PROVIDENCE — The developer of a planned solar-energy farm in Coventry said yesterday that the project can go forward only if the state passes legislation that makes renewable energy projects more financially attractive to developers.

Allco Renewable Energy, of New York, said its plan to build a 90-acre, 8-megawatt solar farm in western Coventry is contingent upon passage of legislation that assures that the developer will be able to sell its electricity at a certain price through a long-term contract.

At the State House yesterday, Allco executives spoke in favor of one such bill, the Rhode Island Renewable Energy Sources Act, introduced by Rep. Raymond J. Sullivan, D-Coventry.

That bill would require dominant electricity and gas utility National Grid to enter into contracts for at least 20 years to buy the electricity generated by renewable energy sources in Rhode Island, such as solar and wind projects.

The bill also sets the rates that National Grid would have to pay. Those rates, in some cases, are many times the rate the power distribution company now pays for electricity.

The House Corporations Committee took testimony on the Sullivan bill at a hearing yesterday. National Grid said the legislation would be too costly to ratepayers, and is opposing the bill.

“We agree with the spirit of the bill,” said Francis X. McMahon, president of Advocacy Solutions, who came to represent National Grid at the hearing. “But the costs would be extravagant to ratepayers.”

The General Assembly is considering several bills that seek to encourage the development of renewable energy projects.

For example, a bill introduced earlier this month by Senate President Joseph Montalbano, D-North Providence, would require National Grid to enter into “commercially reasonable” long-term contracts to buy renewable energy from developers that plan to build large-scale renewable-energy projects. The company would be required to buy at least 5 percent of the power it delivers to Rhode Island, and the contracts would last 10 to 15 years.

Christopher L. Whitman, president of Allco Solar, a division of Allco Renewable Energy, said the Coventry project hinges on the state passing legislation that makes the project more economically viable.

“If legislation doesn’t pass,” Whitman said in an interview, “we’re not going to be doing much.”

Allco is supporting the Sullivan bill, which sets the rate at which electricity from solar energy would sell for: 48 cents per kilowatt hour. That is about five times the rate that National Grid now pays for electricity under its current standard offer contracts. The additional cost would be passed on to all ratepayers.

Michael Ryan, who heads National Grid’s operations in Rhode Island, said that if the company were required to buy 10 megawatts of electricity at 48 cents per kilowatt hour, it would cost Rhode Island electricity customers a total of $12 million to $15 million a year. That would have the effect of raising electric bills by about 1 percent, Ryan said.

Sullivan, the bill’s sponsor, had different cost figures. He said the average customer would have to pay only about 20 cents a month more to support the purchase of electricity produced by the Allco solar project.

National Grid supports the Montalbano bill, Ryan said, because it gives the company some discretion about who it will buy renewable energy from and at what price.

“Just because it’s a renewable project doesn’t mean it’s a good project,” he said.