Rooftop Solar With Batteries Included

General Electric’s "net-zero energy" home of the future – which is planned for 2015, but exists only on paper right now – relies on a rooftop solar array to give the home enough energy to spin back the electricity meter (see GE Unveils Net Zero Energy Home Strategy).

But that blueprint also includes a battery. Without it, solar may betoo unstable an energy source to incorporate into utility grids in abig way.

Silent Power has a solarinverter-battery rig it says can accomplish that balancing task. Infact, the Baxter, Minn.-based startup is involved with GE in at least afew smart grid projects seeking stimulus funding to install thosesystems across a large number of homes, CEO Todd Headlee said last weekat the Clean Energy Venture Summit in Austin, Texas.

Silent Power has raised $4 million in angel financing, and isseeking to raise a $7 million series A round to "attack the utilityspace," with commercialization planned for 2011, Headlee said.

As for GE, "We’ve partnered with them on a couple of proposals," hesaid, though he wouldn’t give additional details on the projects thetwo were planning (see Green Light post). 

The problem with utility-scale energy storage has so far been itsprice. Beyond huge, capital-intensive and site-limited systems likepumped hydro and compressed air energy storage, batteries, flywheels,fuel cells and other distributed energy storage technologies are stilltoo expensive for most utilities to justify (see Grid Energy Storage: Big Market, Tough to Tackle).

Silent Energy says it can drastically undercut those costs by maxingout the federal tax rebate available for solar system installations –and getting utilities to foot part of the remaining bill.

A Silent Power system should add about $5,000 to the cost of atypical solar installation, Headlee said. The 30-percent federal taxcredit shaves that by 30 percent, leaving about $3,500 remaining – or,as Silent Power likes to frame it, about $350 per kilowatt-hour instorage capacity. That’s cheaper than commercially available batterystorage system today, though it’s a target price for many.

Batteries count for the solar credit when linked to an inverter system, Headlee said. If Congress passes a bill proposed by Sen. Ron Wyden(D.-Ore.) that offers an energy storage equivalent tax incentives towind and solar, that could open up the pool of financial support, hesaid (see Energy Bill Could Boost Storage Technologies).

Granted, the batteries won’t last more than a few hours, he said.But that’s enough for utilities to smooth the difference between thetime that solar panels get their best output, in the mid-afternoon, andthe slightly later peak demand times that are typical for utilitiesduring hot summer afternoons as people get home from work and startturning stuff on, he said.

That demand response capacity could be worth something to utilities– perhaps, even a $3,500 rebate or incentive to homeowners to makeSilent Power’s system as cheap as a regular solar panel array, hesuggested.

A solar-battery system would require inverter systems that canswitch instantly between the two – something Silent Power’s system cando, Headlee said. About 200 homes with Silent Power’s units should givea utility 1 megawatt of load-shifting capacity, he estimated.

Beyond that, batteries can help smooth the big swings in solar panelgeneration when clouds pass overhead, he said. Spread out toneighborhood scale, such drastic ups and downs in home power demandcould spell trouble for an unprepared distribution grid.

The market is huge, Headlee said. American Electric Power, for one,says it will need 1 gigawatt of storage, or 2.6 percent of generationcapacity, by 2020, he noted, and California may require 4 gigawatts ofstorage to reach its goal of getting a third of its power fromrenewable resources by 2020. About 20 gigawatts of new storage wouldrepresent a $10 billion market, he said (see Green Light post).

Beyond its work with GE, Silent Power has been talking with California utilities including San Diego Gas & Electric, Southern California Edison and Sacramento Municipal Utility District, he said.

Most of California’s utilities are asking the DOE for money to buildgrid storage, but those projects have concentrated on larger-scalestorage, like a 30-megawatt lithium-ion battery Southern CaliforniaEdison wants A123 Systems to build, or Pacific Gas & Electric‘s plan for a compressed air energy storage system (see PG&E Wants DOE Dollars for Underground Air Energy Storage and SoCal Edison Wants A123’s Biggest Grid Battery Ever).

But SDG&E’s proposed $212 million microgrid project,which is also seeking DOE stimulus funding, is likely to requiresmaller distributed energy storage systems, Headlee noted (see Balance Energy Wants to Build Microgrids, Starting With San Diego).

For now, the company plans to use lead-acid batteries with anestimated five to seven year lifespan, he said. But it’s looking intolithium-ion and advanced lead-acid batteries as well, he said.

A few venture capitalists briefed on Silent Power’s plans at lastweek’s conference in Austin noted that the company might be a bit earlyto the market. Systems for allowing utilities to control large numbersof home-based batteries are in their infancy, though the millions ofsmart meters being deployed could help extend those networks, Headleesaid.

In fact, smart grid startup GridPoint started out in 2003 with asimilar business plan, then switched to software after finding themarket too small, he said (see GridPoint Gets $120M, Buys V2Green).

But then, utilities have been running demand response programs foryears, with factories and other large power users turning down theiruse at peak demand times, Headlee said (see Is Demand Response Doomed?)

And utilities expecting hundreds of megawatts of rooftop solarpanels to be installed in their service territories may feel under thegun to put storage in place to make it an asset, rather than agrid-destabilizing liability, he said.

Interact with smart grid industry visionaries fromNorth American utilities, innovative hardware and software vendors andleading industry consortiums at The Networked Grid on November 4 in San Francisco.




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