In Business, Creating Sustainable Enterprises & Communities

LAUNCHING “LEFTOVERS TO LIGHTS”

In Business, January-February, 2006, Vol. 28, No. 1, p. 26

Sacramento Municipal Utility District progresses toward reaching its Renewable Portfolio Standard goal of 23 percent by 2011.

Ruth MacDougall

AS IT MOVES FORWARD, to achieving its Renewable Portfolio Standard (RPS) goals, the Sacramento Municipal Utility District (SMUD) will have reached 15 percent by the end of 2006. Renewable energy from biomass is contributing about a quarter of that amount. Making it the rest of the way to 23 percent by 2011 will be challenging because California's RPS mandate has helped create a seller's market for renewable energy.
So SMUD is looking to its own customers to help provide local sources of renewable energy. A check of inventory revealed that municipal solid wastes (MSW) are the largest untapped biomass resource in Sacramento. In addition to construction waste, yard trimmings and MSW, over 200,000 tons of food waste are disposed each year in Sacramento County jurisdictions. With its high moisture content, food waste creates the largest environmental impact. Because it is heavy, food waste contributes significantly to the environmental impacts of transportation, and once in the landfill it contributes to water pollution.
Determining how to turn this resource into energy was one of the reasons SMUD launched the Leftovers to Lights program. Dr. Ruihong Zhang of University of California at Davis (UC Davis), Biological and Agricultural Engineering Department is heading the research. UC Davis just completed an in-depth survey of 45 different businesses within the Sacramento region. The survey targeted large sources of food waste, such as food processors, hotels, hospitals and prisons.
Researchers asked what food waste was being generated, how it was being disposed of, and whether the business was interested in alternatives to disposal. All the businesses interviewed were very happy to participate in the Leftovers to Lights program and eager to see their waste turned into energy. What we found was the potential for almost five megawatts of renewable electricity from the 45 businesses surveyed.
The survey found that a couple of Sacramento businesses have enough waste and enough space to house an on-site digester. Prefeasibility studies have determined that these businesses can also utilize the waste heat recovered from the generator. This method, sometimes called, Combined Heat and Power (CHP) improves the system-wide efficiency and provides a better return on investment.
This spring, SMUD plans to host a forum on anaerobic digestion to provide participants in the Leftovers to Lights Program and others with information about available technologies and options for converting food waste to energy.
To further encourage self-generation of renewable energy, SMUD added biomass to its Solar Net Metering Rate in 2005. This allows the utility to net meter biomass projects in the same way it net meters its customers with solar panels. As SMUD continues working to develop local biomass for renewable energy, it is considering all options, including yesterday's leftovers.

Ruth MacDougall is Biomass Program Manager with the Sacramento Municipal Utility District's Advanced Renewables and Distributed Generation program. She can be contacted via e-mail at rmacdou@smud.org.