Would the capacity of a proposed electricity cable from Block Island to the mainland allow for more than the eight wind turbines currently planned by developer Deepwater Wind?

Block Island Power Company President Cliff McGinnes Sr. revealed at Monday's Electric Utility Task Group meeting that the proposed size of the cable to the mainland is 69 kVa (kilovolt-amperes), which surprised task group members and newly hired consultant Richard La Capra.

That capacity "seems awfully high," said La Capra. The cable from the wind farm to the island would be rated 35 kVa, said McGinnes.

The size of the cable relates to how much electricity could be delivered through it.

Deepwater Wind is proposing eight 3.6-megawatt turbines off the island's southeast coast within the 3-mile state limit, with a combined total output of 28.8 megawatts. Deepwater's Andres de Lasa confirmed the cable sizes Tuesday. He said that RFP from National Grid called for a constant delivery of 10 megawatts of energy from the wind farm to the grid, hence the size of the cable.

The company has previously said that the mainland cable would be customized to carry only the combined load of the eight turbines and no more. This had allayed some concern voiced by island residents that more turbines could eventually be installed close to the island.

However La Capra said Monday that in his experience a 69-kVa cable, which could deliver up to 50 megawatts of electricity, was far larger than what is needed for the proposed island wind farm - even allowing for the distance to Narragansett, and the conductivity of potential soil types on the ocean floor.

With such a cable, there "would seem to be room for expansion," La Capra said.

He pointed to Nantucket, which has a 46-kVa cable stretching approximately 26 miles, rated to carry a up to 32 megawatts of electricity.

"Then 46 is more than sufficient," said task group member Barbara MacMullan.

Block Island's historic peak demand is just under 4 megawatts. McGinnes said it had been a few years since BIPCo had seen it that high.

Nantucket ended up installing a second cable due to "huge load growth" - 14 megawatts to 36 megawatts, said La Capra. This explosion of demand corresponded with the arrival of large houses and an expanded use of air conditioning on the island, said LaCapra. Air conditioning "saturation" on Nantucket grew from two percent to 20 percent, said La Capra.

Block Island, in comparison, has a "lower saturation of Wall Street traders," remarked task group member Everett Shorey.

Shorey went on to say that given how close Block Island is to build-out, it was unlikely that demand would ever reach even 10 megawatts.

Shorey said that given the size of the proposed cable, the five-to-eight turbine wind farm could be seen as "a stalking horse for 15 to 20 turbines." He suggested that Deepwater be informed that it would be a "public relations benefit" to reduce the capacity of the proposed cable.

La Capra said he planned to speak to Deepwater CEO Bill Moore soon.

The plan would be to bury the cable in three to four feet under the ocean floor. LaCapra said that a silty bottom would diffuse the heat passing through the cable more efficiently than clay, and that would play a role in how efficiently the cable would transfer power.

From the audience, Town Council member and task group liaison Peter Baute said, "we would have concern" if the number of turbines close to the island were to exceed the proposed eight.

La Capra agreed that it was "an important issue."

The much larger wind farm proposed by Deepwater, to consist of more than 100 turbines approximately 15 miles east of the island, would generate about 365 megawatts of electricity and would require a cable rated at 115 kVa, said La Capra.

Fiber optics

According to McGinnes there is currently no plan to include a fiber optic element to the mainland cable. He said that Deepwater was against it for reasons of interference. However, he said that Verizon expressed interest in a fiber optic option when BIPCo unsuccessfully sought a grant to construct its own cable a few years ago.

Town Manager Nancy Dodge said that Fred Hashaway of the Rhode Island Economic Development Corporations was planning to approach Verizon as well as Cox to see if they had interest in being part of the cable.

Currently Verizon uses the microwave tower on the island to transmit its phone and Internet data.