Tesla's SolarCity subsidiary today announced it has converted the entire island of Ta'u in American Samoa to solar power through a massive microgrid project.

Ta'u, a 17-square-mile island and the most populous of the Manu'a Group of atolls, is located more than 4,000 miles from the U.S. West Coast. The island, which has about 785 residents, had been powered by diesel generators and struggled with regular power rationing and outages, SolarCity CTO Peter Rive stated in a blog about the project.

Tesla/SolarCity An aerial view of the Powerpack substation.

Each of Ta'u's generators used 300 gallons of diesel fuel a day or about 109,000 gallons per year.

Ta'u now hosts a solar farm with 5,328 photovoltaic panels and a storage plant made up of 60 Tesla lithium-ion battery Powerpacks that can store up to 6 megawatt hours-worth of electricity - enough to power the island for three days without sunlight. The battery plant can recharge with seven hours of daylight.

"I recall a time they weren't able to get the boat out here for two months," Keith Ahsoon, a Ta'u resident whose family owns one of the food stores on the island, was quoted as saying in Rive's blog. "We rely on that boat for everything, including importing diesel for the generators for all of our electricity. Once diesel gets low, we try to save it by using it only for mornings and afternoons."

Tesla Telsa's 60 Powerpacks can be recharged with seven hours of sunlight and power the island for three days.

The project was funded by the American Samoa Economic Development Authority, the U.S. Environmental Protection Agency and the Department of the Interior.

The system is expected to offset the use of more than 109,500 gallons of diesel per year.

"Factoring in the escalating cost of fuel, along with transporting such mass quantities to the small island, the financial impact is substantial," Rive wrote.

Tesla/SolarCity An aerial view of the photovoltaic solar power farm on Ta'u.

Tesla and SolarCity have been building microgrids on U.S. islands and in major cities for the past year or so.

Prior to the merger earlier this week, the two companies won a 20-year contract to build and run a 52 megawatt (mW) first-of-its-kind solar array and energy storage system on 50 acres for Hawaii's Kaua'i Island Utility Cooperative (KIUC).

Tesla/SolarCity Tesla and SolarCity won a 20-year contract to build and run a 52 megawatt solar array and energy storage system on 50 acres for Hawaii's Kaua'i Island Utility Cooperative.

Tesla supplied the batteries that will provide 13mW worth of capacity. SolarCity's solar array is expected to go live by the end of 2016.

The KIUC will purchase energy for 14.5 cents/kWh through a 20-year power purchase agreement.

Tesla was also selected in September to develop a Powerpack system providing 20 megawatts of capacity and 80 megawatt hours of generating power at the Southern California Edison Mira Loma substation, making it the largest lithium-ion battery storage project in the world.

Also in September, Tesla won a bid to build the largest lithium-ion battery storage plant in the world for the Southern California Edison Mira Loma Power Substation. The battery plant can hold 20MW of electricity and provide 80 megawatt hours of power.