MONTPELIER (AP) >> The state's largest electric utility is getting ready to offer customers in-home batteries made by Tesla, best known for making electric cars.

In a letter Thursday to the Public Service Board, Green Mountain Power said it would become the first U.S. utility to offer the Tesla Powerwall.

The wall-mounted lithium-ion battery, designed to store electricity for residential customers, is just over 4 feet tall, almost 3 feet wide and 7 inches thick. Each costs about $6,500.

Being able to store electricity made from solar panels and other renewable, but intermittent, power sources is seen as a key challenge in the push for renewable energy.

The Tesla batteries will not be enough on their own to allow a typical residential customer to live completely off the grid. But they will store enough power to ensure customers can keep at least some of their lights on and provide power for things like heating systems during a power outage.

When paired with rooftop solar panels, the batteries can store electricity that can be used when the sun is not shining. The batteries also can be used by customers who do not have solar panels. Those units would be charged by electricity from the grid.

Customers who get the batteries can choose to share the power with the utility during times of high demand. Green Mountain Power plans to offer three options to customers:


• Customers can pay about $37.50 a month and share stored power with the utility.

• Customers who buy the battery and share stored energy with GMP will receive a monthly credit of $31.76.

• Customers can buy the battery outright and not share the power.

The first 10 Tesla batteries will be installed in the Rutland region. After that, the utility plans to offer them to about 500 customers.