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Batteries and what happens in a blackout
By the end: Distinguish energy shifting from backup capability and estimate a simple runtime.
A battery stores energy for later use. Its usable energy capacity is commonly stated in kWh; its power capability is stated in kW. Conversion and storage lose some energy. A battery might be operated to increase solar self-use, manage time-dependent prices, provide backup, or combine these goals.
Ordinary grid-following solar generally stops supplying the home when the grid fails. Backup operation requires a system designed to isolate from the grid and form a suitable local supply, with compatible controls and equipment. A battery on the equipment list does not by itself prove whole-home backup. Some specialized systems offer limited daylight backup; verify the actual design and limitations.
- Suppose 8 kWh is available to serve loads after the chosen reserve and assumed losses.
- At a steady 1 kW load, idealized runtime is 8 hours. At 2 kW, it is 4 hours.
- Also check instantaneous power and motor-start demands. A large kWh capacity does not imply unlimited kW.
- Real runtime changes with load, weather, operating limits, state of charge, and battery condition.
Diagram description
A designed backup system isolates selected home loads from a failed grid. Compatible PV, battery, inverter, and controls support those loads. Available energy and power both limit operation.
Quick check
What should you verify when a proposal promises “battery backup”?
End of module 2