If you’re in the market for a Tesla Powerwall, or any solar battery, your biggest question is likely, “how much of my house can I run using this battery, and for how long?” While the answer depends on a number of factors specific to your household’s energy use, we’ve outlined some steps you can take to make an estimation.
We’ll begin with the “how much” question. To get to the answer, you really only need two pieces of information: how much power your home needs and how much power the Tesla Powerwall can provide. Then, you can compare the two to figure out how many of your appliances the Powerwall can run. Power on batteries like these is measured in kilowatts (kW) or amps (A). Amps are a measure of current, while kilowatts are a measure of power. Here is the simple equation to convert amps into kilowatts (to calculate watts, just skip dividing by 1,000):
Kilowatts = (amps x voltage) / 1,000
You can use this equation to calculate the amount of power you’ll need to supply each appliance, and then compare the total with the power output of the Tesla Powerwall.
How much power do you need?
To determine the amount of power you need, you’ll need to know which appliances you plan to back up. In order to figure this out, either you or your installer will need to calculate the power usage of the different appliances in your home.
To get started, we highly recommend taking a quick look at our article on understanding electrical load, in which we walk you through how to calculate the electrical load for your various appliances. By finding the wattage of each individual appliance, you can estimate the collective power requirement for your entire home.
How much power can the Powerwall provide?
Once you’ve figured out how much power your home uses, you can then compare this number to the power rating of the Powerwall. For batteries like the Powerwall, you’ll need to look at two ratings: instantaneous power and continuous power.
Instantaneous power is the power it takes to start an appliance: for example, the power required to start up your car engine. You’ll need a lot of power initially to get your machine started, but after the initial start the power draw will drop considerably. For your appliances, you’ll want to check if they have a surge requirement, as this metric will then come into play.
Instantaneous Power Rating of Tesla Powerwall = 7 kW
Continuous power is the power your battery can provide over a long period of time: for example, the power needed to keep your car running after it has been started. This will tell you how many appliances you can continue to run over a long period of time, say an hour or more.
Continuous Power of Tesla Powerwall = 5 kW
This continuous power rating is fairly standard for batteries of this kind, which typically range from 5-8 kW.
For the “how long” question, it once again comes down to two factors: usable storage capacity and the duration of time you’re using each appliance. Whether or not you have a solar panel system alongside your battery is also a very important consideration.
Usable storage capacity
The usable storage capacity is a measurement of how much electricity a battery stores. Usable storage capacity is listed in kilowatt-hours (kWh), since it represents using a certain amount of electricity (kW) over a certain amount of time (hours).
Tesla Powerwall usable storage capacity = 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.
Duration of time you’re using each appliance
Next, you’ll want to figure out which appliances you plan to use, and for how long. These calculations depend on the power consumption of your particular appliances; below are some common examples. With the Tesla Powerwall, you can power a:
- 3,500 W air source heat pump for just under 4 hours;
- 300 W TV for 45 hours;
- 200 W refrigerator for 67.5 hours;
- Five 20 W light bulbs for 135 hours;
- 25 W phone charger for 540 hours;
- Or a 6 W WiFi router for 2,250 hours.
The important 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 another room’s worth of lights, this will eat into the amount of time you’ll be able to run the refrigerator. It’s a good idea to figure out the power draw of the essential electronics you’d need in a blackout, such as your WiFi, computers, and refrigerator, and then calculate how long the Powerwall will last for you.
The final estimate
Ultimately, how much of your home the Powerwall can support–and the duration of time it can do so–depends on your specific combination of appliances. Like any other battery, the Powerwall has a limited storage capacity (unless you’re pairing it with solar!), which means there will be tradeoffs involved when using its power. If you’re using only the essentials, like your WiFi, phone, refrigerator, and some lights, you can expect the Powerwall to hold you over for around 24 hours during a blackout. Alternatively, if you’re adding in other electronics, like your TV or air conditioning system, this will cause the charge to last a fraction of this time. While your particular power needs may vary, around 24 hours for the essentials is a generally a good rule of thumb.
If at any point you’re concerned about the charge of your Powerwall, don’t worry! You can monitor the energy level in your Powerwall using the Tesla app, which also allows you to customize the energy use of your Powerwall for specific circumstances, such as maximizing protection during a power outage.
Get quotes on EnergySage
If you’re interested in a solar-plus-storage system like the Powerwall, be sure to check out the EnergySage Marketplace, where you can receive solar and storage quotes from the best local installers. You could save thousands of dollars and protect yourself from blackouts, all while doing something great for the environment.