Will Solar Crash the Smart Grid?

THE STORAGE SOLUTION

At San Diego Gas & Electric, "Storage is absolutely part of the solution," Baker said, all the way down to batteries at customer premises.

To the north, utility Southern California Edison is asking DOE for $35 million to fund a $70 million smart grid project in Irvine, Calif. that will include household batteries linked to solar panels.

General Electric, a project partner, has said it will bring "net-zero energy homes" to market by 2015, with a concept diagram that includes basement batteries to store rooftop solar power (see GE Unveils Net Zero Energy Home Strategy).

In fact, much of today's rooftop PV comes with small batteries to cushion household wiring from the panels' ups and downs in power delivery. That's according to Michael Ozog, COO of smart grid products at Integral Analytics, which is working on integrating such household systems for utilities including Duke Energy (see Integral Analytics: Orchestrating Duke's 'Virtual Power Plant').

Utilities such as the Sacramento Municipal Utility District are looking at ways to control existing PV systems, he added. The problem is that most systems out there today weren't made to be controlled by, say, a smart meter calling for a battery to discharge power to meet a utility's peak demand – something Integral Analytics has found out in field trials, he said.

More smart grid-ready systems involving new batteries and inverter technologies would be useful, he said (see Rooftop Solar, Batteries Included). But they could add too much to the already daunting costs of a home solar system for most customers, he said.

"I think you'll have to have some storage someplace else to manage that volatility," he said – and if utility customers won't buy it, the utility may have to.

Some utilities are looking at cargo container-sized flow batteries or sodium-sulfur batteries at substations (see Grid Energy Storage: Big Market, Tough to Tackle). Other utilities are considering a similar, small-scale distributed approach known as community energy storage, Cazalet noted (see Utility to Try Backyard Storage).

"That's where you put a battery on a box next to the transformer on the pole, and the benefit for them is, they can put that into the distribution rate base," he explained. "It could help some of the distribution problems caused by PV, and changing loads from charging plug-in vehicles." IDC analyst Nadav Enbar and now Nissan have floated the idea of using aged lithium-ion battery packs from cars for utility storage.

"But if you put that same battery in the home, you're going to have to finance that yourself," Cazelet said. "And if you're providing benefits to the grid, are you going to be compensated for that?"

BALANCING THE GRID

Maybe utilities could balance growing amounts of rooftop solar power without a lot of expensive batteries.

Inverters, which convert solar panel DC output into grid-ready AC, could help by delivering short bursts of energy, EPRI's Wakefield said.

That could give them a role in niche utility power needs such as frequency regulation, or the task of keeping the grid humming at 60 hertz, which now takes up about 1.5 percent of the nation's generating capacity.

Inverter companies such as Satcon and Petra Solar have discussed using their products for these kind of grid-balancing tasks. Inverters could also help with voltage regulation and VAR, or reactive power, problems, Wakefield said. Those can sap distribution grids of some 5 percent of their efficiency (see Notes From a National Smart Grid Experiment).

"The inverters have the technology to do it," Wakefield said. Unfortunately, "There are some functions we just cannot do, because the standards development isn't in place."

Specifically, the IEEE 1547 standards for linking distributed power to the grid don't support inverters for voltage regulation and VAR support, though proposals are in works to include them, he said. Also, many inverters use unique communications that would be easier to integrate into smart grid systems if they were standardized, he said.

There's another form of balancing that can be done by subtracting, rather than adding, power to the grid – demand response, or the ability for utilities to turn down customer's power use when they're facing peak loads on the system.

Demand response tends to be a centralized affair at present, with utility dispatchers paying agreeable customers and giving them ample advance warning to turn down their big power loads – sometimes via radio signals, text messages, emails or  phone calls – when needed.

But automated systems running over smart meter communications networks could open up new ways to tap the demand response potential in the home – imagine turning down the air conditioner when the solar panels detect a cloud passing overhead.

Tendril Networks, which makes gear and software to manage household energy use, and Fat Spaniel Technologies, which monitors solar panel output, announced a partnership to try just that. Some of Tendril's 30 or so utility pilot project partners have been asking for such technology, CEO Adrian Tuck said last week (see Tendril Wants to Link to Solar Panels).

Of course, utilities that can predict when solar panels are about to fade could fire up peaker plants or dip into demand response capacity to match it. That's where microclimate forecasting comes in, EPRI's Wakefield said.

Every utility forecasts the weather as a part of their day-to-day business. It's hard to miss a heat wave's effect on air conditioning loads. Pinpointing local weather conditions in real time – and then adjusting the local grid in response – is a more complicated matter.

Given the complications, projects to integrate solar panels, storage and smart grid systems are more easily contemplated in smaller units. A host of startups are looking to provide the intelligence to do that, as well as find ways to make the more controllable power pay off by selling into various markets.

Well-funded smart grid software startup GridPoint is helping Xcel Energy manage rooftop solar for Boulder, Colo. residents in its SmartGridCity project. Duke Energy has enlisted Integral Analytics to manage solar, storage and demand response for about 500 customers on its McAlpine substation in its headquarters city of Charlotte, N.C.

Fort Collins, Colo.'s FortZED (Zero Energy District) project has enlisted hometown company Spirae to help (see Green Light post), and Viridity Energy has partnered with Siemens to use $1.2 million of utility PECO Energy's $200 million DOE smart grid grant to set up a microgrid project at Pittsburgh's Drexel University.

San Diego Gas & Electric is using the town of Borrego Springs as such a test bed, and has asked for DOE grants to connect it to a second such "microgrid" at the University of California at San Diego, Baker said (see Microgrids: $2.1B Market By 2015).

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