Green Tech

It's a gas: the tank for preparing onion juice to be turned into biogas

(Credit: Gills Onions)

Bill and Steve Gill have gone from onion farmers to power producers.

Their company, Gills Onions of Southern California, on Friday will take the wraps off a system that converts up to 300,000 pounds a day of agriculture waste into electricity. At an event at its facility, Gills Onions will receive a check for $2.7 million from SoCal Gas, which offers incentives to customers that reduce natural gas consumption through on-site generation.

One of the main components of the system is an anaerobic digester that converts treated onion plant waste into biogas. That gas is then conditioned and turned into methane, the main component of natural gas. Then the natural gas is fed into a 600-kilowatt fuel cell from Fuel Cell Energy to make electricity.

Gills Onions estimates that the $9.5 million project will have a six-year investment pay back. Among the financial benefits are reducing its electricity bill by $700,000 a year and $400,000 annual savings from handling onion wastes, which used to be spread on their land. The project also received $499,000 from a state waste-to-energy research program.

The technologies to do this sort of waste-to-energy system have been available for some time. But the project, called the Advanced Energy Recovery System, required a group of engineers to assemble and test the pieces as a system based on onion wastes. An important breakthrough in the project was finding a fuel cell that can make electricity from natural gas.

"Many of the things we did took a leap of faith, since nobody knew anything about onion gas," said Steve Gill in the company newsletter.

The combination of products can generate electricity at any farms that generate a large amount of agricultural waste or at waste-water treatment facilities, said SoCal Gas Vice President Hal Snyder, who heads up the utility's research and development. "Any facility that ends up with a bioproduct that an anaerobic digester can work with would work," he said.

A fuel cell from Fuel Cell Energy that can convert methane into electricity.

(Credit: Gills Onions)

SoCal Gas is looking at other ways to generate biogas, including collecting "green waste" from homes and dairy farms. Eventually, methane produced at customers' premises could be fed into SoCal Gas' pipeline.

From an economic point of view, the technology is still relatively immature and requires a hefty up-front investment. But the general direction on cost is favorable, particularly when there are financial incentives to reduce greenhouse gas emissions, Snyder said.

In addition to using its waste for energy, Gills Onions forecasts that it will eliminate the equivalent of 30,000 tons of carbon dioxide per year.

Updated at 8:20 a.m. PT with corrected figure for the amount of onion waste generated per day.