Can Tesla's home battery lower your electric bill?
Tesla CEO Elon Musk has a plan to provide homes with energy storage, but it's less clear how long it will take for that move to benefit consumers. · CNBC

There's no doubt that Elon Musk's announcement that Tesla (Toronto Stock Exchange: TXL-CA) Motors will enter the energy-storage market last week excited Tesla fanboys and a good bit of the stock market. But are the economics compelling enough that consumers should get excited, too?

That's a less compelling proposition. In the same way that payback periods for hybrid cars and rooftop solar slowed early adoption, Tesla's bold utility-market move will take some time to prove its worth when it comes to your electricity bill.

Already enthusiasm for the product has been keen. Yesterday Musk announced that there had been 38,000 reservations for the power unit in California, a sellout into next year, but he also conceded that the system currently makes little economic sense for most utility customers in the U.S.

Tesla's $3,000 to $3,500 Powerwall system for homeowners (the price depends on the size of the system, either the 7-kWh or 10-kWh version) may actually cost as much as $9,000-including installation and ancillary electronics-for the consumer, said Dean Frankel, an analyst at Lux Research in New York.

"You'll likely see a price to the consumer of $7,000 to $9,000," Frankel said. "It depends on how cheaply Tesla's [installation] partners can get the power electronics."

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In places like California, where there are generous incentives for installing renewable power, a homeowner could save about $2 a day, meaning the system pays for itself in four to six years, said Mark Duvall, director of energy utilization at the Electric Power Research Institute, who's based in the northern California town of Half Moon Bay. In most of the rest of the country, the payoff would be longer because government incentives to go solar are smaller.

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Tesla (TSLA)'s system, which will become available this summer, is still about 50 percent cheaper than power-storage systems that have been on the market before, Duvall said. And for people who want the storage system as a way to provide emergency backup power-which is expected to be a small part of the demand-Tesla's units are cost-competitive, with backup generators that run on gasoline or natural gas.

But for most people, energy storage will have to get still cheaper, and there will need to be new mechanisms and business models to help spread out the cost before it makes both short-term and long-term financial sense.

Here's how to think about it.

Currently, the business model works great for Musk and his holdings.