Batteries: when they pay, and when they only keep the lights on
A Tesla Powerwall 3 stores 13.5 kWh and costs $13,000 to $17,000 installed. That buys a lot of peace of mind, and in some places some savings.
Backup: size it by what must stay on
List what you need during an outage. A fridge uses about 1.4 kWh a day, a gas furnace’s fan 3 kWh in winter, Wi-Fi half a kWh, LED lights a few tenths. Central air conditioning uses 20 kWh or more on a hot day, which is why "whole-home backup" usually means several batteries.
Two numbers matter: usable kWh (how long) and continuous kW (how much at once). Motors such as well pumps and air conditioners also need a surge rating. Try your own list in the battery calculator.
Savings: only under the right rules
With full net metering a battery saves almost nothing: the grid already stores your surplus for free. Under net billing or time-of-use rates, a battery stores cheap midday solar for the expensive evening, and recovers part of its cost. Thirty-seven percent of new home solar systems in 2025 came with a battery.
Portable power stations
A 2 kWh portable station (Jackery, EcoFlow, Anker SOLIX, Bluetti) runs a fridge for about a day and costs a fraction of a home battery. It will not power the furnace fan hard-wired into your house, and you have to plug things into it.
Watch: the best short video on this step
More in solar videos and resources.
Checklist for this step
- I have listed the appliances that must run in an outage
- I know their daily kWh and the biggest motor’s surge
- I know whether my rates make a battery pay (net billing or time-of-use)