By Bruce Brown

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As the summer heat wave drags on, nearly 500 Vermont homes with Tesla Powerwall batteries are staying cool,
. The state’s Green Mountain Power (GMP) electric company stored-solar-power project is paying off for the utility company and its customers.GMP launched the Powerwall program in 2015. The goal is to install the energy storage devices in 2,000 homes,
. Residential Powerwall installations started slowly, with approximately 220 installed by April, GMP told Electrek
. GMP also noted in April that thedemandfor Powerwalls was building, with 1,200 homeowners interested in the heavily subsidized units.Normally it costs about $7,000 for a
installation. GMP subsidizes the program with two options. Customers can pay $15 a month or a $1,500 one-time charge. The huge discounts work for GMP, however. Part of the deal is that customers allow GMP to treat the Powerwall units as “virtual power plants” to access stored energy for the grid.The current installed base also means GMP has potential 5,000 kWh of stored energy to access during periods of peak demand.The residential Powerwalls are charged by homeowners’ on solar panel arrays or by conventional power loaded when demand is low. According to Green Mountain Power, the utilities conventional power sources are 90 percent carbon-free — so any argument that the company burns dirty fuel to charge the batteries is not valid.GMP’s “green power” sources include solar farms, wind power, hydroelectric plants, and cow manure. The Cow Power program currently consists of 14 farms with approximately 13,500 cows. By burning themethane waste from cows, GMP cuts carbon emissions and produces power. The program powers 3,200 Vermont homes with the equivalent of 8.2 million gallons of gasoline by burning 73,000 tons of methane each year.With almost 500 Powerwalls in Vermont homes, the comfort and safety factors of backup power during the prolonged summer heat, it’s a good bet GMP customers will sign up for the remaining units.“We know our customers are environmentally conscious and make smart choices about their energy use every day. In this heat wave, our customers’ safety and comfort is key. We are so glad to be able to leverage innovation like battery storage to bring down costs for customers and keep them comfortable and safe,” Josh Castonguay, vice president and chief innovation officer at GMP, said in a statement. “Our growing network of stored energy is allowing us to use technology, in partnership with our customers, to deliver innovative solutions today.”

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