In California, the United States could produce enough energy each year by harnessing waste — from landfill refuse to cow manure — to power the states of Oregon and Washington, all while cutting the equivalent of 37 million cars’ worth of carbon.
That’s according to research published in Nature Energy from UCLA. Researchers examined this variability by conducting life cycle analyses, or examinations of products from creation to end of life, of four types of waste: agricultural, forestry, landfill and cow manure.
The study encompassed 15 energy conversion technologies and 29 waste types. In their analysis, the researchers combined existing data from the literature on waste conversion technologies with local waste availability from base-year estimates and electricity portfolios to determine relative energy gains and emissions reductions.
Because burning of bioenergy products themselves produces greenhouse gas emissions, the ability of bioenergy to reduce overall greenhouse gases is tied to the energy replaced, making local context important. The greenhouse gas savings from use of bioenergy to produce electricity, for instance, would be greater in areas where electricity comes from carbon-based fuels like coal, as opposed to areas that generate a lot of solar and wind power.
Overall, the study found that the U.S. has the potential to generate 3.1 to 3.8 exajoules (a measure of energy) of renewable energy each year using available waste resources. By comparison, the entire states of Washington and Oregon consumed about 3.3 exajoules of energy in 2017, according to the Energy Information Agency. The study also concluded that using waste products has the potential to displace 103 to 178 million metric tons of carbon dioxide emissions — an amount equivalent to taking 37 million passenger vehicles off the road based on typical passenger vehicle emissions of 4.6 metric tons of carbon dioxide each year.
A key finding was that no one method of bioenergy production maximizes net energy gain, renewable energy gain and climate benefits. Some create more renewable energy, but require more energy to do so, resulting in less overall greenhouse gas emissions savings. Thus, identifying the optimal bioenergy application in any situation depends on the intended outcome.