Last week we reported that SolarCity more than doubled its battery pack business with Tesla Energy in 2015 versus the previous year, and the trend is set to continue as the solar installer confirmed today that it selected Tesla’s energy division to supply its massive energy storage project on Kaua’i Island in Hawaii.

We reported on the project last year when SolarCity announced its power purchase agreement (PPA) with Kaua’i electric utility (KIUC) for two 12 MW solar arrays and their intention to install 52 MWh of energy storage.

At the time, SolarCity said it had yet to make a choice of supplier for the battery packs to be installed on the island, but everything was pointing toward Tesla due to their partnership and related parties – Tesla CEO Elon Musk is chairman of both companies.

This project could be one of the biggest to date for both companies in term of energy storage. The 52 MWh Kaua’i project requires 520 Powerpacks with each a capacity 100 kWh. As per the price of $250/kWh disclosed by Musk, it would represent a $13 million project. Though the $250/kWh figure was for the Powerpack in general, not especially for this project.

In a press release today, SolarCity describes the project:

The 52 MWh Tesla Powerpack lithium-ion battery storage system will feed up to 13 megawatts of electricity onto the grid to “shave” the amount of conventional power generation needed to meet peak demand in the evening from 5 p.m. to 10 p.m.

By using the solar energy stored in the battery instead of diesel generators, KIUC will reduce its use of imported fossil fuels and also cut its greenhouse gas emissions.

Under the terms of the 20-year contract announced in September 2015, KIUC will pay SolarCity 14.5 cents per kilowatt hour, only slightly more than the cost of energy from KIUC’s two existing 12 megawatt solar arrays, whose output is available only during the day.

The company says that the project has already received most of its required state and county approvals and is now awaiting approval by the Hawai’i Public Utilities Commission.

In the past, SolarCity had problems dealing with local electric utilities in Hawaii and when Tesla first announced its ‘Tesla Energy” line of energy storage products, the solar installer announced that it will use them to offer an option for home owners in Hawaii to go completely off-grid. The announcement came after SolarCity’s customers in Hawaii have reported difficulties connecting their PV systems to Hawaiian Electric Co.’s grid.

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