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by Jeff St. John
April 13, 2016

It was just about a year ago that Tesla unveiled its Powerwall -- a sleek, capsule-like lithium-ion battery system, available in 7- and 10-kilowatt-hour configurations meant to provide backup power or optimize the value of rooftop solar PV. CEO Elon Musk said the product could “fundamentally change the way the world uses energy at the extreme scale."

The public reaction was huge, with Musk noting during an earnings call the week after launch that preorders had risen to some 38,000 -- although that’s without a money-down requirement, unlike...