HANCOCK — The cluster of 10 wind turbines atop Brodie Mountain will soon grow to an even dozen.
The Berkshire Wind Power Cooperative Corp. is planning to install two additional turbines to its Berkshire Wind project this fall.
Representing Phase 2 of the project, two 2.3-megawatt capacity turbines will be erected just to the north of the existing 10 1.5-megawatt turbines. The new turbines will bring the wind farm's generating capacity to 19.6 megawatts.
The cooperative is an initiative of the Massachusetts Municipal Wholesale Electric Co. and 14 of its member municipal utilities participating in the first phase of the project. Participants in this second phase of the project include the municipal utilities in Boylston, Chicopee, Hull, Ipswich, Marblehead, Peabody, Russell, Sterling, Wakefield and West Boylston.
David Tuohey, a spokesman for the company, said the board's approval of the project reflected the desire of its member utilities to access more electricity generated by renewable sources.
"What drives that is the desire of their customers to be more involved in clean energy projects," he said.
When it began operation in 2011, Berkshire Wind was Massachusetts' largest inland wind farm. Today it is the state's second largest wind farm.
Since it started generating power, the farm has been averaging 40 percent of capacity, which is relatively high for an inland wind farm, Tuohey noted.
Officials are in the process of selecting a firm to manufacture the turbines, and as such are not aware of the turbine heights yet. The existing turbines are 385 feet tall.
The first phase of the project cost about $45 million and generates enough to power 6,000 homes. That number is expected to rise by 1,840 more homes after the other two turbines are activated.
Officials won't know the cost of Phase 2 until the turbine prices have been negotiated.
They also have yet to go through the permitting process, although, Tuohey noted, an agreement with Hancock has been reached.
"It's still early in the process," he said.
The goal is to begin construction in the fall, and activate the turbines in the spring.
The possibility of adding two turbines was anticipated, so when the original phase was built, access roads were built and pad sites cleared, so the only work will involve the transport and erection of the towers, minimizing environmental impact to the Brodie Mountain ridgeline.
Improvements in blade technology will allow the new turbines to begin operating and generating power at lower wind speeds, further increasing potential output for the wind farm. The turbine blades will utilize a feathered blade trailing edge, reminiscent of a bird's wing, to minimize blade wake and sound levels.
Scott Stafford can be reached at firstname.lastname@example.org or 413-629-4517.