Richard C. Oliver is encouraging green-energy production by paying about $5 to $6 more a month on his utility bill.

That's the difference between what Rappahannock Electric Cooperative charges the Orange County farmer for electricity produced in the traditional way and the price for power generated using renewable resources such as biomass.

"It's a fairly small amount to pay to encourage people to generate renewables and stay in business and keep things going," said Oliver, who is chairman of REC's board of directors.

REC began offering members the opportunity to purchase green-energy certificates in June of 2008 at the urging of a few people attending the board's annual meetings for the past couple of years, he said.

Dominion Virginia Power began offering a similar option in January. Northern Virginia and Northern Neck electric cooperatives, the other electricity providers in the Fredericksburg area, aren't selling green-energy certificates yet, but are considering doing so.

REC's and Dominion's programs work like this: The utilities use the extra money to purchase certificates for renewable energy on a consumer's behalf. The certificates are guarantees that renewable energy was produced and delivered to the regional power grid.

The voluntary program also "encourages the development of new renewable power facilities, and reduces the environmental impact of generating electricity from fossil fuels," said Paul D. Koonce, Dominion Virginia Power's CEO, in a prepared statement.

According to EPA guidelines for calculating the environmental benefit, a utility that buys 1 megawatt of renewable energy prevents 18,828 pounds of carbon dioxide emissions.

REC members can purchase certificates for 100-kilowatt-hour blocks of green energy each month for 45 cents each, and there is no limit to the number they can buy. They have the option of making a one-time purchase or arranging to buy a set number of certificates each month for 12 months.

At Dominion, the fee for what it calls renewable-energy credits is a penny and a half per kilowatt-hour. Customers who sign up for Dominion's Green Energy program can buy as many blocks of 133 kilowatt-hours of renewable energy as they want for $2 each, or enroll in the 100 percent option, which buys renewable-energy certificates equal to their monthly electricity use.