Home batteries and backup

What Does a Solar-Plus-Battery Home Do From the Moment the Grid Fails Until Power Returns?

Published · By the SolarPanelX editors · Prices and specs as of that date, from the pages under Sources

Summary

Within seconds of losing grid power, a home PV system with battery storage can detect the outage and switch into an islanded mode that keeps the house running. That only works when the inverter is configured for it and a battery is present; panels alone shut off with the grid. When the utility restores service, the system reconnects on its own.

The first few seconds

DOE describes residential PV systems with battery storage that "automatically detect the loss of grid power and switch to an 'islanded' mode to keep the power on." Panels by themselves cannot do this because solar systems generally depend on the grid to produce power and are designed to switch off when grid power cuts out. Running independently takes two things, according to DOE: a properly configured inverter and a storage system. The inverter makes AC from the panels' DC, and the battery keeps power steady as solar output and household demand shift.

Through the night

In a long outage, solar and its storage can keep delivering power to homes, even at night. How long depends on two separate battery figures. Energy capacity is the total that can be stored, usually in kWh. Power capacity is how much can be released at a given moment, usually in kW.

A battery holding 10 kWh with a 5 kW output limit could, on paper, carry a fridge and lights averaging 500 W for 20 hours. Switch on the air conditioner, a microwave, and a kettle together for a 6 kW draw, and the same battery falls short on power while energy is still left in it.

When the grid comes back

Once the utility restores service, these battery-backed systems reconnect to the grid seamlessly, which DOE contrasts with diesel generators, the most common source of emergency backup. In everyday operation, solar can charge the battery in two ways, directly over DC or after being converted to AC.

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Sources

  1. U.S. Department of Energy — Solar and Resilience Basics
  2. U.S. Department of Energy — Solar Integration: Solar Energy and Storage Basics
  3. U.S. Department of Energy — Solar Integration: Inverters and Grid Services Basics

We have not tested these products. Specs, prices, stock and terms are as published on these pages on the date above and can change; check the manufacturer or retailer before you buy.

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