Hawaiian Electric Co. estimates that using primarily solar power instead of wind to help meet its renewable energy targets could boost the cost of electricity production by as much as 18 percent.

HECO, which had been working with two companies to develop about 1,500 gigawatt-hours of wind energy on Lanai and Molokai, was ordered by the state Public Utilities Commission in July to consider other renewable energy sources for half of the project.

The wind power project, refered to as "Big Wind," was intended to generate power on Molokai and Lanai and ship it to Oahu via an undersea cable. That project suffered a setback when the developer for the Molokai portion of the wind power project pulled out.

HECO produced four alternative scenarios for the PUC using utility-scale wind, solar, biofuels and a blend of solar and biofuels as the primary source of renewable power generation. The estimates were included in a document HECO filed with the PUC this month.

Hawaiian Electric has a goal of generating 40 percent of its energy needs from renewable sources by 2030.

The study showed that wind is the cheapest of the four alternatives.

"In any event, the scenario analyses described … indicate that for the island of Oahu, interisland wind is a reasonable and cost-competitive renewable energy resource option for meeting the company’s renewable portfolio standard goals, with the added benefit of being commercially available on a large scale with no fuel costs," according to the HECO filing.

In the report to the PUC, HECO officials repeated their frequently stated assertion that there is "no single renewable energy resource capable of providing a ‘silver bullet’ hedge against oil price volatility."

Meeting the goal of generating 40 percent of HECO’s need with renewable energy will "require the addition of multiple sources of renewable energy to the Hawaiian Electric Companies’ systems," they said.

The study said the cost of using wind as the primary source for HECO’s renewable energy in 2030 would be between $524 million and $599 million. The cost estimate for using utility-scale photovoltaic projects as the main source of generation ranged from $617 million to $661 million.

HECO said each of the three alternatives was more expensive than wind:

» Solar by as much as 18 percent.

» Biofuel by as much as 41 percent.

» Mixed solar/biofuel by as much as 33 percent.

None of the scenarios factored in a proposed undersea transmission cable that would add a significant cost to any renewable energy project based on a neighbor island.

The PUC told HECO to consider alternatives that could be sited on any island that could be "reasonably reached" via an undersea cable, or on Oahu itself.

Each scenario assumed equal growth of other forms of renewable energy production, such as garbage-to-energy, ocean thermal energy conversion and rooftop photovoltaic.

In its calculations, HECO assumed that wind turbines would have a capacity factor of 42 percent, meaning that they would be able to generate 42 percent of their maximum rated output over the course of a year. The capacity factor for solar panels was estimated at about 20 percent.

HECO said it is moving forward with plans to build more utility-scale alternative power generation plants and expects to begin accepting bids from prospective developers by this fall.