Prized for fine dining, Napa Valley restaurants could be equally valued for their unsavory waste products — fats, oil and grease.
Napa Sanitation District wants these throw-aways as fuel to generate electricity, saving the district what it said was potentially several hundred thousands dollars annually in utility costs.
The district expects to pay Pacific Gas & Electric $810,000 this year to run its south Napa treatment plant and pumps, an increase of $100,000 from the year before, said Darcy Aston, a district analyst.
To reduce this expense and cut back on greenhouse gases, the district commissioned an Alternative Energy Study in February to see if there was a better way to run things, Aston said.
A consultant, HDR Engineering, looked at the potential for the treatment plant to produce electricity from wind and the sun’s rays, but the results weren’t encouraging, Aston said.
For wind generation to be feasible, steady speeds above 9 mph are desirable. Winds at the plant typically fall between 6 and 10 mph, Aston said.
Solar power turned out to be financially impractical, with a payback of 15 to 33 years on the district’s startup investment, she said. The district had been looking at payback within 10 years.
The best option for alternative energy turned out to be FOG, the acronym for “fats, oil and grease,” Aston said.
Napa Valley restaurants generate lots of FOG, most of which is now carried by commercial haulers to a recycling center in the East Bay, Aston said.
If Napa Sanitation created its own facility for generating energy from fats and grease, the consultant estimated that the district’s PG&E bill might be cut by a quarter, she said.
As it turns out, micro-organisms love to eat fat and grease. And when they do, they produce methane gas as a waste product, Aston said. This methane can be collected and burned to generate electricity.
By feeding fat to bugs, the district could potentially meet 40 percent of its energy demand from alternative sources, the consultant reported.
The district is already extracting methane from sewage in a limited way. Up to 15 percent of the treatment plant’s energy needs are being met through cogeneration, Aston said.
In October, the district’s board of directors asked staff to further study the potential for a FOG facility, Aston said.
By charging the same or less than competing FOG operations in other counties, the district should be able to attract haulers who wouldn’t have to drive as far to dump their cargo, she said.
According to HDR Engineering, which was paid $141,000 for the alternative energy study, a grease receiving station would cost $640,000.
The district would recoup this investment in less than three years, said Brian Thomas, the district’s capital program manager.
The district hasn’t given up on wind and solar power, Aston said. Staff will stay on top of changing costs and potential government rebate programs that would improve the economics of these attractive alternative energy sources, she said.
Buying power from “green” sources that tap wind, solar and geothermal was also studied by HDR Engineering, but the costs were considered too high, Aston said.
The district’s board of directors is interesting in potentially using revenue from a FOG program to offset the higher cost of buying green power, she said.