Long Island can produce or secure enough renewable energy -- solar, wind, hydropower -- to satisfy the needs of every household in the LIPA territory by 2020, and derive sufficient green energy for nearly all power needs by 2030, according to a new study.

The report, titled "A Clean Energy Vision for Long Island," set for release Tuesday at Farmingdale State College, comes as the Long Island Power Authority is making key decisions about future energy sources, most of them fossil-fuel based. By year's end, it could sign contracts for up to 2,500 megawatts of new power from gas plants and cable connections to distant grids, and renew a contract with National Grid to keep the current antiquated steam plants producing.

The new report was authored by Synapse Energy Economics and funded by the Long Island Community Foundation and the Rauch Foundation. Synapse says on its website that it provides reports and regulatory support to consumer advocates and environmental organizations, among others.

It shows that with a strategic balance of rooftop and large, ground-mounted commercial solar arrays, an offshore wind farm supplemented with upstate land-based wind, and lesser amounts of hydropower and other renewables, Long Island could sharply reduce its need for fossil-fuel burning plants to less than one-fourth of the total supply over 20 years.

The scenario envisions using clean-energy credits earned from the renewables to purchase backup capacity from efficient gas-burning plants, which is needed for the times when wind and sun facilities aren't producing -- in the 2030 scenario representing around 25 percent of the available power.

Most of the renewable power would come from wind energy: by 2030, the report suggests, around 2,250 megawatts of offshore wind energy would be connected to the LIPA grid. There would also be some 800 megawatts of energy storage, likely batteries. There would be 900 megawatts of solar placed strategically around the Island.

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The cost to ratepayers over the period would represent an overall increase of between 8 percent and 12 percent above LIPA's projected rates, with the larger impact coming sooner, according to the report.

Implementation of energy-efficiency measures, designed to cut usage, would be key to reaching the goal.

It's unclear how the new report will impact LIPA's new energy plans. Trustees were expected to vote on LIPA's new energy contracts for plants this month, but it is expected that could be moved back to October, as Gov. Andrew M. Cuomo reviews plans to reform the power authority. Cuomo's staff has been briefed on the study.