Want a solar home? Consider batteries.

Most solar homes are still dependent on the grid, so when the grid fails, they lose power. But that's beginning to change as the solar industry begins to focus on battery storage as the next 'green' frontier.

Michaela Rehle/Reuters/File
Workers install solar panels on the roof of a farmstead barn in Binsham near Landshut, Germany, last year. Currently, most solar homes don't have onsite energy storage. Typically, adding backup batteries to a solar home adds about 30 percent to the cost.

When superstorm Sandy barreled into Long Island last October, it flooded Raina Brett Russo's home.

"Basically, the ocean and the bay came together in my living room," Ms. Russo says. "It hit us really hard."

The basement and first floor were underwater, three cars were flooded, and to the amazement of her neighbors, the power did not come back on any sooner than theirs. With 10.4 kilowatts' worth of solar panels bolted to her roof and undamaged, shouldn't the Russo house have been an oasis of light and power?

Not quite. Like most solar installations today, Russo's panels are connected to, and reliant on, the broader energy infrastructure. When the grid fails, most residential solar panels also fail. But that's beginning to change. The next evolution of home solar will be not in the panels that create energy, experts say, but in the batteries that can store it.

"Storage to me is the holy grail of renewable technology," says Dan Juhl, head of Juhl Energy, a Minnesota-based clean-energy company that offers, among other things, a hybrid solar-storage system called SolarBank. "With solar and wind we can produce power – no ifs, ands, or buts about it. And with a little storage, you're good to go."

The technology exists, but it comes at a price. Depending on a house's size, location, and consumption, storage adds about 30 percent to the cost of a solar installation, which averages $26,000. Also, batteries need to be replaced every six to 12 years, depending on whether they're used to provide energy at night or strictly as backup systems.

Some of that cost may be offset by the savings from buying less power from a central utility. Then there's the benefit of having working lights, refrigeration, and a charged cellphone in the aftermath of a storm, say supporters of solar power. Still, battery storage will have to come down in price to be competitive with conventional backup generators.

Solar panels themselves were once considered cost-prohibitive. Those prices have since plummeted, thanks to technological advances and a rapidly growing global market. The same could happen for storage.

"Ten or 15 years ago the battery was an afterthought because the photovoltaic module was the new, exciting technology," says Dean Middleton, director of sales for renewable energy at California-based Trojan Battery Company. "Today, there's much more of a focus on the battery."

Energy storage topped the list of high-demand features in a December 2012 global survey of 400 solar in-stallers, system integrators, and wholesalers by IHS Inc., a Colorado-based business analysis firm.

One-third of respondents said they expect to use energy storage in more than 40 percent of the photovoltaic systems they install by 2015. "Energy storage is becoming an increasingly important feature for PV systems, and if suppliers are able to deliver products in line with the industry's expectations, the market for energy storage in PV could increase significantly over the next two years," says Sam Wilkinson, a manager at IHS, in a release.

The nascent market is getting a boost from the US government. In November, the Department of Energy awarded $120 million to Argonne National Laboratory in suburban Chicago to lead research into better and cheaper batteries for vehicles and the electrical grid.

In the meantime, lead-acid batteries will do the trick. The technology is time-tested and well understood, unlike newer and more volatile storage systems. Batterymakers say that storage of lead-acid batteries, despite their ominous name, is clean, safe, and highly recyclable.

When combined with solar panels and a special inverter to direct the flow of energy to and from the various sources, the batteries offer a kind of energy security not available in most solar panel systems.

"While everybody is arguing about a smart grid and how it's going to work, anyone who installs this kind of system already has a smart grid right there in their home," says Mark Cerasuolo, senior marketing manager at OutBack Power Technologies in Arlington, Wash., which specializes in power conversion equipment. "Everything on your side of the meter is what really counts."

Four months passed before Russo and her family could move back into their storm-battered home. She is adamant about acquiring backup power for when the next storm comes. But Russo, cofounder of educational website EcoOutfitters.net, which is dedicated to demystifying the process of installing renewable energy systems, eschews conventional generators because of their emissions.

"Since we already have this solar system, let's use it as a backup," she says.

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