Case study: Tesla Powerwall installation

tesla powerwall case study

In 2017, EnergySage's former Vice President of Marketing, Luke Tarbi, installed a Tesla Powerwall 2 at his home in Vermont through Green Mountain Power's partnership with Tesla. In this case study, he shared his experience with the program.

We'd just closed on the house in Southern Vermont. Fortunately, the sellers left the house mostly furnished and stocked with supplies and a helpful "home instructions" booklet. One line of their "home instructions" stood out: "In the event of a power outage, there are flashlights and candles in the mudroom."

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One of the downsides of living in a heavily wooded area like the Green Mountain National Forest is that we're susceptible to the occasional power outage due to storms and downed wires. This is mainly a risk in Vermont's long winter months when the tree limbs are heavy with snow and ice, and a strong wind can bring them down atop power lines.

In May 2017, Green Mountain Power (our soon-to-be utility, also known as GMP) announced an innovative new partnership with Tesla. For $15 per month, we could add a new Tesla Powerwall 2 battery to our home.

In addition to backup power benefits, we would contribute to GMP's efforts to rely on distributed energy storage – instead of natural gas "peaker plants" – to meet spikes in electricity demand. We were determined to support the pilot program, which the New York Times described as "a bold experiment aimed at turning homes, neighborhoods and towns into virtual power plants, able to reduce the amount of energy they draw from the central electric system."

Given the resiliency benefits and positive environmental impact, $15 per month seemed great. As a point of comparison, buying and installing the Tesla Powerwall 2 outright would cost over $10,000. Leasing it from Green Mountain Power will cost us just $180 yearly, or $1,800 over the 10-year term. (We also could pay for the 10-year lease upfront at a slight discount of $1,500).

In early June, I contacted Green Mountain Power and asked if we could join their pilot program. A few hours later, I received this welcome email (below) and a verbal confirmation that we were one of the first several hundred customers enrolled in their 2,000-household pilot program.

This was the last communication I received from Green Mountain Power – all messages and calls from that point forward were with Tesla.

In early November 2017, about five months after receiving the welcome email from Green Mountain Power,­ I received an email from an Energy Advisor at Tesla. We scheduled a call to discuss the Powerwall 2 pilot program in more detail.

Tesla's Energy Advisors were based out of Las Vegas. They were my main point of contact for the scheduling process and were knowledgeable and fun to talk to. From what I could tell, they had a few goals:

  • Could you confirm whether I already had solar panels or planned to install them?

  • Verify that I understood the structure of the leasing arrangement with my utility (10 years at $15 per month)

  • Verify that I understood that Green Mountain Power could use the energy stored Powerwall during peak energy times, so long as we weren't relying on it.

Before signing the lease contract with Green Mountain Power, I had to take the Tesla Powerwall Self-Survey to identify the location of the requested battery installation, share photos of my electric panel, and discuss any unique electrical requirements (our hot tub is on a separate breaker, for example). The self-survey process required a smartphone and Internet connection, took about 30 minutes, and was intuitive and easy to complete. Everything was done remotely, though Tesla offered to send a representative if I requested it.

After emailing the self-survey back to Tesla's Energy Advisors, their engineers remotely designed a blueprint of the project. This design process took about three weeks from start to finish. Before I could schedule the installation date, Tesla sent me a contract and installation design to review via email.

In early January 2018, Tesla sent me the final leasing contract and installation project design. The most exciting part of the contract to me was the description of the utility's use of the energy from my soon-to-be battery:

After I signed the contract, Tesla's Energy Advisor reviewed it and then scheduled an installation date for the following month, February 2018.

The three-person team from Tesla Energy arrived at 10:00 am on a Friday in mid-February. All three were former SolarCity employees and had experience with solar panels and battery storage.

We walked the exterior and interior of the house after their arrival to identify the best location to install the Tesla Powerwall 2. The Tesla Powerwall 2 will technically perform better indoors due to less extreme temperature changes, but it can also be installed outside. Ideally, it would be installed within 20 feet of the electric meter, but further is possible. The battery should be placed outdoors in a more protected area if possible.

Tesla's remote design team in Las Vegas had initially thought an indoor installation was possible in our mudroom. Still, the onsite team didn't concur – they thought it would take up too much space and limit our mudroom's storage potential. I agreed with them, and we opted for an outdoor installation under the eave of our roof in a dry location with good sun exposure.

The installation process took about six hours, four of which had to have the power turned off. The newly installed battery can provide backup power for all our electric appliances under 30 Amp.

The Powerwall can't back up devices over 50 Amp (this is called a "partial home backup"). As a result, we had to move our electric stove and hot tub to a new electric panel on the house's exterior. The panel is between the electric meter and the battery so that the Tesla Powerwall can supply backup power to all of our critical appliances on the interior panel (electric baseboard heating, lighting, refrigerator, etc.) but will not attempt to power our stove or hot tub in a power outage.

As an added benefit, moving the stove and hot tub breakers to a new electric panel created additional space in our original electric panel for future electrical appliances. In our case, we’re planning to add an air source heat pump (ASHP) in the next few months. This new breaker space will allow the ASHP to be backed up by the Tesla Powerwall battery in cases of power outages, ensuring we have access to an energy-efficient heating source even in storms and blackouts.

Overall, I've been impressed with the responsiveness and professionalism of both Green Mountain Power and Tesla Energy, especially given that this is a pilot program for both of them, and our home was one of its first participants.

I'm pleased that Green Mountain Power is proactively ensuring we have access to reliable backup power in an emergency, all at the bargain price of $15 per month. I'm also optimistic about this pilot program. I hope it can serve as a model for larger utilities to study – particularly in parts of the U.S. where other homeowners are similarly worried about blackouts and grid reliability.

I've also been impressed with Tesla Energy's customer support, installation crew, and online and mobile technology use wherever possible (screenshots below). The Tesla mobile app allows us to monitor how charged our battery is and watch the power flow from the grid to our battery and Vermont cabin.

Tesla Energy's installers worked with me to free up space in my electric panel, setting us up for the installation of an ASHP down the road – all at no marginal cost to me and no real benefit to Tesla (as they don't yet sell air source heat pumps!). Overall, it was a great experience to work with both Green Mountain Power and Tesla Energy, and we're excited to be part of this new pilot program in Vermont.

Our Powerwall went into overdrive in the first week of July. Green Mountain Power was pulling power rapidly from its 500+ batteries across the state to meet surges in electricity demand. Here's what my energy usage report looked like on my Tesla app:

Even though I wasn't at the house most of the week, the app showed stored battery power being pulled back to the grid daily (see the green bars below the axis). You can see that they needed so much energy that my battery was completely drained by Sunday. They had to refill it again on Monday, then used much of it to meet spiking demand on Tuesday and Wednesday. GMP wrote a great article about this heat wave and explained that "during peak demand hours, this [virtual power plant] helped GMP offset approximately 17,600 pounds of carbon, the equivalent of not using about 910 gallons of gasoline."

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