Friday, April 22, 2011

Can Solar & Smart Grid Speak the Same Language?

Too much solar power can be bad for the power grid, if utilities can’t monitor it and control it. The wild up-and-down swings that come from lots of little rooftops plastered with solar panels can become too much for some local grids to handle. When that happens, utilities have little choice but to shut them off.

So it would be nice if solar panels — or more specifically, the inverters that turn their direct current into grid-ready AC — could talk to the smart grid, to let utilities know what’s going on. This week, the utility industry released a common standard for doing just that. The next step will be for solar inverter makers and smart grid vendors to make equipment and software that speaks the language, and start testing it out. (To learn more about the intersection of smart grid and solar come to Green:Net on April 21 in San Francisco, where we’ll feature a discussion between NRG Energy CEO David Crane and Silver Spring Networks EVP & CMO Eric Dresselhuys.)

The new standard from the Distributed Network Protocol (DNP) Users Group is the result of nearly two years of effort by the industry, aimed at capturing some of the extra benefits that come from solar panels and inverters. Besides delivering power, inverters can manage voltage and reactive power fluctuations, and can push power to storage systems to cover the the passing of clouds over panels — or save up to feed back into the grid when it’s facing peak demand.

Indeed, projects that integrate these kinds of functions are underway around the world. Echelon is working with big inverter maker SMA Solar Technology and Fat Spaniel was bought by inverter maker Power-One. Enphase uses its own technology for its microinverters, as does Petra Solar with its pole-mounted, solar panel-connected microinverter arrays. Big players like General Electric, Siemens and Schneider Electric are also getting involved.

But without a standard to build to, they’ve all progressed along unique, mostly proprietary lines, said Brian Seal, analyst with the Electric Power Research Institute. In practice, that means a lot of the cool things inverters could do for the grid were left untouched, just because they were too hard for utilities to operate, he said. It took two years, but the industry has finally come up with a common language to get around that problem via DNP3, one of North America’s most common grid control standards, he said.

“This release is significant, because we now have a standard document that allows manufacturers to pick it up and actually build to it,” Seal said. While he didn’t name any companies that have announced technology around the new standard, he did note that the working group that came up with it had 450 individual participants, including every inverter maker he knows of. EPRI coordinated the effort with the Department of Energy, Sandia National Laboratories and the Solar Electric Power Association. For more information, read my GigaOm Pro report, EPRI’s Solar Power Phrasebook — a Guide to Future Communications (subscription required).

What’s next? Eventually, a world in which every inverter and smart grid device can plug into a standards-based system and open up the innate abilities — absorbing and releasing power to keep the grid in balance — to manipulation and control by any number of software platforms, Seal said. Of course, there’s a long way to go before that happens, and interoperability testing and field trials are next on the agenda.

What are the benefits? First and foremost: enable solar to continue to grow. While it’s hard to predict just how much local solar power it takes to destabilize the grid, Energy Secretary Steven Chu has said that the 20 percent wind power levels seen in the Pacific Northwest present problems with stability. Local neighborhoods aren’t likely to be able to take much more than that either.

Instability can even force utilities to stop new solar arrays from being built, or force them to hook up smart grid functions to do it. In Germany, where generous government subsidies have led to the world’s most solar panel-saturated neighborhoods, new medium-voltage grid codes require all solar inverters to provide a long list of advanced grid support features such as reactive power and VAR support, Seal noted.

While DNP3 is the main technology used for grid field equipment for the U.S. and Australia, Europe relies on a set of standards known as IEC 61850, and the two are working together, he said. Standards geeks will also be interested to hear that the IEEE 1547.8 group, which deals with distributed energy resources-to-grid integration, is also getting involved.


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