New Technique Pegs Air Impact of Small Power Sources

IRVINE, California, August 21, 2006 (ENS) - As California seeks more sources of clean electric power, researchers at University of California-Irvine have created the first scientific method for predicting the impact on air quality of small-scale generators located close to power users.

The operation of many small stationary power generators located throughout an urban air basin is called distributed generation. Power sources include fuel cells, solar photovoltaics, gas turbines, micro-turbine generators and natural gas internal combustion engines.

Officials throughout the United States are discussing the merits of using more distributed generation because existing power plants are reaching capacity at a time when power demand is increasing nationwide.

“Because of grid constraints, growing power demands and high power cost, California could become one of the first places where small-scale power production methods become widespread,” said Donald Dabdub, a professor of mechanical and environmental engineering in The Henry Samueli School of Engineering at the University of California-Irvine, UCI.

“Decisionmakers will need a way to assess distributed generation’s impact on air quality, and our computer model and methodology are the first to address this need,” Dabdub said.

Using a supercomputer, scientists analyzed thousands of variables including land-use information, emissions data and atmospheric chemistry to determine the potential effect of distributed generation on Southern California air by 2010.

Microturbines are small engines attached to high-speed electrical generators which can be powered by natural gas or biofuels. They provide a reliable source of electricity and heat for commercial businesses and industries. (Photo courtesy Capstone Turbine Corporation)

The use of clean distributed generation in place of traditional power plants cuts down on electricity transmission losses, reduces the need for unsightly overhead power lines and facilitates the use of generator waste heat, which further reduces electricity needs and emissions.

This study by Dabdub and Director of the National Fuel Cell Research Center at UCI Scott Samuelsen, with Jack Brouwer, associate director of the center, is the first to determine the potential air quality impact of distributed generation.

Donald Dabdub and Jack Brouwer are two of the researchers on the distributed generation research project. (Photo courtesy UCI)

In 2003, the maximum one-hour ozone level in the South Coast air basin was 194 parts per billion.

The peak concentration of particulate matter – small specks of chemicals and soot that can lodge in the lungs and cause health problems – would increase by no more than two micrograms per cubic meter.

In 2003, the peak daily particulate matter concentration in the South Coast air basin was 121 micrograms per cubic meter.

Despite the potential increases in ozone and particulate matter, the researchers say that appropriate use of distributed generation is better for the air than other methods of generating additional power such as building more nuclear, coal-fired or natural gas power plants.

“The use of distributed generation in Southern California is preferable to other in-basin strategies that we may be forced to adopt to meet the power demand in the future,” Brouwer said.

“Even the cleanest natural gas power plant will have a larger air quality impact than fuel cell distributed generation, said Brouwer. "This small-scale technology has the potential to fulfill the energy needs of many consumers and provide overall energy efficiency and cost savings.”

The scientists found that it is best to operate small-scale technologies as evenly as possible over time, avoiding short bursts of operation.

A General Motors stationary fuel cell unit generating power for an industrial process. (Photo courtesy GM)

A fuel cell works by converting the chemical energy of a fuel, such as natural gas, and an oxidant, such as air, directly to electricity using electro-chemistry. Solar photovoltaic devices use semiconducting materials to convert sunlight directly to electricity.

If fuel cells alone were used instead of the mixture of distributed generation technology investigated by the research team, they could lead to a reduction of up to three parts per billion in peak ozone and up to two micrograms per cubic meter of peak particulate matter, the researchers said.

The findings suggest that fuel cell distributed generation could reduce future peak ozone concentrations by as much as six parts per billion and peak particulate matter by up to three micrograms per cubic meter compared to current power plant technology.

The popularity of distributed generation is growing. Today, more than 2,000 megawatts of distributed generation facilities have been installed in California, and officials expect the addition of up to 400 megawatts in small-scale projects each year. About 60 gigawatts of installed capacity currently exist in California.

This project was funded by the California Energy Commission under the Public Interest Energy Research program. Some results were published online in the September issue of the journal "Atmospheric Environment."