Santa Barbara Uses Co-Generation For Renewable Energy
The City of Santa Barbara won an Award for Excellence in the Public Works, Infrastructure and Transportation category of the 2006 Helen Putnam Award for Excellence program. For more information, visit www.cacities.org/helenputnam.
The energy crisis that began in California in mid-2000 provided an incentive for the City of Santa Barbara to revisit the feasibility of co-generation.
Increased awareness of both opportunities and technologies for distributed generation made co-generation more attractive. Micro-turbines and fuel cells were emerging as commercially available technologies, making it possible to generate electricity without the increased level of pollutants that would be released by reciprocating engines. Finally, the incentives offered by the California Public Utilities Commission (CPUC) strengthened the case for distributed generation, especially for projects using a renewable fuel such as digester gas.
The City of Santa Barbara operates a conventional activated sludge treatment plant, El Estero Waste Water Treatment Plant (WWTP), with two anaerobic digesters used for solids stabilization. The anaerobic digesters produce methane as a byproduct. In the past, a portion of the methane gas heated the boilers that were used to maintain the digesters at temperature; the remainder was flared. Although flaring the gas seemed a waste of a potential energy source, economic evaluations of installing a co-generation system did not pencil out.
The attractiveness of using digester gas to generate electricity was reduced by two other concerns:
- Reciprocating engines (traditionally used for co-generation at wastewater treatment plants) would create more air pollution than was produced by flaring the gas. As a wastewater treatment facility dedicated to reducing pollution, the idea of increasing air emissions seemed inconsistent with its mission.
- Other smaller treatment plants found that operating and main taining reciprocating engines was a significant challenge for their maintenance staffs. Smaller treat ment plants generally do not have specialized staff dedicated to the operation of a specific unit, as is the case in larger plants. This treatment plant was aging, and the maintenance staff was already facing an increasing workload to keep up with the maintenance requirements of equipment that was nearing the end of its useful life.
The energy crisis that began in California in mid-2000 provided an incentive to revisit the feasibility of co-generation.
The City of Santa Barbara conducted a comprehensive cost-benefit analysis to evaluate the alternatives for co-generation. The results suggested that co-generation was cost effective, but the city had no capital set aside for such a project. Major rehabilitation and replacement of plant processes had been scheduled, and adding another project to the capital improvement program would require deferring needed work on the treatment plant and risking possible violations -
or raising wastewater rates. Given that wastewater rates had recently been raised 10 percent, neither option seemed viable.
Public-Private Partnership for Co-Generation
The city decided to pursue a co-generation project that would not require capital investment of public funds or hiring specialized staff for operation and maintenance of the co-generation equipment. City staff wrote a request for proposals (RFP) to provide a turnkey co-generation facility and sell generated electricity to the city. The RFP specified that the co-generation facility could be sited at the city’s wastewater treatment plant. The city would provide digester gas free of charge and in return would pay a set fee for electricity. Waste heat would be supplied at no charge to heat the digesters as needed.
Staff worked to ensure that the RFP provided respondents as much flexibility as possible. CPUC grant funds for co-generation projects were identified for the successful respondent to offset initial capital costs.
Cost Effective, Environmentally Protective Co-Generation
Santa Barbara received three responses to the RFP, and a project using a 500 kilowatt power plant manufactured for base load electricity and heat generation was selected as the most responsive. The project, the first commercially operated fuel cell plant to use digester gas at a wastewater treatment facility in California, was commissioned in late November 2004. Although there have been a few start-up glitches to work out, the fuel cells have been running effectively since then.
The fuel cell project was selected because it was the cleanest product, would generate the most energy, and provided an opportunity to develop a demonstration project for the local community and other treatment plants. It was also the most economically advantageous. Electricity usage at the El Estero WWTP during the 12 months prior to installation of the fuel cell co-generation plant averaged about 608,000 kilowatt hours per month. The fuel cell co-generation plant can replace approximately 50 percent of this electrical consumption currently purchased from the local electric utility. The price for electricity produced by the fuel cells is set for the 11-year life of the contract at a rate less than grid-delivered power from the local utility. The fixed price of the fuel cell contract should bring further savings to the city as electricity prices continue to rise.
Cost savings from the co-generation plant are estimated to be $20,000 per year, but additional savings could be realized through the sale of pollution credits. An important benefit of the fuel cell operation is the reduction of air pollution from the treatment plant. The type and amount of pollution prevented is equivalent to the amount that a diesel bus would generate if it ran nonstop for 20 months. Although the city is not pursuing sale of pollution credits arising from diversion of digester gas from the flare to the fuel cells, if sold, the value of such pollutant credits would be approximately $50,000 per year.
Santa Barbara ’s innovative approach to developing, operating and maintaining a co-generation facility has resulted in the installation of new technology that serves as a demonstration site and resource for other communities. This project would not have been feasible had the city been required to provide the capital funds for its construction. Partnering with a private company that has expertise in developing electricity projects allowed the city to develop a cost-effective project partially supported by grant funding. The partnership also allows the city to receive continuing operational and technical support and gives the operating company the opportunity to collect data for research and development.
Contact: Rebecca Bjork, wastewater system manager; phone: (805) 897-1914; e-mail: firstname.lastname@example.org.