Solar energy isn't the only renewable resource: there's also garbage.
A company called AgriPower will begin production next year of a movable power generator fueled by a wide range of waste products, from walnut shells to discarded tires.
Although solar and wind energy are the best-known renewable energies, generating power from biomass is getting a closer look, as societies try to diversify their fuel sources.
AgriPower's combined heat and power system was originally envisioned for developing countries that could burn agricultural wastes to make electricity and heat.
The multi-piece unit includes a large feed hopper that holds 5 tons of material, and a high-temperature incinerator that vaporizes biomass as it comes in. The resulting heat can be used to turn a turbine to make 300 kilowatts of electricity. The heat can also be used to power other processes like heating.
As the company gets closer to manufacturing--with first commercial products anticipated next April--it is finding a much wider set of potential applications, said CEO Barry Berman.
The company is seeing interest from landfill operators who, short on space for burying trash, would rather incinerate their waste to produce power and sell it to utilities.
The company is also talking to supermarket chains in the U.K. and France that have to pay more than $150 per ton in "tipping fees" to get rid of organic trash such as discarded produce, cardboard and paper.
"If you are producing any waste stream and you are paying someone to bring it to a landfill, you gotta be nuts," said Berman.
For industrial processes that use diesel engines, AgriPower's system pays for itself within a year, he said. A wood mill, for example, could incinerate sawdust and other waste to make power to run its machines, rather than run off diesel power.
There are already large-scale combined heat and power systems that use biomass as fuel to make on-site electricity. Incinerating municipal waste to make power is also done in almost 90 locations in the United States, according to the Solid Waste Association of North America.
Municipal waste is increasingly segregated, which means on-site power production using a specific material is now a more viable option, said Berman. Another company, Ze-Gen, is testing a process called gasification with construction and demolition debris as fuel.
Berman said that its generator has been tested with a range of materials, including corn husks, corn cobs and sugar cane residue, called bagasse, as well as tires and non-recyclable plastics. Because it generates heat, the unit can dry material like chicken waste before incinerating it, he said.
The polluting emissions from the unit, which is 75 percent efficient, has been tested in several U.S. states and European countries. It met emissions requirements in Switzerland and California, which are stringent measures, said AgriPower vice president Anthony Kahn.
The incinerator uses a construction called a bubbling fluidized bed--essentially a layer of sand heated to high temperatures--and vaporizes waste within seconds of entering the furnace.
Although the output of the initial unit is a fraction of an industrial power plant's capacity, AgriPower's 80,000-pound generator can easily be transported and usually installed within two days. That mobility is important to using biomass for power production, said Berman.
"It can be brought to remote areas and be brought to where the fuel is located," he said. "A rather significant problem in biomass is gathering it and bringing it to a furnace to burn it."