Powering an entire home from batteries

What does whole house backup mean?

In a critical-load design, a backup panel carries a handful of circuits and everything else goes dark when the grid fails. In a whole-home design, the battery system sits between the utility and the main panel and feeds all circuits, so nothing needs to be rewired and the house behaves as it normally does. The convenience is real, since no one has to remember which outlets are live.

The price of that convenience is size. A house wired for 200 amp service can in theory ask for tens of kilowatts at once, and a battery system must be sized for what the house will actually pull, not just for what it normally uses. The introductory home battery backup guide covers the simpler design.

How much power and storage does a whole home need?

Two limits apply: how much power you can draw at one moment, and how long the stored energy lasts. A single battery and inverter may supply only a few kilowatts continuously, while a stove element, a dryer and a heat pump together can ask for more. Stacking units raises both power and storage, along with cost.

A worked example, with assumptions stated. Suppose a house uses about 30 kWh on an ordinary winter day, which is 1.25 kW on average. A 20 kWh battery would last roughly 16 hours at that average if the loads were steady. With electric heat, the average can double or more, and the same battery empties in half a day or less. These are illustrative figures; your utility bills show your real daily use, and an installer should size from them.

Which loads make whole-home backup difficult?

A few appliances account for most of the trouble.

• Electric space heating and electric water heaters. Large and often continuous, they drain a battery in hours.
• Central air conditioning. It has a high starting surge as well as a high running draw.
• Electric ranges, ovens and dryers. They are short but heavy loads that can trip an undersized inverter.
• Heat pumps in cold weather. They are efficient, yet they still draw several kilowatts on the coldest days.

Whether a home heats with gas or electricity changes the sizing a great deal; natural gas versus electric heating explains the difference in energy use. A house with a gas furnace needs only a small amount of electricity to run the blower, which is why it is far easier to back up.

Can smart controls make whole-home backup cheaper?

Often, yes. Load management devices let the system shed big loads automatically when the battery is low. The dryer waits, the water heater pauses, and the fridge, lights and furnace keep running. Some systems also let the owner set priorities by circuit from an app. This approach gives the experience of whole-home backup with a smaller battery, and it is a common compromise.

Another option pairs a battery with a generator that starts when charge runs low. The generator is run in short bursts rather than constantly. The trade-offs are described in solar generator versus battery backup, and the inverter side is covered by solar inverter types.

Is it worth paying for whole house backup?

For most households the extra cost buys comfort, not savings. It makes sense for rural homes with long outages, homes with essential electric loads such as a well pump and electric heating, or owners who want to run a home office or business without interruption. Elsewhere, critical-load backup plus load management usually delivers most of the benefit at a lower price.

Adding solar lets the battery recharge in the day during an extended outage, though winter output is modest; see solar panels in a power outage. Costs depend on region, year and installer, so rely on written quotes and the solar battery cost example for the structure of the numbers.

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