(large image 34k .jpg) (huge image 130k .jpg) One advantage of microturbines is the ability to add capacity as needed. Systems can range from just one microturbine to an extended row of microturbines. As needs increase, new microturbines can be added. (Photo courtesy of Capstone Turbines.)

Great River tests microturbine as distributed power generator

By Carolyn Hinkley

As California continues to sort out its energy crisis, utilities across the nation are stepping up their efforts to examine alternative sources of power. Great River Energy's microturbine test program is one such example.

A 30-kW microturbine is located at Great River's Elk River Station near the company's headquarters in Elk River, Minn. It is one of nine being field tested in a program funded by the Cooperative Research Network, the Electric Power Research Institute, and the Department of Energy. Testing of the unit, which was manufactured by Capstone Turbine Corporation, began in April.

"Our intent is to gather data and get experience in using the equipment to see if we can work out the bugs before it is suitable for distributed applications," said Wayne Hanson, Minnesota Generation manager for Great River who is overseeing the testing.

"Our intent is to gather data and get experience... to see if we can work out the bugs before it is suitable for distributed applications."

Microturbines are popular power sources because they produce few emissions and require little maintenance. More importantly, microturbines are part of distributed generation systems that produce power at or near the site where it is consumed. Because these systems can be quickly and economically installed at customer sites where utility lines are already overloaded or non-existent, they have many distinct advantages.

For example, a 30-kW microturbine-which generates enough electricity to serve six homes or small businesses-could be installed at a local fast food restaurant, another small company or at a neighborhood clubhouse, limiting customer reliance on the bulk power grid. "It's big enough to run a small industry or if one isn't big enough, you could hook several together," Hanson said.

Such benefits are starting to catch on among Great River's 29 distribution cooperatives. "More and more of our customers are becoming interested in distributed generation, especially given the shortage of energy in California," said Therese LeCanne, external communications coordinator for Great River.

The downside to distributed generation is not yet known. Interconnection standards, safety and reliability, rate structures, buying and selling and parallel use with the bulk power grid are issues that still need to be addressed. However, microturbines have come a long way from their initial use in big industries like the automotive and aerospace fields. They have since evolved into smaller units with a few moving parts that can run on a variety of fuels, including propane, gasoline or natural gas.

Great River's unit is powered by natural gas and is the size of a large refrigerator. The testing, which lasts for two years, will evaluate the microturbine's performance, durability, reliability and maintenance. Every month, Great River will send test data regarding its operation to EPRI.

"We believe this technology shows promise and may well become a very important part of services our customers will want," said Hanson. "That is why we are taking a closer look so we have direct experience with this type of generating equipment if the need arises. My gut feeling is that the microturbine will be extremely reliable. While the present cost-about $30,000 per 30-kW unit-is too high, if the costs come down it could dramatically change the way we do business," Hanson said.

How a microturbine works Great River's Capstone microturbine operates by compressing incoming air with a single-stage compressor. The compressed air is forced into the cold side of the recuperator. The recuperator uses exhaust heat from the unit to preheat the incoming air before entering the combustion chamber. In the combustion chamber, the preheated air and natural gas are combined and ignited. The hot gases pass through the single-stage turbine where the heat energy is transferred to rotating energy. Electricity is produced from the DC generator attached to the shaft of the rotating turbine. The unit has an inverter that converts the generator's DC output to 60-cycle AC power. (Source: Great River Energy News)