Biomass Energy Efficiency
To make a gallon of ethanol, start with 23 pounds of corn with a potential energy of about 185,000 BTUs. Add 40,000 to 80,000 BTUs of fossil energy per gallon and you get a gallon of ethanol containing 77,000 BTUs. Therefore the efficiency of the corn-to-ethanol conversion, including the fossil energy, is around 30%. Ethanol isn’t a very efficient motor fuel, so the conversion from heat to mechanical energy is around 15%. Really only about 5% of the energy in the corn is used to turn the wheels of the vehicle. No wonder ethanol requires subsidies of $0.50 to $1.00 per gallon, including the corn subsidies!
Biomass Energy in the Home
If you burn the corn in a pellet stove, you would harvest around 75% of the corn’s potential energy in space heat.
Pellets are a very efficient bio-fuel compared to ethanol. Pellets yield from 5 to 10 times the fossil energy required to harvest, process, and transport their biomass. You can get 75% of the potential energy out of the pellets as space heat! If we were as sophisticated as the Europeans, who are making electricity and heat from pellets and wood chips, we could get up to 85% of the potential energy out of pellets or wood chips. This process is called “Combined Heat and Power”. CHP might be our best option for biomass conversion to a transportation fuel. It would allow charging electric cars with electricity generated from biomass CHP.
Options Going Forward
What if we spent the $10 billion annual corn/ethanol subsidy to purchase conservation electricity or to plant trees in strategic places? With $10 billion we could purchase about 25,000 average megawatts (assuming around 5 cents per saved kilowatt-hour) of conservation power worth around $20 billion retail electricity cost. This could reduce the summer peak around 3 percent (of the 780,000 megawatt total).
If we attacked the summer peak energy-use directly, by planting shade trees in strategic places such as the west-facing windows on low-rise buildings, we could save about the same amount of electricity. This would also generate the same quantity of wealth. You could plant 50 million 18-foot-tall trees for $200 each to spend the $10 billion. Each tree displaces half a kilowatt of cooling electric power. That’s 25 million megawatts or 3 percent of the summer peak. Repeating this process every year, instead of funding the bio-fuels boondoggle, would create enough new power to halt the construction of new coal-fired power plants in the US.