How much of my house can I run on a battery?

If you are researching a solar battery, there are a few major questions that you likely have: How much of your house can you power with a typical solar battery, and how long can you provide power to your home? As with most things, the short answer is ever unsatisfying: it depends! The longer answer is complicated, so we're here to help.

We've split this article into two separate questions–how much and for how long–since both questions are important as you decide which battery to install, but the answers rely on different factors.

When discussing how much of your home you can power with a battery, the two main factors to consider are:

• How much power you need

• And how much power your battery supplies

To figure out these details, it's helpful to have a working knowledge of two common electrical terms: amps and kilowatts.

1. Appliances/circuits you want to back up

To determine how much power you need, you must know which appliances (or circuits) you plan to back up. Many homes in the US have a 200 amp electrical panel. If you wanted to back up the whole electrical panel, simultaneously providing power to every circuit, you would need a lot of power. As you'll see in the next section, batteries typically won't cover those needs.

Thankfully, it's unlikely that you'll be running every single appliance in your home on any given day, and you're even less likely to be running all of them at once. Less excitingly, that means you (or your installer) will need to calculate the power usage of different appliances in your home or of different circuits on your electrical panel (most circuits can hold a max of 15 to 20 amps).

Batteries provide power ratings in kW and current ratings in amps, so if you know the power draw or current requirements of different appliances, you're in luck! If you don't know those values off hand, here are two resources to start with: first, our explainer on electrical load, and second, the US Department of Energy's appliance load calculator. By finding the wattage of each individual appliance, you can calculate the power requirements for backing up your home: 200 watts for a refrigerator, 20 watts per light bulb, 25 watts for a phone charger, 300 watts for a TV, and so on.

2. Power rating of your battery (instantaneous and continuous)

Once you know how much power you need to back up part or all of your home, you can begin to size an energy storage system appropriately. There are two key power metrics to look at: instantaneous power and continuous power. Instantaneous power determines if you can provide an extra surge of power to appliances that need it. For instance, a well pump or sump pump might require a lot of power when you first turn it on, but then its power requirements will drop for the rest of the time you're running it. If you have an appliance with a surge requirement for power when you first turn it on, look carefully at this spec.

Continuous power represents the amount of power (in kilowatts) your battery can provide steadily. This is the metric to determine how many different appliances and circuits you can power at once for hours at a time. Most batteries have a continuous power rating of between 5 and 8 kilowatts, meaning they could power several circuits or a handful of appliances concurrently.

When determining how long you can power your home with a battery, the primary factors to consider are the usable storage capacity of your battery relative to the appliances you're using, and for how long. But it's also important to consider whether your battery is paired with solar and if you are incorporating any load management systems along with your storage system.

1. Usable storage capacity of your battery

The first factor to know is how much electricity your battery stores. If you're looking at spec sheets or your storage quote (something EnergySage makes easy to do with our Buyer's Guide and our online comparison-shopping Marketplace), the metric to look for is usable storage capacity. Usable storage capacity is listed in kilowatt-hours (kWh) since it represents using a certain power of electricity (kW) over a certain amount of time (hours).

To put this into practice, if your battery has 10 kWh of usable storage capacity, you can either use 5 kilowatts of power for 2 hours (5 kW * 2 hours = 10 kWh) or 1 kW for 10 hours. As with your phone or computer, your battery will lose its charge faster when you do more with the device.

2. Which appliances you're using and for how long

When you know how much usable capacity your battery has and the power consumption of your appliances, the next step is to determine which appliances you plan to use and how long you'll be able to use them. If your battery has a usable capacity of 10 kWh, you can power a:

• 3,500 W air source heat pump for under 3 hours;

• 300 W TV for 33 hours;

• 200 W refrigerator for 50 hours;

• Five 20 W light bulbs for 100 hours;

• 25 W phone charger for 400 hours;

• Or a 6 W WiFi router for 1,600 hours.

You'll likely be running multiple appliances at once, which makes the backup calculation much more dynamic with many tradeoffs. For instance, if you turn your TV on for two hours, you can run your refrigerator for three fewer hours. But if you plan to keep the essentials–phones, computers, WiFi, refrigerator, and some lights–running during an outage, you can expect a 10 kWh battery to keep those things running for nearly 24 hours.

3. Whether your battery is paired with solar

If you install a standalone battery, then in the event of a grid outage, you will have no way to recharge the battery until the grid service is restored. So if you experience frequent but short electricity outages, a standalone battery is a great way to keep your home running while your power is out. But if you experience longer-duration outages–reaching a day or more–a standalone battery isn't the right solution for backup power.

In that scenario, it's best to pair a battery with a solar panel system. When you pair solar with storage, you can provide backup power to your home indefinitely, as long as the sun rises. Even if you have a cloudy day or two, once the sun starts shining in full again, you can recharge your battery and keep your home powered even if the rest of your block remains stuck in the dark.

Generally speaking, a battery with 5 kW of continuous power will be able to power several different appliances at once: a refrigerator (800 W to start, 200 W to run), furnace fan for gas heat (600 W), cell phone chargers (25 W a pop), a WiFi router (6 W), a dozen light bulbs (21 W per light bulb, ~250 W total), a TV (300 W), and even a microwave (800 W) or coffee pot (900 W). Depending on what else you're running, you might even be able to run your washing machine (800 W) or a dishwasher (1800 W).

Can you keep your home climate conditioned off of a single battery? Maybe, but unlikely: a typical AC unit might have a power draw of 5 kW, while a more efficient air source heat pump could use closer to 3 kW of power to heat and cool your house.

Most importantly, you need to remember how long you plan to use each appliance–the longer you keep each appliance on, the less stored energy you'll have to power other appliances to get you through the night or the next sunny day. If you keep your TV on all day every day, it will use over 7 kWh of electricity per day, a significant portion of the typical 10 kWh of usable energy storage that many batteries have.

As you compare your battery options, check to see if the battery app (or an app from your inverter or smart electrical panel) will tell you how much battery life you have left under different usage scenarios & conditions.

If you're interested in a solar-plus-storage system for backup power, the best place to start is with custom quotes from local solar & storage companies. Look no further than EnergySage! You can sign up with just an email address, your physical address, and an estimate of your monthly electricity usage, and we'll get you custom solar & storage quotes from up to seven local installers. See how much you can save with solar–and back up with storage–today!