UCI scientists first to predict air quality impact of small-scale power sources

Technique could help regulators develop policies for distributed generation

As California searches for more sources of power, researchers at UC Irvine have created the first scientific method for predicting the impact of small-scale generators on air quality -- a tool that could help the state develop environmentally sound policies to regulate and promote their use.

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. Distributed generation -- the operation of many small stationary power generators located throughout an urban air basin -- includes fuel cells, photovoltaics, gas turbines, micro-turbine generators and natural gas internal combustion engines. The use of clean distributed generation in place of traditional power-plant generation 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.

Results showed that maximum levels of ozone and particulate matter could increase slightly in Southern California because of more distributed generation use, but the impact could be far less than other power-production alternatives, such as building more power plants inside the air basin. Officials throughout the United States are discussing the merits of using more distributed generation because existing 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. "Decision-makers 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."

This study by Dabdub; Scott Samuelsen, director of the National Fuel Cell Research Center at UCI; and Jack Brouwer, associate director of the center, is the first to determine the potential air quality impact of distributed generation. Some results were published online in the September issue of Atmospheric Environment.

The research team found that if distributed generation were used to meet up to 20 percent of the increased power demand in Southern California by 2010, the basin-wide peak ozone level would increase by no more than three parts per billion. In 2003, the maximum one-hour ozone level in the South Coast air basin was 194 parts per billion. Ozone can harm the upper respiratory tract, causing a cough, shortness of breath and nausea.

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, 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 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.

"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. This small-scale technology has the potential to fulfill the energy needs of many consumers and provide overall energy efficiency and cost savings."

Scientists used their computer model and research technique to determine when, where and how distributed generation could be used to produce the best possible air quality impact. They found that it is best to operate small-scale technologies as evenly as possible with regard to time, avoiding short bursts of operation. Distributed generation should be installed equally throughout the air basin, not concentrated in any one area, and the cleanest generation technologies such as fuel cell and photovoltaic devices should be used. These two technologies were found to have zero impact on ozone and particulate matter in the atmosphere -- even though fuel cell systems do produce emissions.

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 in place of a 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, researchers said. Their 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.

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This project was funded by the California Energy Commission under the Public Interest Energy Research program.

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