Planning has begun on a new fuel cell power generation plant in Bridgeport that could become the world's largest.

The plant would consist of five 2-megawatt fuel cells that together would generate 10-megawatts of power, enough energy for nearly 10,000 homes.

Danbury-based FuelCell Energy would supply the fuel cells for the plant at a cost of about $30 million. Additional money would be needed to acquire the 2-acre industrial site on which the plant would be situated and to pay to install the fuel cells. The final cost of the project has not been determined.

Financing would come from private investors, but developers hope to qualify for a state program that would allow them to sell electricity through state utility companies at above-market rates.

The state's Clean Energy Fund has approved a loan of up to $500,000 for "pre-development" design work and planning on the project.

Lise Dondy, the fund's chief operating officer, said Tuesday that the fuel cell project would provide clean power, augment energy supplies in high-demand Fairfield County and promote economic development in the state's budding fuel cell industry.

"This is not just an energy project. It's also a very important economic development project," Dondy said.

James Murkett, principal at Farmington-based PurePower LLC, the project developer, said the fuel cell project hopes to participate in a state program aimed at developing 100 megawatts of power from clean energy sources in Connecticut by 2008.

To encourage that, the state has authorized participating electric utilities to pay a premium for the "clean" power of up to 5.5 cents a kilowatt hour above market rates and pass the cost on to customers.

Murkett said he hoped the Bridgeport fuel cell plant could be completed by next year. But first, the plant requires approval to participate in Project 100 and must also get the support of the state Department of Public Utility Control.

R. Daniel Brdar, president and chief executive of FuelCell Energy, said the project could help his company boost production volume and cut costs. Such a ramp-up in production has been a key goal for fuel cell companies in trying to achieve profitability.

In their simplest form, fuel cells act like giant batteries by combining oxygen and hydrogen to generate electricity while giving off only water vapor as a byproduct. Fuel cells made by FuelCell Energy extract the hydrogen from conventional fuels, such as natural gas.

The process is more efficient than combustion in gas turbine power plants, so more electricity can be generated from the same amount of fuel. And because the fuel is not burned, the plants don't give off harmful emissions.

But high production costs have so far hampered acceptance of the technology for commercial power generation.

The Long Island Power Authority last year announced plans for a 10-megawatt fuel cell project that it said would be the world's largest when completed.

But progress on the project has been stalled.