pg_15 Battery Storage News.pdf

Tesla, Inc. began development of their Powerwall in 2012, and started production of their first generation version in 2015. Since then, they have developed the Powerwall 2, with increased capacity, and an option for a built-in inverter. The batteries are made of lithium ion, and are designed to “provide energy storage for solar self-consumption, load shifting and backup power” – Tesla. The first generation was rated at 6.4 kWh, with a 3.3 kW peak and continuous power output, while the Powerwall 2 is rated at 13.5 kWh with a peak power of 7kW, and a continuous power output of 5kW. The cost of the Powerwall 2 is listed at $6,200 on Tesla’s web site (includes battery and supporting hardware). The web site also estimates installation costs ranging from $800 to $2,000 (plus tax and permit fees). Tesla also produces the Powerpack, a battery for commercial applications; the Powerpack 2 has a capacity of 200 kWh.

GEO recently learned of two Ohio households who have deployed Tesla Powerwalls along with their solar arrays from Icon Solar, the installer. Eager to hear of their experience, GEO contacted the Rifes and Brookses to learn more.

The Brooks family resides in Southwest Ohio in Dayton Power & Light’s service territory. In August of 2016, they installed 24 Quartech Canadian Solar panels rated at 270 Watts each for a total array capacity of 6.48 kW on their home. To accompany their solar array they installed a first generation Tesla Powerwall. The unit is wall mounted in their garage and the system is grid connected. The Brookses’ primary goal in installing a Powerwall was to have the ability to have power even during a utility blackout. They were drawn to the Powerwall specifically for the back-up storage because the lithium ion battery in the Powerwall appeared a cleaner and more efficient option than lead batteries. The family found the installation costs of the Powerwall on par with estimates.

So far, the unit has performed up to the family’s expectations, but has only been used for one utility blackout. The battery also constantly charges and discharges from 50% capacity. So, every time it gets fully charged it will discharge power for consumption until 50% capacity before recharging. Since August, the Brookses’ array has produced 3.46 MWh, with 2.08 MWh consumed. They experienced two months with no electric bill, and have never paid more than $45 a month since installing solar.

Tesla Powerwall battery (right) with inverter, solar meter and main electrical box in basement of Rife solar home.

Tesla Powerwall battery (right) with inverter, solar meter and main electrical box in basement of Rife solar home.

The Rifes installed a 32 panel solar array rated at 8.64 kW on their home in rural Central Ohio in October of 2016, and a wall mounted first generation Powerwall in their basement. While investigating the thought of going solar, the Rifes knew they wanted a back-up power source given their rural location, a sump pump in their basement, and the threats posed from lengthy grid outages. While they knew nothing initially about the Powerwall, they were soon comparing the advantages of battery back-up power to that of a gas generator. When comparing the 30% tax credit applicable to the Powerwall and solar array system, the Powerwall proved more economic.

Since October of last year, the Rifes have used their Powerwall as a back-up power source twice when the grid went down. While most of their local area was out of power, including neighbors, the nearest gas station, and other local businesses, the Rife’s were able to heat and light their home and enjoy a little entertainment from the television! Their system is also set up to pull power from the Powerwall in the event that the solar array is not meeting all of their demand. In this case, up to 50% of the capacity can be discharged instead of pulling power from the grid. The remaining 50% is reserved for grid outages.

The Rifes estimate that their solar array will pay for itself in eight years (not including the cost of the Powerwall). Savings were immediately realized during November 2016, when the household received an electric bill of only $20, while the previous month’s bill was around $120 (before the solar was installed). Their system is also tied to a smart phone app, where they can monitor their usage, the array’s production, and battery levels.

-Emily Sautter-Goerig, Program Manager