What Is It, and How Does It Produce Electricity?
Rather than wait for a field crop to grow and be harvested to take whatever residue is left for electric generation, why not plant and harvest crops specifically for electrical production? Food and timber crops aren’t necessarily the best source of biomass for feeding into a power plant. Power plants need crops that grow fast and produce lots of bulk with minimal water content.
Three crops are considered prime fuel for electrical generation: switchgrass, hybrid poplars, and hybrid willows. Corn is not an energy crop used for electrical generation. It is used to produce liquid ethanol (a substitute for gasoline). In addition, several saltwater and aquatic plants (kelp, rushes, and reeds) have been tested and used for energy production. Kelp, especially, is attractive as an energy fuel because several of its chemical components are routinely used by the cosmetic and food industries. However, because of their high water content, these aquatic plants are better suited for conversion to methane (see page 114) than for direct burning.
The concept of planting vast fields of energy crops will certainly work. But it comes with a caution. In early 2000s the United States experienced a well-publicized move to grow corn as a fuel crop. Thousands of acres were converted to fuel-corn production to produce ethanol. When oil prices spiked above $100 a barrel, corn as a fuel crop had its moment of fame. However, shifting acres of corn to fuel production tightened the supply of corn for food. Corn prices spiked. When oil dropped back below $70 a barrel, ethanol from corn ceased to look like the golden future of gasoline. Planners must make sure that the same thing doesn’t happen when crops are grown specifically for electrical production.
Another option exists: Bypass nature all together. Crops grow because photosynthesis in the plants creates energy molecules that the plants use to create mass. We then burn the plant mass to get the energy. Why not skip the plant and go straight from photosynthesis to energy molecule to electricity? Leaves suck in CO2 and sunlight to produce energy (in the form of sugar molecules) and oxygen. Why not create an artificial “leaf’ that will produce energy molecules (ethanol—a substitute for gasoline or for pure hydrogen) while it cleans C02 out of the air and replaces it with pure oxygen? That is the idea of much worldwide research. No one has built a working plant yet, but many groups have build prototypes in the lab.
What’s Happening Now?
Until 2000, no power plants in the United States used biomass fuel that had been specifically grown as an energy crop. However, there has been a flurry of testing and experimenting during the past decade.
Native switchgrass used to cover the vast American prairie. By the early 1900s it had been almost completely wiped out. Beginning in the 1990s, government and university groups began a program to return switchgrass to the region to stabilize the soil and stop erosion. Native switchgrass species are drought and disease resistant, have low rain requirements, grow well in arid land, and rapidly grow thick tangles of biomass. By the early 2000s it was clear that switchgrass was an ideal energy crop.
The Ottumwa Station power plant in Iowa produces 200,000 tons of switchgrass on over 40,000 acres. The plant runs 100 percent on this fuel seasonally (late spring through fall) while the grass grows and can be regularly mowed.
Test groves of hybrid poplars (545 trees per acre) have been planted in the Pacific Northwest and in several Southern states. Wood from these trees will be harvested after six, eight, and ten years’ growth. Test groves of hybrid willows have been planted in two Northeastern states (6,200 trees per acre). They will first be harvested after only four years of growing and can be regularly recut thereafter, until they must be replanted after twenty-two years.
Although switchgrass has generated the most excitement, all three crops are being carefully watched to see if they have the potential to significantly contribute to the national electrical grid.
The Helios project at the University of California, Berkeley, is the current leader in artificial photosynthesis research. Their primary goal is to find a substitute for gasoline. They have successfully built thin, black Helios leaves that soak up sunlight and drip ethanol into metal trays that collect the liquid energy.
How Does It Measure Up?
(The Good, the Bad, and the Ugly)
On the plus side for energy crops:
• Energy crops are renewable and low in sulfur.
• These plants don’t add to the atmosphere’s C02 burden, because growing them removes C02 from the atmosphere. Thus, when it is re-released during burning, no new C02 is added—just the same C02 that was originally in the air.
On the negative side for energy crops:
• Energy crops require vast amounts of land for the amount of energy they produce. The Ottumwa Station plant, for example, takes more than 40,000 acres of prime agricultural land out of production for food. And that is just one plant. If biomass power plants using switchgrass were to become a significant contributor to the national grid, and various utilities built hundreds of plants, easily 4.5 million acres of
land could be dedicated to that one energy crop. The society would have to decide if that is the best and most appropriate use for scarce agricultural land.
What’s the Bottom Line? (How Much Can It Help?)
• Potential: Use of energy crops is limited by land use requirements. This is a regional, not a national, energy technology.
• Key Factors: Bio crops require massive amounts of prime agricultural land. Even a modest-sized plant can use 40,000 acres of land and produce only enough bio crop for seasonal energy production.
• Timeline: Look for demonstration bio crop plants to go online by 2012. However, expect only limited, regional development thereafter.
Classroom Activities
1. Growing crops specifically to feed them into utility boilers is a specialty activity, not something that we can easily duplicate in our own community. Research the three energy crops discussed above (switchgrass, hybrid willow, and hybrid poplar). What makes them good crops to use as boiler fuel? Are there other crops that could be used as energy crops? See if you can find one or more as you research this topic at the library and online.
2. Do you think it is a good idea to use agricultural land (along with related resources, like water and fertilizer) to grow crops just to be fuel for electric power plants? When would it be a good idea? When wouldn’t it? What about growing kelp in coastal ocean waters to convert into an energy fuel?
Let each student develop his or her own opinion and then hold a class debate to compare points of view.
For Further Reading
de la Garza, Amanda. Biomass: Energy from Plants and Animals. Chicago: Cengage Gale, 2006.
Johanson, Paula. Biofuels: Sustainable Energy in the 21st Century. New York: Rosen Publishing Group, 2010.
Ollhoff, Jim. Geothermal, Biomass, and Hydrogen. Edina, MN: ABDO Publishing, 2010.
Povey, Karen. Biofuels. Chicago: Cengage Gale, 2006.
Reynoldson, Fiona. Understanding Geothermal Energy and Bioenergy. New York: Gareth Stevens, 2010.
Thomas, Isabel. The Pros and Cons of Biomass Power. New York: Rosen Publishing Group, 2007.
Walker, Niki. Biomass: Fueling Change. New York: Crabtree Publishing, 2006.
Web Sites
www. eia. doe. gov > … > Electricity Analysis Reports
The Energy Information Administration site on biofuels.
www. mpoweruk. com/biofuels. htm
A good description of the process.
bioenergy. ornl. gov/reports/fuelwood/toc. html
A site that focuses on producing trees as an energy crop.
www. treepower. org/
An advocacy site for growing trees as an energy crop.
www1.eere. energy. gov/biomass/pdfs/consortium. pdf
A site describing related activity in the Northeast.
bioenergy. ornl. gov/papers/misc/switgrs. html
A good paper on using switchgrass as an energy fuel.
www. switchgrass. nl/
An advocacy site for using switchgrass as an energy fuel.
