tackling climate change
The Biomass solution
It may not be as sexy as biofuels, but biomass power
could be the secret weapon in the war on climate change.
By ChuCk ku TSCheR
Chuck kutscher is a
principal engineer and
manager of the Thermal
systems Group at the
national renewable
energy Laboratory.
he is a past ases chair
and was chair of the
soLar 2006 conference, which resulted in
the ases report, “
Tackling Climate Change in
the u.s.” (Free down-load at ases.org/
climatechange.) he
taught a course at the
university of Colorado entitled “Climate
Change solutions.”
The opinions expressed
here are solely those of
the author.
There’s lots of debate over the pros and cons of biofu- els. When done properly, biofuels can reduce both our need for imported oil and our net carbon emissions. But with all the talk about biofuels, little attention is
being paid to another important use for biomass: electric
power production. If our foremost goal is to address climate
change, it makes more sense to harness biomass for electricity production than to run our cars. (Of course, with the
advent of plug-in hybrid and all-electric vehicles, biomass
power could do both!) Like geothermal power, biomass
electricity is another renewable technology that can compete head-to-head with coal.
There are three basic ways that biomass can be used to
produce electricity: combining it with coal in a pulverized
coal plant, burning it by itself to power a steam cycle and
gasifying it. Whereas direct combustion provides an efficiency of only about 20 percent, efficiencies of 40 percent
can be achieved in an integrated gasification/combined-cycle (IGCC) plant where the waste heat from a gas turbine is captured to operate a conventional steam power
cycle. (Co-locate that biomass-IGCC plant with an industrial process that can utilize low-grade waste heat, and the
overall efficiency of the combined heat and power plant
is higher still.) Biomass power contributes about 10,500
megawatts (MW) of electricity in the United States (
representing about 25 percent of the world total). All of this
is direct combustion (500 MW is co-fired with coal), with
biomass sources including pulp and paper, dedicated biomass, municipal solid waste and landfill gas.
With some exceptions, U.S. biomass resources are
well distributed across the country. A study by Oak Ridge
National Laboratory estimated a 2025 U.S. resource of
about 1.25 billion tons of dry biomass, compared to about
400 million tons today. The future resource assumes
increased agricultural yield and land-use changes such as
no-till farming. The 1.25 billion tons (1.1 billion metric
tons) is comprised mainly of crop residues ( 32 percent)
and other agricultural biomass ( 13 percent), forests ( 27
percent) and energy crops ( 27 percent).
Biomass differs from other renewable energy resources
(solar, wind and geothermal) in that it has a non-zero fuel
cost. The total biomass cost, amounting to $20 to $60 per
ton, stems from planting, management, harvesting, collecting and transportation. Because of the transportation cost,
biomass power plants are typically located within 50 miles
of available resources. This limits plant capacity to about
50 MW (although more efficient IGCC plants could be
Copyright © 2009 by the American Solar Energy Society Inc. All rights reserved.
twice that size), with the average plant producing about 20
MW. Because the biomass resource is well dispersed, there
are many opportunities to locate new plants near existing
transmission lines.
The American Solar Energy Society’s “Tackling Climate
Change in the U.S.” study concluded that biomass power
could provide 110,000 MW of electric power in the United
States by 2030, enough to provide about one-third of the
electricity currently generated by coal. The main hold-up
in deployment is that its electricity cost (about 8 cents per
kilowatt-hour) is not competitive with coal. However, biomass is probably much cheaper than new nuclear power
plants. And if carbon dioxide is eventually priced at about
$30 per ton of CO2 or more, the cost of biomass power
should be on a par with coal.
Biomass power production offers many benefits. Capturing biomass waste products reduces needed landfill capacity.
Collection of forest residues reduces fire danger. Perhaps
most important, biomass power tackles climate change in
a number of ways. It can help shift agricultural emissions
from methane to carbon dioxide, which, pound for pound,
would reduce the global warming impact by a factor of 25.
Studies have shown that the greenhouse gas emissions associated with burning forest residues are much lower than if
those same residues are allowed to decay on the forest floor.
And, as mentioned earlier, biomass power plants can provide baseload power, thus displacing coal plants, the worst
carbon emitters in our nation’s electric grid.
Biomass also has the potential to fight climate change
in a major way that other renewable resources cannot.
Biomass power is usually considered to produce zero net
carbon emissions. (Although biomass emits carbon dioxide
when it is burned, it removes about an equivalent amount
of carbon dioxide from the air as it grows.) But what if we
were to take carbon capture and storage technologies that
are being studied for coal-IGCC plants and apply them to
high-efficiency biomass-IGCC plants? In that case, biomass
power would be far better than carbon-neutral and would
actually draw down atmospheric carbon dioxide. Coupled
with efficiency, other renewables, reforestation and land-use improvements, biomass-IGCC could give us a fighting
chance to eventually reduce atmospheric CO2, currently
at 386 ppm, back down to 350 ppm, where NASA’s James
Hansen says we need to be to stop melting the ice sheets.
So the next time you hear people discussing the benefits
of biofuels, tell them that, when it comes to reducing carbon
emissions, there’s an even better biomass solution. ST
