BioCycle October 2011, Vol. 52, No. 10, p. 61
Last week, the U.S. Department of Energy released an update to its 2005 Billion Ton Study. The premise of the initial study was that the U.S. could supply 30 percent of its transportation fuel needs with mostly forest and agricultural biomass by 2030. The update reinforced the earlier study. The new report includes more details, economics and alternative scenarios, but the conclusions were pretty much the same. “We can do it.”
While that report looks at the biomass supply, ultimately the benefits of biofuels must outweigh the costs of developing them. A few weeks ago, I represented California Biomass Collaborative at a biofuels workshop in Sacramento. It was an important policy event so I collected slides from everyone at the Biomass Collaborative, allowing me the chance to learn as well. One of the slides was on the efficiency of biofuels in terms of miles per ton of biomass. Electricity from biomass was shown to yield many miles per ton as a transportation fuel. Using conservative assumptions, Bryan Jenkins, University of California (Davis) Energy Institute, found that by converting biomass to electricity, a vehicle could travel about 3,600 miles/bone dry ton of biomass. Cellulosic ethanol only got 2,300 miles/ton of biomass.
This was an eye-opener. Converting biomass into electricity is not efficient, with only 25 percent of biomass being converted into power, losing 75 percent of the energy. There are some technologies like combined heat and power (CHP) and the more fledgling technology, integrated gasification combined cycle that allow that efficiency to be higher, but these are not as common as the conventional steam-generating power plants.
Ethanol as a fuel was the least efficient in terms of miles per ton of biomass. This is not so surprising, because ethanol only has two-thirds of the energy value of gasoline. It takes three gallons of ethanol to provide the same energy content of two gallons of gasoline when used in a standard gasoline engine. And while liquid fuels are energy dense and can pack a lot of energy into a small volume, the process of transferring that energy to forward motion in a conventional vehicle is very inefficient, which makes conversion of solid biomass fuel into electricity look pretty good.
VALUE BASED ON ENERGY CONTENT
Comparing the energy value of electricity to ethanol (currently from corn), the value of each energy unit is similar. A residential price of electricity at 12 cents/kWh reported by the Department of Energy has an energy value of about $35/million btu (MMbtu). The wholesale price of corn ethanol reported by USDA in August was $2.84/gallon. This has an energy value of $37/MMbtu. In this context switching from ethanol to electricity doesn’t seem too difficult.
This reasonable situation is compounded by the difficult reality that during the same period of time, gasoline selling retail for $3.60/gallon and diesel fuel selling retail at $3.80/gallon both had energy values around $29/MMbtu. That’s about 80 percent less per energy unit than electricity or ethanol.
It gets worse. These prices are based on using coal and natural gas for most of the electrical power production. Coal prices may be similar to some sources of biomass at around $50/ton, but coal is physically denser (less space for that ton than biomass) and it has an energy content that is about 50 percent higher than biomass. So the 12 cents/kWh price is based on cheap coal. Current corn ethanol is also still cheaper to make than cellulosic ethanol presented in the earlier example from Bryan Jenkins.
VALUE BASED ON EMISSIONS
It is possible that technical efficiency (reduction of slippage) or lowest energy value may not be the best measure of fuel in the future. California is building its future on a low carbon fuel standard (LCFS). This LCFS policy is based on the concept of carbon intensity (measured in grams of CO2-equivalent per energy unit, or in this case, megajoule). This carbon intensity is a life-long, cradle-to-grave estimate of how much carbon dioxide equivalent emissions (CO2e) will be derived from the production and consumption of a fuel. This is not the same thing as the energy value or even the carbon content. It is a measure of imbedded emissions.
The carbon intensities (CI) of the LCFS are in the process of being established and they change as the fuels iterate through various production and consumption pathways. Gasoline used in California has a CI of 95.86 g CO2e/MJ. This serves as the benchmark for the fuel to lower the CI. California electricity currently has a CI of 124.1 g CO2e/MJ. The lower the number, the better the CI value of the LCFS, so electricity as it is generated today is not a low carbon fuel. Corn ethanol has a CI of 68, but is assessed a controversial indirect land use tax of 30 g CO2e/MJ. Midwestern corn ethanol has a total CI that is greater than gasoline. California (pipeline) compressed natural gas (CNG) has a CI of 67.7. Biodiesel from used cooking oil has a CI of 15.84, and CNG made from digester biogas has a CI of 13.45 g CO2e/MJ.
When the LCFS is fully implemented the lower CI fuels will have a price premium and will be in high demand while the higher CI fuels will not meet the CI reduction goals. This hasn’t been fully implemented yet. It might succeed. It will certainly work in ways that the national Renewable Fuel Standards will not work.
There are many factors that must be considered that have not been discussed here. Things like recharging time for electric vehicles on long trips, or increasing energy costs in a fragile economy. Innovations like the Sturman Industries’ new diesel engine (see “Making The World A Smarter Engine,” September 2011) capitalize on all of these factors, which play a vital role in discovering the value of biofuels.
Mark Jenner, PhD, and Biomass Rules, LLC, has joined the California Biomass Collaborative. Burning Bio News and other biomass information is available at www.biomassrules.com.
October 19, 2011 | General
Biomass Energy Outlook: Discovering The Value Of Biofuels
BioCycle October 2011, Vol. 52, No. 10, p. 61