If you are researching a solar battery there’s one major question 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 an ever unsatisfying: it depends! The longer answer is a complicated one, 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.
Factors that influence how much of your house a battery can power
When talking about how much of your home you can power with a battery, the two main factors to consider are: how much power do you need, and how much power does your battery supply, with power measured in kilowatts (kW) or amps (A).
Don’t worry, we won’t bore you with technical details, we just want to make sure that if you are more familiar with amps or kilowatts, you can understand the other! Amps are a measure of current. Kilowatts are a measure of power. To get from current to power, you need to multiply by voltage. Homes in the US either have a 120 volt or 240 volt electrical panel, so to convert amps to watts, you just multiply the amps by the voltage (and then divide by 1,000 to get kilowatts): at 120 Volts, 20 amps of current would be 2,400 Watts or 2.4 kW of power. Easy, right?
Appliances/circuits you want to back up
To determine how much power you need, you need to 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 backup the whole electrical panel, providing power to every circuit at the same time, you would need a lot of power. As you’ll see in the next section, though, batteries typically provide far less power than that.
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 happen to know those values off hand, here are two resources to start with: first, our explainer on what even is 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.
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 it’s power requirements will drop for the rest of the time you’re running it. If you have an appliance that has a surge requirement for power when you first turn it on, be sure to look carefully at this spec.
Continuous power represents the amount of power (in kilowatts) that your battery can provide steadily. This is the metric to look at 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.
Factors that influence how long you can power your home with a battery
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 and which appliances you’re using, and for how long. But it’s also important to think about whether your battery is paired with solar, as well as if you are incorporating any load management systems along with your storage system.
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 is the case with your phone or computer, your battery will lose its charge faster when you’re doing more with the device.
Which appliances you’re using 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, that’s three less hours you can run your refrigerator. But if your plan is to keep the essentials–phones, computers, WiFi, refrigerator and some lights–running during an outage, you can expect a 10 kWh battery will keep those things running for nearly 24 full hours.
Whether your solar 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, so long as the sun continues to rise. 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.
Because batteries don’t have enough power output to backup your entire home at once, most storage installations include a critical load panel, a secondary electrical panel with fewer circuits that can be powered by a battery during an outage. The idea is that if you didn’t realize there was an outage, and tried to turn on your AC and your washing machine at the same time, it could damage many of the electrical components in your battery. So oftentimes, if you install a battery, you’ll have to decide which outlets, rooms, and appliances you want to back up with your battery for the lifetime of the battery.
But if you install your battery with a load management device–such as a smart electrical panel from Span, Lumin, Schneider or others, or something like Generac’s smart management modules–then you can let the software system efficiently and safely run your battery. No more need for critical load panels: you can keep every, or nearly every, circuit backed by the battery and the load management system will help you ensure you never overload the battery by turning too many things on at once during an outage.
How to calculate how much of your home you can run on a battery and for how long
Generally speaking, a battery with 5 kW of continuous power will be able to power a number of 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 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.
And, most importantly, you need to keep in mind how long you plan to use each appliance–the longer you keep each appliance on, the less amount of stored energy you’ll have to power other appliances to get you through the night or to 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.
Get storage quotes on EnergySage today!
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 go 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!