The Federal Energy Regulatory Commission on Sept. 8 granted an original license for a previously unlicensed hydroelectric facility in New England, with that license also covering an upgrade of this facility.
In October 2013, Pepperell Hydro Co. LLC filed an application for an original license to increase the capacity of, and continue to operate and maintain, the existing, unlicensed Pepperell Hydroelectric Project. The project’s authorized capacity being licensed is 2,206.5 kW. The project is located at the Pepperell Paper dam on the Nashua River in Middlesex County, Massachusetts.
Flow from the Nashua River passes through a gated intake structure into a 565.5-foot-long penstock. Flow from the penstock passes through a 25.5-foot-long forebay structure and turbine-bay headgates into a 62-foot-wide, 41-foot-long powerhouse that houses a 640-kW turbine-generator unit, a 735-kW turbine-generator unit, and a 764-kW turbine-generator unit for a total installed capacity of 2,139 kW. Three 30-foot-long, 600-volt transmission lines connect the turbine-generators to the regional grid. Flows from the powerhouse are returned to the Nashua River through three 11.5-foot-long turbine draft tubes.
The impoundment has minimal useable storage and Pepperell Hydro operates the project in a run-of-river mode, where outflow from the project equals inflow at all times and water levels in the impoundment are not drawn down for power generation. Pepperell Hydro releases a minimum flow of 15 cubic feet per second (cfs) or inflow (whichever is less) into the bypassed reach over the spillway year round.
The project uses flows between 138 cfs (the minimum hydraulic capacity of the 640-kW turbine-generator unit) and 1,162 cfs (the maximum hydraulic capacity) to generate electricity. At flows less than 153 cfs (the minimum hydraulic capacity plus the bypassed reach flow), the project does not operate, and all flow is spilled into the bypassed reach. At flows between 153 cfs and 1,177 cfs (the maximum hydraulic capacity plus the bypassed reach flow) the project operates, and 15 cfs is spilled into the bypassed reach. At flows greater than 1,177 cfs the project operates at its maximum capacity, and all remaining flow is spilled into the bypassed reach.
The existing project’s average annual generation is approximately 7,668.1 megawatt-hours (MWh).
Pepperell Hydro proposes to install a new minimum flow turbine-generator unit at the existing dam. Minimum bypassed reach flows will pass through a new screened intake structure into a new 24-foot-long penstock. Flow in the new penstock will pass through a new 67.5-kW minimum flow turbine-generator unit and enter a new 4-foot-long draft tube that leads to the upper end of the bypassed reach. The minimum flow turbine-generator unit will have a minimum hydraulic capacity of 15 cfs and maximum hydraulic capacity of 46 cfs. During certain times of the year, flow from the new screened intake structure will be used to operate the permanent downstream river herring passage facility, which Pepperell Hydro proposes to complete and operate.
The project will also include a new 650-foot-long, 600-volt transmission line connecting the minimum flow turbine-generator unit to the existing powerhouse.
Pepperell Hydro proposes to continue to operate the project in a run-of-river mode. As proposed, the project will use flows between 15 cfs (the minimum hydraulic capacity of the minimum flow turbine-generator unit) and 1,208 cfs (the combined maximum hydraulic capacity of the three existing turbine-generator units and the proposed minimum flow turbine-generator unit) to generate electricity. The project will have an estimated average annual generation of 7,813.1 MWh.