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Machine Design

A chicken in every pot, a generator in every backyard

September 27, 2001

Distributed generation is one of the ideas being batted around as a solution to energy problems. Promoters envision the day when small local generators, though primarily used for backup, also will be an integral part of the nation's power system. This scheme will be particularly useful, it is said, as utilities start charging more for power used during periods of peak demand. Backup generators will not only handle outages but also will be able to pump any excess generated power back into the grid. Even homeowners will be able to get into the act selling power back to the utility from sources such as windmills and solar cells.

Do such scenarios make sense? An interesting perspective on the question comes from Joe Koepfinger, a vice chair of the IEEE Working Group now defining a standard for connecting distributed generators to the electric grid. Koepfinger is installing a 20-kW generator in his backyard, but not out of an aspiration to sell juice back to the local utility. "Right now my house has been without power for three hours though the sun is shining," he recently explained from a cell phone. "I'm stuck at the end of four circuits."

Just retired after a 51-year career in the electric power industry, Koepfinger knows a thing or two about generators and the grid. That's why he maintains, "I could never recoup my costs if I tried to sell power back to the utility. I don't really see the advantage of connecting a small generator to the grid for the average homeowner."

The concept is more valid, he thinks, for businesses such as dot-coms that need power 24/7 where the penalty for interruptions may be severe. But numerous issues need resolution before power lines can handle connections from large numbers of kilowatt-sized generators.

One point concerns the potential for overloads. Electric lines for residences and small businesses all tap off a large transformer at a local substation. Sending power back to this distribution transformer from one small generator is no big deal, says Koepfinger, but "Nobody knows the size and number of these generators a given substation can sustain. It's a contentious issue that comes up repeatedly. The technology to figure this out is very sophisticated, and it's costly to do the necessary studies."

Even if technological questions are resolved, getting utilities to agree on a national standard might be problematical, Koepfinger thinks. The document his Working Group is now trying to hammer out stops short of the loading controversy. It treats only the first step toward distributed generation: Defining a standard electrical interface to the power line.

It's tough to get agreement even on that level. "Safety is the main issue. The problem is showing that the generator can separate itself adequately from the line and not try to carry some of the utility load," says Koepfinger. "Doing that to the satisfaction of all concerned parties is difficult."

The Working Group's initial concept for an interface took the form of a box on the side of a house analogous to that for phone service. Homeowners could plug in anything built to the standard. As discussions progressed, suppliers such as fuel cell makers argued it was more cost-effective to build the needed controls into their products rather than fabricate them separately. "This is one of the contested issues," says Koepfinger. "Whether or not you can build the interface into a generator and still get it accepted."

All 200 people on Koepfinger's Working Group have taken their shots at an initial draft standard. Members are in the process of resolving the issues that emerged. The revised document is due out for recirculation by the end of the year. If more problems arise, says Koepfinger, "All bets are off as far a projected release date."

Leland E. Teschler

TAGS: Technologies
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