The Tesla Powerwall 2 is the second-generation home storage battery from Tesla that is designed, at the very least, to be a backup source of power when the grid goes down.
At its most effective the Powerwall 2 decreases your dependence on the grid by connecting to your solar system and storing energy that the solar panels collect. Your solar panels gather energy that powers the home during the day but when they shut off at night, the Powerwall 2 takes over with the energy that it has stored.
The Tesla Powerwall 2 has AC voltage 120/240 V with a split-phase feed type. But the battery itself stores energy as DC, not AC.
The first-generation Powerwall did not include a converter, you had to buy it separately. The Powerwall 2 however, does include a converter so that energy that goes into the Powerwall from the solar system is converted to DC and stored.
When the Powerwall is used to power the home, it converts the stored energy back to AC with a round-trip efficiency of 90%, according to the Tesla fact sheet. This means that the Powerwall loses about 10% of its power in the process of converting power from AC to DC and back again.
How Many kW is the Tesla Powerwall 2?
The Powerwall 2 can store a total of 14kWh of energy with 13.5 kWh of usable energy. The Powerwall reserves enough energy to turn the solar system back on in the event of a power outage where the battery has used up its stored energy.
The Powerwall 2 delivers 5 kW of max continuous charge and discharge and 7 kW of peak charge and discharge which amounts to about 10 seconds when the Powerwall is functioning as a backup off the grid.
If a home in America typically uses about 30 kWh a day, that means that the Powerwall 2 can power about half that amount. This makes the application of a single Powerwall better suited to emergencies or times of low energy use.
As a back-up source, whether charged by the solar system or the grid, the Powerwall is effective for powering some things the home needs for a limited amount of time.
Recognizing its limited capacity, Tesla built the Powerwall 2 to be connected with other Powerwall 2s, thus increasing the unit’s storage capacity and how much energy you can draw from it. If you want to run your home under normal circumstances off the grid, you will need about 2-3 Powerwalls connected together to do it.
What Does That Mean in Real Terms?
Let’s take a look at how many Powerwall 2s Tesla recommends for running a different array of lights and appliances in your home. Just note that the size of your home may change how this info plays out.
- One Powerwall 2 – This will get you the use of your outlets, lights, and appliances that run on 120 V.
- Two Powerwall 2s – With two Powerwalls you can add to the aforementioned items some large appliances, like an air conditioner (as long as it’s compatible and within reason—see below), an electric stove with range and oven, a well pump, and a Tesla EV charging station.
- Three Powerwall 2s – With three Powerwalls stacked together you can safely add a non-Tesla EV charging station, your pool equipment, and your electric water heater and dryer.
Again, depending on your usage, how efficient your home is, and how large your home is, the items listed above could change. On the other hand, you can stack up to six Powerwall 2s together.
What About the Air Conditioner?
If running your air conditioner is a big part of surviving power outages, then you need to be aware that your air conditioner can greatly affect how many Powerwall 2s you need.
In order to figure out what kind of impact your AC is going to have on your Powerwall usage, Tesla recommends that you start by identifying the rating of locked-rotor amperage. You can find this info attached somewhere on the outside of your AC unit.
You might find that it is listed as the same amperage of a running load, or the label might not have anything listed at all. If either of these is the case, you need at least 2 Powerwalls to back up your AC.
If you find that your unit’s locked-rotor amperage has a number associated with it, you can determine that number’s impact on your Powerwall usage by figuring out what kind of compressor your AC runs on. Relate the type of compressor with the rating to figure out how many Powerwall 2s you will need to back up your AC.
If you have a scroll compressor with an LRA rating of 139 or less, you will need two Powerwall 2s. If the rating is more than 140 or more, you will need at least three Powerwall 2s.
It’s the reciprocating compressor that really drives up the need for Powerwalls. If the LRA rating is 56-83 you will need 3 Powerwalls, 84-111 and you’ll need 4, and 112-139 and you’ll need 5. If it’s 140 or higher, you will need 6 or more.
If it’s likely that AC is going to be the biggest need, it’ll also be the biggest draw, so check yours out and be sure you know what you’re getting into.
Size and Shape
Owing to some design changes from the original Powerwall, the Powerwall 2 is more suited to integration. The original generation of Powerwalls had a sleek design with curved corners that looked really cool but was not very practical. The only storage option for the originals was wall mounting which could be problematic given their weight.
The Powerwall 2 has a more square, flat design that allows it to sit on the floor if need be and can allow for easy integration with other Powerwalls.
Of course, how many Powerwalls you want to integrate and the space where you want to put them has a lot to do with how they are mounted. But in general, you can stack them side-by-side or one in front of the other.
If you want to stack your Powerwalls one in front of the other, you will need to mount them on the floor with adjacent wall space.
If, however, you want to stack them side-by-by, you would need to mount them on the wall. However you decide to do it, you can connect up to 6 Powerwall 2s together.
The Powerwall 2 is just under 4 ft high (45.3 inches), just under 2 and a half feet wide (29.6 inches), and about half a foot thick (5.75 inches). So, in terms of size, it seems sleek and portable, but Tesla’s backup battery weighs in at 251.3 pounds.
Owing to the precarious nature of wall mounting, among many other requirements of code and technical knowledge, the Powerwall 2 must be professionally installed in your home by a certified installer.
So, when you’re tallying up the cost, be sure to include the cost of the installation which can vary depending on your home and the company installing it.
Other Differences Between the First Two Generations of Powerwalls
The Powerwall 2 has twice the storage capacity over the original Powerwall which means the Powerwall 2 is of greater service in an emergency. That potential doubles and triples and so on depending on how many Powerwalls you decide to stack together.
It’s difficult to get an exact cost on the Powerwall 2 because the prices that websites quote may depend on whether they are factoring in tax credits. More on that later, but for now, it’s worth noting that for greater storage and efficiency, the Powerwall 2 actually seems to be cheaper at a per kWh rate than its predecessor.
Different Ways to Setup the Powerwall 2
As a storage battery, the Powerwall 2 can integrate with both your solar system and the normal power grid, and you can use it to supplement your power needs in a variety of ways. Let’s take a look at a few.
Storage from the Grid
If you don’t have a solar system yet or feel it isn’t right for you, you can still set up a Powerwall as a back battery for those times when a storm blows a transformer and your neighborhood loses power, or when the grid is overtaxed, and you experience rolling blackouts.
To have your Powerwall 2 charging from your main panel allows you to store at least 13.5 kWh of usable energy, if not more, depending on how many Powerwalls you have connected.
Storage from Your Solar System
While the Powerwall 2 need not be exclusively used with a home solar system, it is certainly ideally suited to such a setup.
Think of it this way. Without the Powerwall, your current solar system setup is using the sun’s energy to power your home. Whatever that system generates that doesn’t get used is put back into the grid, sold to your region’s power company, sometimes at paltry rates.
Now, imagine you’re set up with a Powerwall. Instead of watching the excess energy go back to the grid, you are seeing that energy stays in your home for your use, however much you can hold. You can use it to power your home at night, or you can store it for power outages.
If you have multiple Powerwalls linked together, you could conceivably do both.
The point is that, with a Powerwall installed in your home, you have the ability to get more benefit out of your solar system by storing the energy it generates.
And once you fill up your Powerwall (or Powerwalls), then you can sell the excess back to the grid.
Different uses with Your Solar System
You can set up your Powerwall with your solar system in a couple of different ways, depending on what you want to achieve with the unit.
When you set up the Powerwall as a whole house backup you set it up off the main panel. while in the partial backup option, your solar inverter and Powerwall go into and come off of a subpanel with only the circuits that you want to back up.
We’ll get more into this later when we look at the Gateway 2.
In prior years, going solar meant giving your pocketbook a break from the strain of your local power company while also giving the grid a break from the strain of your home’s AC. The concept of a home battery that stores power is another big step toward actually reducing your dependence on your local power company.
The beating heart of the Powerwall 2 is its Lithium-Ion battery pack. While Li-Ion is more expensive at first than a lead-acid battery, it is also more efficient retaining a greater depth of charge, lasting longer than a normal lead-acid battery, and weighing a lot less.
Efficiency and the greatest range of use seem to have been on Tesla’s mind when designing the Powerwall 2.
The Powerwall 2 is both indoor and outdoor rated and able to operate in temperature extremes from -4 degrees F to 122 degrees F at an altitude of up to 9,843 feet. Even the recommended temperature range is a big range, from 32 degrees F to 86 degrees F.
You may wonder how it’s possible for the battery to operate in such a large spectrum of temperatures. The battery is completely sealed and cooled internally by liquid. It monitors its environment so when it gets too cold, the liquid heats up, and vice versa.
The Powerwall boasts worldwide compatibility and a 10-year warranty, which means that if your Powerwall drops below 70% storage capacity, it will be covered under the warranty.
The Powerwall 2 not only gives you direct access to the power your solar system generates, but it gives you control over how to manage that energy through the app.
Using the app, you can set your Powerwall 2 to four basic settings:
- Back-up in case of emergency
- Powering your home at night when your solar system stops generating
- Powering your home at certain high-cost times of the day as well as at night
- Powering your home during high peak hours by using energy that the battery has stored during off-peak hours
Additionally, within all these settings, you are able to select what amount of energy you want your Powerwall to save for emergencies. So, even if you are using a combination of Powerwalls to aggressively power your home at night or during high usage times, you can be sure to always have a reserve.
The app also gives you control with a few other pretty cool features.
It has a storm watch capability that allows you to track incoming inclement weather. If you see a storm that looks particularly strong, say one with high winds predicted, you can set your Powerwall to store as much energy as possible in preparation for the likely outage that is to come.
If you have a Powerwall in certain regions, Tesla tracks storms and stores up energy automatically.
With the app, you are no longer reliant on your energy company to track your energy, particularly as it relates to the grid. You can keep track of how much energy you are putting back into the grid, however, this function of the app only works in areas where power companies have these grid services available.
Because this app goes with you whenever your phone does, you can monitor, track, and change your Powerwall settings at any time and from any location. That means all the basic settings listed above as well as the unique storm watch and grid analysis are available to you when you’re not at home.
What makes this connectivity possible is the Gateway 2, an interface which is required to be installed with your Powerwall 2.
Like a literal gate, the Gateway is a guard point between your system and the grid. As with the Powerwall itself, Tesla did a complete overhaul of the Gateway from its predecessor.
The former Gateway ran a 2G ATT cell chip, whereas now it runs on an LTE. The Gateway connects with Wi-Fi, but the older model had some dropout issues because it only connected to 2.4 GHz.
The Gateway 2 now works in conjunction with both 2.4 and 5 GHz making it more versatile and solving the dropout issues that the older model had.
How It Works
In terms of function, the Gateway is the hub of the whole setup. It is the brain that collects the electrical inputs and directs the storage and usage of the Powerwall.
In this sense, it’s not unlike a normal electrical sub-panel (just cooler looking cause, hey it’s Tesla). The Gateway 2 can house three 2-pole breakers that connect to an internal bus, allowing you breakers for your solar panel and your Powerwall.
Depending on how you have the Gateway installed, you may be able to use it to monitor your consumption and interaction with the grid. This is a nice feature given the fact that many power companies don’t allow a customer’s consumption meter to be attached to its own locked equipment.
According to Tesla, there are a couple of ways to set up the Gateway and Powerwall 2 system.
Whole House Backup
If you want to backup your whole house, that means that you want the Powerwall to store energy for everything that draws from your main panel.
In this configuration, your solar inverter and your Powerwall would hook up directly to the main box, and the Gateway 2 would connect off the main box as well, but on the other side, as it were, setting up shop between your main panel and the power company’s utility meter.
If you are storing energy in multiple Powerwalls so that you can utilize all the things you would normally utilize at night or during a power outage, the whole house backup is the setup you would want.
Partial House Backup
If, on the other hand, you have a Powerwall 2 that you want to dedicate to run only certain circuits, your setup would look like the following.
Your solar inverter and your Powerwall 2 would connect to a sub-panel that carries only those loads you want access to in an emergency, and the Gateway would hook up between the subpanel and the main panel, allowing you to monitor the energy that the Powerwall is storing for those specific circuits.
Compatible with the Future
Finally, the Gateway 2 comes with the addition of multiple communication ports that can allow for more functionality in the future, as that functionality is made available.
While the day may come when there is a Gateway 3, having these additional ports means that you may be able to forestall the inevitable replacement by incorporating better functionality into your existing system.
This may look like being able not only to store energy and use it in an emergency but being able to determine how to use that energy by going into preset modes of operation for certain appliances.
When to Get a Powerwall 2
Speaking of the future, if you’re thinking of getting a Powerwall 2, it’s worth putting some thought into when and under what circumstances.
Combine with Solar Investment
Certainly, if you haven’t invested in solar and are about to do so, now is the time to get the Powerwall 2. It increases your investment, of course, but depending on how many you get, it may also double what you get from your solar system, if the Powerwall 2 is able to power your house during the night when the system is not generating energy.
The night is when most people without a battery back have to go back onto the grid. You could eliminate this need with a well thought out Powerwall set up. By reducing your dependence on the grid, you’re increasing your savings over the coming years.
Tax Credit Incentives
If you buy a Powerwall 2, you can qualify for a Federal Investment Tax Credit (ITC), but only if you use the Powerwall in conjunction with solar or another renewable power source. Also, you have to own your own solar system. It can’t be leased.
Given these stipulations, essentially, if your battery is charged by at least 75% renewable energy, then you qualify for a tax credit that is equal to what the battery gets from renewables. That’s a pretty good credit and worth keeping in mind.
But here’s the catch.
The ITC won’t be here forever. It is going to diminish sometime this year and it will go away entirely in 2022.
So, if you’re considering investing in a Powerwall connected to a solar system, time is of the essence if you want to get the most upfront savings possible.
Honestly, it’s an exciting time for solar-based energy. The possible benefits to the homeowner are increasing and the Powerwall 2 is a big part of why this is happening.
It represents a fundamental shift in dependence on the grid. It’s not likely that you will be able to go completely off it with a house that is already built and connected. But you can do a lot better than you were able to twenty years ago.
The Powerwall 2 is able to store 13.5 kWh as DC and convert it back to AC for your home with a round-trip efficiency of 90%. This means the vast majority of power goes to meet the needs that you have.
As an emergency backup, the Powerwall 2 is an ideal solution and can be configured to store power dedicated to certain circuits that you want to continue operating in the event of a power outage.
Or you can stack multiple Powerwalls together in either a side-by-side formation or a front-to-back formation to increase the amount of kWh you can store and the amount you can draw. Their redesign allows them to be floor or wall-mounted.
When you use multiple Powerwall 2s you can configure them to store energy for the whole house which you can draw on in an emergency or during the night when solar forces people without a backup battery to go back on the grid for power.
The Powerwall 2 is managed through the overhauled Gateway 2. With internet access, you can tweak the settings of Powerwall even when you aren’t at home. You can set it to back up power or use power from the Powerwall that you have stored to replace the energy that might otherwise be used during peak hours, thus saving money.
You can also use the storm tracker to help you prepare your backups for a possible power outage.
All this results in saved money for the customer. While the Powerwall 2 represents a hefty investment, especially if you are getting multiple units, the savings it provides the customer will reap dividends in the long run.