Once upon a time, renewable energy was all about wind and sun. No more. Today, the pressure to cut back on greenhouse gases has shifted attention to biomass, a.k.a. biofuels. That's jargon for recently-living-but-now-dead things that can be burned, digested, fermented, decomposed, reformulated, or otherwise converted into usable energy.
Biomass is second only to hydroelectricity as a source of renewable electricity in the United States, providing 7 gigawatts (billion watts).
Dead stuff has some advantages.
Biomass:
can be used for electricity, heating, cooking or transportation (think ethanol).
Switching to grass
Biomass can be used in many ways. When garbage decomposes
at landfills, it makes methane gas, which can be collected and burned.
Sawdust and other waste from wood processors is the major source of U.S.
biomass electricity.
Switchgrass produces lots of energy -- from the equivalent of two to 10 tons of coal per acre. In many tests, it has worked with existing electric generators. Department of Energy
Biomass can also be grown as a crop. In Iowa, for example, 50,000 acres of switchgrass is being baled and burned along with coal. The grass provides enough heat to make 35 million watts of electricity.
Switchgrass is a native prairie plant that grows about 10 feet tall. Since the plant is a perennial, it greatly reduces soil erosion, especially on steep slopes unsuitable for corn and other row crops. The dense mat of roots stores up to 80 percent of the carbon contained in the plant.
Christopher Kucharik, a scientist at the Center for Sustainability and the Global Environment at the University of Wisconsin-Madison, is looking at the carbon-cycle impact of switchgrass and other prairie plantings in southern Wisconsin.
Finding out how much carbon is actually being stored can be a slippery assignment, he says. "In the summer of 2001 I studied 14 paired sites, where a restored prairie was next to a business-as-usual cropped field. After 10 or 15 years of restoration, you should be able to detect a statistically significant difference in carbon storage, but I found that you would have to measure 45 paired sites to get a confidence level of 80 percent" in the storage rate. In other words, the storage was small and variable.
Incredible credits
Rates of carbon storage would really matter after
a market gets established in carbon credits. These would allow electric
utilities to buy credits in stored carbon to offset the carbon they dump
into the atmosphere. The market would be patterned after the market that
has reduced emissions of sulfur oxides, a source of acid rain. But given
the variability from one site to another, and the expense of gathering
data, the carbon market could raise more accounting questions than an
Enron energy hustle. "It takes a lot of work to come up with good comparison
sites, get the landowner's permission, take the samples and get them processed,"
Kucharik says. "I think people are counting on this too much."
This coal-fired power plant in Madison, Wis., tested the combustion of
switchgrass. When added to coal, the grass was successful. But coal is
cheaper.
Nevertheless, carbon storage is an essential factor in the global warming debate, since a great deal of the historic rise in atmospheric carbon dioxide reflected deforestation and the plowing of virgin soils. "Not many people realize that from European settlement to 1950, the change in land use, and the loss of [carbon-bearing] organic matter was a large contributor to rising atmospheric carbon dioxide," he says, adding that only after 1950 did fossil fuels take priority.
Still, Kucharik says carbon sequestration in the soil is at best a short-term solution to global warming. "Soil is limited for storage, I agree. From the measurements I've seen, there is an upper limit."
Does biofuel make any energy?
Biofuels don't make much sense unless they are a net
energy source, and some experts question that assumption. The corn-to-ethanol
program, which now makes about 1.5 billion gallons per year, is a politically
motivated effort that makes no net energy, according to David Pimentel,
professor of ecology and agricultural science at Cornell University.
Pimentel, who formerly chaired a U.S. Department of Agriculture panel on the energy aspects of biofuels, says, "With ethanol from corn, there is no net energy production. It actually takes almost 1.5 gallon of oil per gallon of ethanol."
Pimentel calculates that the average U.S. auto, driven 10,000 miles a year on pure ethanol, would require corn from 11 acres -- enough land to feed seven people. If all U.S. cars guzzled pure ethanol, he adds, corn would have to cover nearly the entire U.S. land surface.
Not!
Switchgrass
being loaded for transport to a coal-fired generator in Ottumwa, Iowa.
U.S. Department
of Energy
Some kinds of biomass energy make sense, Pimentel says, particularly waste material. Pimentel was not sure about the energy costs of making electricity from switchgrass: Although it would be a crop, unlike corn, it would require no annual tilling.
But even if using cropland for energy crops makes sense now, he suspects it won't in the future. Oil imports are rising, and the U.S. population will, at the present rate, double in about 70 years. "In the short term, it may be okay, but in the long term, it won't work," he says.
If oil imports continue rising, they will have to be paid for. "We will have to use some land to grow food to exchange for oil; there will be a lot of pressure on land."
It's enough to make us want to buy a hybrid car!
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