Archimedes screw small hydro in CT

Combining old and new, a recently built hydropower project in Connecticut is demonstrating the capability of a modern turbine design based on ancient screw-like technology -- while using commercial and regulatory structures including a virtual net metering power purchase agreement and green bond financing.

At issue is the Hanover Pond Dam Hydroelectric Project, developed by New England Hydropower Company, LLC. Originally described in a 2013 application to the Federal Energy Regulatory Commission for a preliminary permit and the Commission's subsequent order issuing preliminary permit, the project is located on the Quinnipiac River in Meriden, Connecticut. The run-of-the-river project uses the water power potential of the pre-existing Hanover Pond dam, plus new facilities including a 46.5-foot-long, 11.65-foot-diameter 220-kilowatt Archimedes screw turbine-generator unit. While screws have been used to pump water for over 2,000 years, some modern developers of small hydropower projects are turning to screw turbines in the hopes that they can produce power in a cost-effective and environmentally acceptable manner.

Financed with a combination of public and private capital, including the first official "Green Bond" issued by the Connecticut Green Bank, the Hanover Pond Dam project has been described as the first commercial Archimedes screw design placed into service in the U.S., although similar technology has been deployed at other sites around the world.

On May 19, 2016, the Commission issued an order granting the project an exemption from licensing under the Federal Power Act. The Hanover Pond project was built and placed into service last year. On February 23, 2017, the project gave notice that it would commence commercial generation later that spring, and entered commercial operation in April 2017. The project sells its estimated 920,000 kilowatt-hours of annual power production to the host municipality under a 20-year power purchase agreement designed to fit within Connecticut's virtual net metering regulations.

Operational considerations matter too. According to an article posted by the local Record Journal, earlier this month "a malfunction with the Archimedes screw caused a loud noise and smoke, damaging the hydroelectric dam’s generator." A subsequent incident report filed by the company has not been made public, but an accompanying public cover letter references a "February 5, 2018 sluice gate malfunction."

The Hanover Pond Dam project illustrates some of tensions facing small hydropower projects today, and the challenge of packaging a site with appropriate technologies, commercial arrangements and regulatory structure. Society already has a number of existing dam sites which could be redeveloped to generate hydroelectricity. Technologies -- whether new or ancient -- can harness the power of water moving through or around those dams. Commercial arrangements and regulatory structures -- like green banks and green bonds, power purchase agreements, and virtual net metering regulations -- can make or break a project. At the same time, hydropower operators must remain focused on practical concerns for safe and reliable operation.When it all comes together, it can be win for the community and for the developer.