How long can you run your house on a Tesla Powerwall?

Picture this: The lights go out during a winter storm, but your home stays warm, your Wi-Fi keeps running, and your refrigerator hums along like nothing happened. That's the promise of the Tesla Powerwall, but how long can this battery backup actually keep your life running normally?

The short answer is just under 11.5 hours for the average home. But if you're strategic about what you power, that same Tesla Powerwall could last roughly two days. The key is understanding exactly how much energy your devices use and how the Tesla Powerwall 3 stacks up against your needs.

We figured out the Tesla Powerwall 3 can power the average home for about 11 hours and 25 minutes using this simple equation:

• (13.5 kWh / Avg daily home electricity use) x 24 = # of hours your Powerwall will run

For this calculation, we used the U.S. average daily household electricity use of 28.4 kilowatt-hours (kWh), based on the U.S. Energy Information Administration (EIA)'s most recently published report. Because the Tesla Powerwall stores 13.5 kWh of energy, we divide 13.5 by 28.4, which gives us 0.475 days. Multiply that by 24 hours in a day to get 11.42 hours—or roughly 11 hours and 25 minutes.

• (13.5 kWh / 28.4 kWh) x 24 = 11.42 hours

You can swap out the 28.4 with your home's average daily electricity use for a more personalized answer. To find yours, look at your utility bill. If it doesn’t outline your daily consumption, divide your monthly usage by the number of days in that billing period.

For a closer estimate, we’ve calculated how long the Powerwall would run the average home by region, using monthly (EIA) data.

How long the Tesla Powerwall 3 will run your house, by region

Not sure which region your state is in? Check out the chart.

Note: The average energy used per day is estimated based on annual averages, but energy use fluctuates by season, which will affect how long your Powerwall will last.

If you want a more accurate answer for how long your house can run on a Powerwall, you need to know two things:

• How much power you need for your devices

• How that compares to how much power the battery can provide

Battery capacity is measured in kilowatts (kW), while most of our appliances are measured in watts (W). Luckily, it’s easy to convert; just divide the watts by 1,000. For example, a 100 W television uses 0.1 kW. 

Energy (kWh) = Power (kW) × # of hours

•Most appliances cycle on and off, so their real draw is usually lower than their listed wattage. For example, a 500 W refrigerator actually uses closer to 167 W. You can divide your refrigerator’s wattage by 3 to estimate its real energy use.

With the exception of refrigerators, we used each device's listed wattage for our calculations for simplicity. But your devices will generally use a bit less electricity in practice, meaning your Powerwall will likely last a little longer than the numbers suggest.

To calculate how much power the Powerwall provides

All Powerwall models have a 13.5 kWh energy capacity, but this isn’t the only number we need to pay attention to. Home batteries have two other key metrics: peak power and continuous power.

• Peak (instantaneous) power is what it takes to start an appliance: For example, your fridge may need 500 W (0.5 kW) when first plugged in. If your appliances have a “surge” requirement, the battery’s peak power will need to be enough to cover that

• Continuous power is the maximum amount of power that the battery can supply on an ongoing basis, which tells you how many appliances you can keep running over time. For example, the 500 W fridge needs around 167 W (0.167 kW) to stay up and running.

The screenshot below compares the peak and continuous power ratings of the three Tesla Powerwall models currently on the market.

Screenshot from Tesla.com.

The Tesla Powerwall 3 has a continuous power output of 11.5 kW, meaning the battery can continuously run appliances that draw less than 11.5 kW for as long as the battery has energy. That rating is more than double the Powerwall 2's, and well above most competing home batteries, which typically land in the 5 to 8 kW range.

In plain terms: A single Powerwall 3 can run several appliances at the same time, while many other battery brands require multiple units to do the same.

To answer the “how long” question, you’ll compare the two factors:

• Usable storage capacity

• How long you're using each appliance

The usable storage capacity for a single Tesla Powerwall is 13.5 kWh. Functionally, this means you can use either 13.5 kW for 1 hour, 1 kW for 13.5 hours, or something in between.

(13.5 kWh / avg electricity use) = # of hours your Powerwall will run it

The big thing to remember here is that you'll probably be running a few of these at any given time, which changes the number of hours the Powerwall will last. For example, if you're running the refrigerator and you want to turn on the TV, this will eat into the amount of time you'll be able to run the refrigerator.

If the power went out and you couldn’t recharge your Powerwall, you’d probably scale back to the essentials. A Powerwall 3 running only your refrigerator, phone charger, Wi-Fi router, and five LED lights would last you roughly 58 hours—just over two days—on a full charge.

Up until this point, we’ve calculated how long a standalone Tesla Powerwall 3 lasts on a single charge. But if you pair it with solar panels, you can charge your battery almost indefinitely—even during a major outage—as long as the sun is out.

If one Powerwall 3 isn't enough, Tesla's Powerwall 3 expansion adds another 13.5 kWh without the cost of installing a full second unit. But most homeowners who add storage tend to install at least two batteries to meet their energy needs. Talk with one of EnergySage's free Energy Advisors to figure out how many batteries you'd need.