Updated: February 9th, 2020
The Tesla Powerwall 2 is one of the most advanced residential energy storage systems in the world, and the real magic behind it is the batteries. Tesla’s leadership in battery technology from the cell to the pack and into the finished products that utilize them highlights the fact that Tesla is truly not just an automotive company but really more of a broader tech company. Tesla’s batteries make their way from the company to consumers in a variety of form factors, including in cars like the Tesla Model 3 and stationary energy products like the Powerwall 2 and Powerpack.
Tesla has created a Powerwall Overview and Welcome Guide, but there are many features of the Powerwall that simply don’t come through in an introductory pamphlet. Digging deeper, Tesla published the AC Powerwall Owner’s Manual, which provides significantly more information for those willing or interested in looking behind the curtain.
The Powerwall 2 is, at its core, a DC energy storage system with a usable capacity of 13.5 kilowatt-hours per Powerwall. For more storage capacity, multiple Powerwalls can be installed in parallel. As most homes run on AC power, Tesla stacked an inverter on top of the battery pack that turns the stored DC power from the battery into AC power that all of the appliances and gadgets in the house can use. The inverter can push out the resulting AC power at 7kW peak or at a 5kW continuous rate. Bundling more Powerwall 2s together in a single installation also provides the capability to support even larger power draws.
Conversely, when it comes times to charge, the inverter can turn AC power back into DC power that is stored in the battery. This inverter has a round trip efficiency of 90%, meaning that 10% of the power sent into the Powerwall to be stored is lost by the time it gets back out due to the inefficiencies of converting the power from AC to DC (going into the Powerwall) and from stored DC power back to usable AC power as it comes out of the Powerwall into the home.
Batteries are commonly rated, compared, and discussed based on their usable capacity, as listed in kilowatt-hours (kWh). Unfortunately, the world of storage capacities is not a straightforward one, with some manufacturers listing the total capacity of the battery cells in the unit even though some of it might be reserved to protect the life of the battery.
Tesla lists the capacity of its Powerwall 2 units in terms of usable capacity, which is the total amount of energy stored in the battery that can actually be used by the homeowner. It features a 100% depth of discharge, meaning that the entire 13.5 kWh of usable capacity can be pulled out, if needed.
The Tesla Mobile App
The Tesla Powerwall can be managed from the Tesla mobile app, which is available in the Android and iOS app stores. This is the same app that Tesla vehicle owners use to monitor their vehicles, check on the status of vehicle charging, and check or conduct other vehicle functions. After logging into your Tesla account in the app, you can see the current state of charge of the Powerwall and change Powerwall settings.
On the energy side of things, the Tesla mobile app allows owners to monitor the energy flow between their rooftop solar systems, Powerwalls, the grid, and the energy usage of their homes. The real-time flow of energy is depicted with vivid graphics and animations that make it easy to see where different sources of energy are flowing and how much is moving around at any point in time.
Owners can dive deeper into the data to pull up detailed graphs for each energy source that shed insights on where large periods of consumption or generation are occurring within each unit. These trends allow owners to see solar generation and Powerwall charging patterns as they occur, and also focus their attention on energy usage within the home.
Tesla offers a video overview that walks through the core functions of its mobile app for Powerwall. It’s well worth the 6 minutes and change it takes to watch it if you’re in the market for a residential energy storage system and/or a rooftop solar system. Overall, the Energy section of the Tesla app provides the ability for owners to dig into the details of system operation and even select the operating mode for a Tesla Energy system.
In the next section, we’ll dive into the different operating modes owners can choose.
Powerwall Operating Modes
The Tesla Powerwall 2 was designed to allow for flexible operations with over-the-air updates that can push new functionality down to the Powerwall. The internet connectivity of the Powerwall Backup Gateway 2 allows it to stay connected to the internet to keep tabs on changing electricity prices, energy policies, and even the weather. These data are rolled together into a package that is constantly working to optimize the energy footprint of the home using a handful of optimization features.
Self-Powered — In this mode, the Tesla Powerwall 2 will maximize the self-consumption of an onsite solar system by the home. It does this by storing up power generated by the rooftop solar system during the day and using the stored power as needed to power the home. Tesla estimates that the ability to store daytime solar generation and use it back from the battery at night roughly doubles the amount of solar energy that directly powers your home. In this mode, the homeowner is also able to select the minimum amount of power saved as a reserve in the event of a power outage as a percentage from 0–100%.
Backup-Only — As a residential battery, one of the primary functions of the Powerwall is to provide backup power in the event of a utility power outage. In the event the outage lasts for an extended period, the Powerwall 2 can actually recharge itself from a rooftop solar power system. The capability means that while your neighbors might be without grid power for hours, days, or even weeks, a solar-connected Tesla Powerwall 2 system can effectively keep your home powered indefinitely, within the constraints of the size of the solar system and the number of Powerwalls installed, of course. In this mode, the amount of stored energy reserved for backup power can be set as a percentage from 0-100%.
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Advanced Time-Based Control — The Tesla Powerwall 2 is connected to the internet and has brains to match, which works to optimize the cost of energy for customers with electricity rates that vary depending on the time of day or the season. With Advanced Time-Based Control, the Powerwall 2 actively works to maximize the value of the solar generation and the energy usage of the home from the grid to intelligently charge and discharge based on the time and price of energy.
When connected to an onsite solar power system, Advanced Time-Based Control can operate in either a balanced mode or a cost saving mode. Balanced mode prioritizes using stored solar power to power the home when electricity is expensive and from the battery after the sun goes down. Cost-savings mode, on the other hand, optimizes the storage and usage of electricity to minimize the usage profile of the home to keep the cost as low as possible, maximizing savings that come as a result of having residential energy storage. Head over to Tesla’s Powerwall with connected solar system page for all the juicy prioritization details. It’s like a game, and Tesla is better at it than you are.
The Tesla Powerwall 2 has a handful of special modes of operation that solve for some of the more unique use cases. Those currently include Grid Services, Storm Watch, and Preconditioning, but more may be added with over-the-air updates in the future.
Grid Services — Powerwall customers participating in Grid Services programs now know when their systems are benefiting the grid and can track Grid Services energy and power usage. Grid Services are only available in areas where the utility offers a program so it will not show up as an option in the app for all Powerwall 2 owners.
Storm Watch — Storm Watch automatically detect incoming storms and prepare for them by keeping energy stored in the Powerwall. For Powerwall customers with backup and in selected regions, Tesla will automatically detect incoming storms and charge the Powerwall up completely to ensure power is available in the event of a weather-related grid outage. Owners can manually turn this off from the app, if desired.
Preconditioning — The Tesla Powerwall 2 is the only residential battery system on the market today that offers a full liquid thermal management system, according to Tesla. That translates to a completely sealed, liquid coolant system that circulates the 2.3 L (2.4 quarts) of liquid coolant in Powerwall throughout the battery array to ensure they are operating at the ideal temperature.
This integrated thermal management positions the Powerwall 2 uniquely in the market with its ability to operate at the widest range of temperatures compared to the competition, functioning from -4°F to 122°F.
If temperatures drop below freezing, the Preconditioning feature of Powerwall slowly begins to warm the battery to enable improved operation of the unit and charging performance of the battery. This happens automatically as Powerwall detects temperature changes.
On a daily cycle, Powerwall also begins to warm up the battery a few hours before sunrise after a cold night, in preparation for receiving a charge from the attached solar system. This ensures that it is able to soak in as much energy from the solar system when the sun comes up and the panels start cranking out power. Preconditioning can sometimes be seen on the Powerwall Power Flow screen in the app, which may show energy flowing to the Powerwall from solar and/or the grid. It is essentially invisible during normal operation and cannot be turned off.
Tesla implemented intelligent self-management of thermal loads to ensure that Powerwall 2 is always optimized to perform at its peak given the ambient conditions and anticipated conditions. Head over to the information page for the Powerwall’s special operating modes to learn more.
Powerwall Gateway 2
None of these tasks would be possible without internet connectivity, and it is the Powerwall Gateway 2 that makes that possible. The first generation of the Powerwall Gateway was little more than a fully connected computer housed in a rather boring looking grey utility box. Two antennas poked out the top of the box with one dedicated to increasing the reliability of the cellular data signal and the second for the connection to the home’s wifi network. A hardwired ethernet connection provides a third option for internet connectivity, just in case.
Tesla’s Gateway is currently being upgraded to version 2, which enabled Tesla to further standardize the way its Powerwalls operate on the wide range of grids around the world. The new Gateway 2 was rolled out as part of a larger standardization effort across the Powerwall product line that also saw Tesla increasing the pricing on the base Powerwall 2 unit and some of the other supporting hardware. Tesla started rolling out the Gateway 2 to early customers at the end of 2019 as a way to train up its installers, with a wider rollout planned for 2020.
The most noticeable change with the new Powerwall Gateway 2 is an all new Tesla-branded enclosure that will result in a much cleaner looking installation. It looks like a mini Powerwall and keeps everything looking crisp and clean though just about anything would be an improvement on the boring grey boxes they typically use.
The refresh of the Gateway shows just how critical it is to a Tesla Powerwall installation, and how important internet connectivity is to most of Tesla’s products as they strive to stay up to date and maximizing their benefit in the ever-changing landscape of electricity rates around the world. To learn more about the Powerwall Gateway, check out the product data sheet.
The Network Effect
The Tesla Powerwall 2 is a powerful energy storage appliance on its own, but that power is scaled up with Tesla’s ability to bundle Powerwalls together virtually into larger energy storage units. Imagine, if you will, bundling the Powerwall energy storage of 100 homes together into a single virtual unit with a usable storage capacity of 1350 kWh, or 1.3 MWh. Tesla is doing this at a massive scale in South Australia, where it aims to connect tens of thousands of homes together as a distributed virtual power plant.
This is the essence of what Tesla and others call a Virtual Power Plant (VPP), and Tesla is already doing this in production at a much, much larger scale than just 100 homes. In parallel to its blockbuster 129 GWh Powerpack installation, Tesla has partnered with the South Australian government on an initiative to install solar plus storage on a staggering 50,000 homes across the region to add yet another layer of distributed energy generation (DEG) and storage to the region.
The distributed nature of the installations increases the resiliency of the entire grid and all but eliminates the possibility that a single failure can take down the grid. Further, distributed energy storage is located in closer proximity to the point of generation and use, reducing the amount of energy lost in distribution and transmission.
Tesla’s Powerwall can be installed as a ground-mount installation or mounted to a wall, depending on what’s best for the location it’s being installed at. It is touch safe, meaning it does not need any special clearances nor does it come with any specific safety setbacks. The Powerwall is also water resistant and dust proof, making outdoor installations an option in most locations.
Powerwall and Backup Gateway units are rated for installation indoors or outdoors, and can operate within a wide range of temperatures, from -20°C to 50°C (-4°F to 122°F), though the optimum temperatures for Powerwall operation are between 0°C and 30°C (32°F to 86°F).
When it comes time for the actual installation, Tesla has outlined the process on its website, but look to an electrical professional to install it, as any type of incorrectly wired high-power devices can quickly result in a fire or other calamity. Have a look at the 2½ pages of warnings and safety notices in the Tesla AC Powerwall 2 Owner’s Guide for some of the specific risks beyond the obvious statements about not installing it areas that might flood. On that note, maybe a wall mount is the better option.
A Tesla Powerwall 2 might look like a cute, modern appliance that fits right in with the latest Apple, Google, and Amazon gadgets that
are listening to everything you do in your house are sprinkled around your home, but make no mistake, the Powerwall 2 is, at its core, a massive battery. Batteries are heavy and so is the Powerwall 2, tipping the scales at 122 kilograms (269 pounds).
At just 155 mm (6.1 inches) thick, the Powerwall 2 is much heavier than it looks like it would be, thanks to the bulk of the volume being filled with batteries. Overall, the Powerwall 2 has a footprint of 1150 mm x 755 mm x 155 mm (45.3 in x 29.7 in x 6.1 in), making it slender enough to mount to a wall without being obtrusive, but large enough to pack in some serious storage capacity.
On the wiring side, there are two primary configurations for how the Powerwall 2 is wired into the home. If the Powerwall 2 will only be used to provide backup power to essential loads in the home, a new sub-panel is required to connect the Powerwall 2 to the specific circuits in the home that will have power in the event of a grid outage, as depicted in the image below (new components in blue in both photos).
On the other hand, when the Powerwall 2 is wired into the entire home to be used as a whole home backup solution, it is wired directly into the main electrical panel of the home. In this configuration, only the Powerwall(s) and the Backup Gateway are added — a new sub panel is not required.
Energy storage is shaping up to be a mandatory component of that future, as it helps keep our locally generated renewables in our home, putting less strain on the grid.
The Tesla Powerwall can only be purchased and installed by approved installers, so the installed price can vary slightly. From a product side of things, Tesla lowered the price of the Powerwall 2 a few hundred bucks to $6,500 per Powerwall in mid-2019 though it’s worth planning for the additional $1,100 for the requisite Powerwall Backup Gateway 2 for any installation.
That covers the hardware, while installation ranges from $1,000 to $3,000, depending on the complexity of the installation. For example, if a Powerwall 2 is installed in conjunction with a rooftop solar system, the cost will be lower, as the electrician will already be onsite to do the wiring required for the solar panels.
A variety of rebates are offered by governments and utilities around the world that make the Tesla Powerwall 2 more affordable. Local electricity rates, residential energy storage regulations and pricing schemes also impact the payback on a Powerwall 2 installation, so some work may be needed to help price out the unit.
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