Biogas Cogeneration Providing Electricity & Cost Savings
The Winnipesaukee River Basin Program (WRBP) is the state-owned wastewater collection system serving portions of the New Hampshire Lakes Region. The WRBP’s Franklin Wastewater Treatment Facility (WWTF) is operated by staff from the New Hampshire Department of Environmental Services (DES). Working for NH DES and the New Hampshire Office of Energy and Planning, Tighe & Bond completed an evaluation of the technical and economic feasibility of a biogas cogeneration project at the WWTF.
Currently, biogas produced during anaerobic digestion is used to heat the digesters and the facility’s operations buildings with supplemental fuel oil required in colder months. When the digesters and buildings require less heat in the summer, a large portion of the biogas is currently flared off. There is an opportunity to use this biogas to generate electricity to supplement the facility’s energy draw from the grid. At the same time, excess heat from the generation process would still go to serve the existing heating load. This would add value to the biogas used in the current system and reduce the amount of flared biogas, representing an overall benefit to the facility.
Feasibility Study Results
The study results indicated that a 250 kW cogeneration system would generate a significant amount of the WWTF’s electricity load without exceeding it, directly offsetting electricity use. Also, the cogeneration system would produce sufficient thermal output to satisfy the majority of the WWTF heating load, including the digesters and the digester building. However, supplemental fuel oil would be required since the existing digester heating capacity will be reduced. Taking this into consideration, the 250 kW cogeneration system is economically viable and could provide an additional revenue stream for the WWTF, paying for itself in approximately six years if owned by DES.
Since DES does not have any capital funds available for project implementation, the project economics were modeled in a scenario where a private developer would own the system. The benefits to the WWTF would be electricity cost savings through participation in net metering and a Power Purchase Agreement. The project remains financially viable from both parties’ perspectives in this scenario, although marginally.