In December 2000, the San Elijo Joint Powers Authority Water Reclamation Facility in Cardiff-by-the-Sea, CA, saw energy costs triple in a single month. San Elijo Assistant Manager Mike Thornton and his team needed an alternative for viable, economical power production. With a goal of following California's "Flex Your Power" initiative to conserve grid electricity, San Elijo began investigating onsite power generation options.
The authority selected a system featuring the Capstone MicroTurbine. The microturbines were attractive because of their low scheduled maintenance and low emission design, plus their ability to run on biogas which the San Elijo plant produces in abundance.
Capstone distributor MWH Energy Solutions (www.mwhglobal.com/power.asp) designed San Elijo's system comprising three Capstone C30s. Thornton's team managed the installation by Orion Construction.
"We gave this engineering team an unrealistic schedule of just three months to complete our conceptual design and subsequent construction," said Thornton. "MWH Energy Solutions, Capstone Turbine and Orion Construction did an outstanding job of working with amazing speed, cooperation and flexibility to successfully complete the project."
To fuel the C30s, digester gas is compressed, dried and filtered before use. The three Capstone C30s generate up to 80 kW of electric power (net of compressor load), representing roughly 15% of the plant's total demand. This reduces the amount of electricity that San Elijo must buy from the grid, lowering its power costs.
At the same time, hot exhaust from the microturbines is captured and used to heat water needed at the reclamation facility. The process is known as CHP—combined heat and power. One generator system uses one fuel source to yield two usable energy outputs with very high fuel efficiency.
The Capstone MicroTurbine system emissions are substantially lower in methane and NOx than emissions from standard flaring and less than those from reciprocating engine gensets.
In his cost benefit analysis of the system, Thornton considered all the variables including system performance, grid electricity costs and eligibility for grants through the use of onsite power.
"When you look at all the factors, including current electricity prices and grant funding, we're anticipating payback in three to four years," Thornton said. "We're seeing a drop in monthly electricity costs of $4,000 to $4,500."
A California Energy Commission grant contributed to the favorable ROI calculations. Thanks to onsite power from the microturbine system, the facility received $300 per kW of peak load reduction for a total exceeding $25,000.
In September 2002, the San Diego Regional Energy Office (www.sdenergy.org) awarded a $76,000 rebate check to the San Elijo Joint Powers Authority from San Diego Gas and Electric's Self-Generation Incentive Program that promotes the use of clean, efficient distributed generation.
Conclusion
In choosing the Capstone MicroTurbine, Thornton and the San Elijo management team reduced grid demand, resulting in significant cost savings and a cleaner environment.
"We had a waste gas, a byproduct of the treatment process that we were not capitalizing on. Now we're capturing it and using it productively," Thornton said. "That makes good sense."
