The answer? Trash, by a mile.
According to the U.S. Energy Information Administration’s most recent Renewable Energy Annual, waste is responsible for 0.452 quadrillion Btus (quads) of renewable energy consumption while solar thermal and PV combined account for only .098 quads. In other words, waste provides nearly 5 times the energy as does solar. Looking at just electricity generation, the difference is even greater: 0.272 quads for waste and only 0.009 quads for solar, a difference of 30 times!1
Energy Consumption for Electricity Generation (quads)
|Wood and Derived Fuels||
Source: EIA Renewable Energy Annual 20091
Energy is produced from waste in two main ways: landfill gas and waste-to-energy. Gas pockets build up within landfills as bacteria break down the municipal solid waste (i.e. trash), producing methane. This landfill gas can be harvested and used to generate power.2 For example, Waste Management, North America’s largest provider of environmental services, gathers landfill gas from 130 of its landfills, producing 550 MW of power.3
Waste-to-energy is a more direct means of producing energy from waste. Instead of being dumped into a landfill, Municipal solid waste (MSW) is directly burned to generate electricity. According to the EPA, there are 87 MSW-fired plants in the U.S., generating 2,500 MW. Burning MSW, however, shares many of the same drawbacks as conventional fossil fuel generation including air emissions, water use and water contamination.4
This month Wired Magazine featured S4, a company that is developing an emissions-free alternative to traditional incineration – plasma gasification. In the first stage of S4’s process, the majority of the MSW input is transformed into syngas within a 1,500o F furnace. A blast of 18,000o F plasma then breaks the remnants into gas products that can be made into fuel or other products. This is an amazing, but energy-intensive process and commercial success will depend on producing more power then is consumed.
We typically don’t think of our refuse an energy resource, but maybe it is about time that we should.
- Renewable Energy Annual 2009, U.S. Energy Information Administration, January 2012. http://www.eia.gov/renewable/annual/pdf/rea_report.pdf
- Landfill Gas, U.S. Environmental Protection Agency. http://epa.gov/lmop/faq/landfill-gas.html
- Renewable Energy. Waste Management. http://www.wm.com/sustainability/renewable-energy.jsp
- Municipal Solid Waste. U.S. Environmental Protection Agency. http://www.epa.gov/cleanenergy/energy-and-you/affect/municipal-sw.html
- Wolman, David. High-Powered Plasma Turns Garbage Into Gas. Wired Magazine, February 2012. http://www.wired.com/magazine/2012/01/ff_trashblaster/