estimate their runtime, and separately check the inverter's continuous and surge ratings. A battery may have enough stored energy but still be unable to start or run a high-power appliance.
Key points
- Energy capacity is measured by how long loads can run; power capacity is measured by what can run at once.
- Refrigerators, pumps, compressors, and motors can have high startup requirements.
- Backup duration depends on weather, solar recharge, load management, and whether nonessential loads are excluded.
- Reserve settings and conversion losses reduce energy available to household circuits.
What it depends on
- Essential appliance wattage and runtime
- Simultaneous load and startup surge
- Battery usable capacity and inverter ratings
- Expected outage duration and solar recharge conditions
Risks and trade-offs
- Sizing for every appliance can make the system expensive and may reduce backup duration.
- Ignoring startup current can cause nuisance shutdowns or failed appliance starts.
- A typical outage may not represent a long outage or adverse weather event.
Information you may need
- Appliance nameplate or measured power
- Desired runtime and priority order
- Startup-current information for motors and compressors
- Battery and inverter continuous and surge ratings
Your next step
What to do next
Create a critical-load schedule with running watts, estimated startup watts, runtime, and priority, then have the proposed battery and inverter checked against it.
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