Path-Q Solar
What information is needed to size a battery for my home's critical loads?
Answer
You need a prioritized list of critical circuits, each load's running and starting power, expected operating hours, the desired backup duration, and the battery and inverter's usable energy and power limits. Utility, panel, and installation information is also needed to determine how those circuits can be isolated and backed up.
Key points
- Identify what must operate, what is optional, and what should be excluded during an outage.
- Record running watts, startup or locked-rotor demand, voltage, and expected duty cycle.
- Determine whether loads can run simultaneously or be managed sequentially.
- Include battery reserve, conversion losses, recharge capability, and desired autonomy.
What it depends on
- Critical-circuit list and appliance specifications
- Desired outage duration and usage priorities
- Battery usable capacity and inverter continuous and surge ratings
- Electrical-panel configuration and backup architecture
Risks and trade-offs
- Appliance labels may not reveal actual startup demand or cycling behavior.
- Including large discretionary loads can make the battery much larger than necessary.
- A battery may have adequate energy but insufficient instantaneous power for motor loads.
Information you may need
- Recent bills or interval usage data
- Circuit directory, panel photos, and appliance nameplates
- Desired backup duration and load priorities
- Proposed battery and inverter specifications
Your next step
What to do next
Prepare a critical-load worksheet and have the designer verify both its energy calculation and its simultaneous and startup power calculation.
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SQ01635