Chapter 13 Module 38
Biomass
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All energy sources ultimately come from the sun
Biomass includes wood, charcoal, animal products, manure, plant remains, and municipal solid
waste and liquid fuels like ethanol and biodiesel
Biomass is inexpensive and abundant – account for 10% of world energy consumption (higher %
in developing countries)
Can be processed into liquids known as biofuels – only used in limited quantities (easier to burn
a log than to produce ethanol
Biomass is ½ of all renewable energy and 3.5% of all energy consumed in the us.
o 2/3 of biomass in us is from wood and remaining 1/3 is MSW and biofuels
o In developing world larger % comes from wood and animal manure
Modern carbon vs fossil carbon
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Biomass contains carbon, which is released when burned.
Which is better?
o Depends on how material is processed, harvested and how the land is treated. And how
long the carbon has been stored
 Ex. Carbon on plants could have been absorbed thru photosyn as recently as a
few months ago like corn several hundred years ago like in old trees
 Carbon in biomass is modern carbon
 Carbon in fossil fuels is fossil carbon
 Fossil carbon has been buried for millions of years.
 In theory the burning of modern carbon shouldn’t affect net increase in co2
because we are returning carbon to atmosphere where it was recently
 This is carbon neutral. No change in atmospheric co2
Solid biomass
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In the world 2-3 billion people rely on wood for heating and cooking, in us 3 million. 20 million
use wood for energy at least some of the time.
Wood is also used in paper industries, power plants, and by products are used for energy.
Cutting trees for fuel is sustainable if forest growth keeps up with forest use. Forests in Haiti are
overused tho.
Net removal of forest is an unsustainable practice
Results in a net increase in atmospheric co2. Not balanced by the uptake of co2 by photosyn in
new growth
Also releases carbon from soil in a and b horizons. When logging equip disturbs soil
Tree removal in some areas opens up the canopy and actually helps diversity and even increase
photosyn but most often it causes erosion, increase water temp, fragment forest habitats with
logging roads. Tree removal may also harm org that live in the trees.
In developing countries they use wood to make charcoal
o Lighter, twice as much energy, produces less smoke
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o More expensive than wood
o When an area is harvested for charcoal production it is completely cleared of trees
Where wood is scarce, people use dried animal manure as a fuel for heating and cooking
o It removes harmful bacteria from area, reduce risk of disease. But it also releases bad
stuff that causes emphysema and cancer
 Problem is worse when burned indoors with poor ventiliation
Burning biomass produces pollutants like co and no
Biofuels
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Ethanol is made from converting starches and sugars from plants into alcohol and carbon
dioxide. Used as a substitute for gas and diesel.
90% of eth is made from corn and corn byproducts but can be made from sugarcane,
woodchips, crop grass
Biodiesel made by extracting and altering oil from plants. Sub for reg diesel
o Usually made form oil from soybeans and palm
o In the us govt encourages this so to reduce need for imports
Us makes most ethanol, 50 billion liters in 2012
Brazil is 2nd and uses sugarcane not corn. Only has to be replanted every 6 years, corn is every
year. Reduces fossil fuel use
Eth mixed with gas 1:9
o Has more oxygen, less air pollution
o Can make 85 : 15 too some flex fuel cars run on that
Disadvantages are reduced energy output due to weak carbon bonds ; must use more
Growing so much corn uses fossil fuels and takes up land that could be used for food
Could lead to short term food shortages
Possible net increase in co2
Switchgrass is a possibility to corn
o Can be harvested without replanting ; minimizes erosion and soil disturbance
o Doesn’t require as much fossil fuel
o BUT sugarcane and corn make more ethanol due to high sugar content
o Other stuff is high in cellulose that must be broken down into sugars
Biodiesel
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More expensive that petro diesel
80% petro and 20% diesel
Solidifies at lower temps and higher concentrations of biodiesel needs modified engines
U can modify an engine to run on vegetable oil
Most biodiesel comes from soybean or processed vegetable oil
Algae might can be used for biodiesel
o Produce more fuel per area than other crops
Emissions of co2 are lower from biodiesel than petro diesel
o Contains modern carbon as opposed to fossil carbon
Is it less? Take into consideration growing the crops
Kinetic energy of water can generate electricity
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2nd most used form of renewable energy in us
Accounts for 7% of electricity generated in us
o More than ½ comes from 3 states – Washington California Oregon
Worldwide 20% of electricity come hydro
o China leading producer followed by brazil Canada and the us
Amount of energy depends on rate of flow and vertical distance water falls or both
Run of the river system – water is retained be a dam and flows thru a channel.
o Do not store water in reservoir
o Good because very little flooding upstream, seasonal changes in river flow aren’t
affected,
o Generally small, and because they rely on natural water flow electricity generation can
be intermittent
Water impoundment system – storing water behind dam in reservoir
o By opening and closing gates, water flow can be controlled
o Most common method because you can generate electricity on demand
o Largest one in US is the Grand Coulee dam in Washington state – generates 6800 MW at
peak capacity
o Largest in world is Three Gorges Dam in Yangtze China. Capacity of 18,000 MW and can
generate 85 billion KWH per year (11% of china’s demand)
Tidal Systems – using the movement of water by gravitational pull of the moon
o Uses gates and turbines to capture kinetic energy of moving water in bays, rivers,
o Used in france, korea, and Canada
o Does not have the potential to become a major power source
o Not enough places have enough diff between high and low tide to provide sufficient
kinetic energy
o Also must have transmission lines near coast (not good)
Hydroelectricity and sustainability
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Expensive to build, but once built requires little fossil fuels to maintain
Generate large quantities of electricity without pollution, waste products and co2 emissions
Less expensive for consumer
Reservoir can provide recreational and economic opportunities
Downstream flood control
Water impoundment negative env conditions
o Free flowing river must be held back
o Resulting resevoir may destroy or flood lands
o 3 gorges dam displaced 1.3 million people and destroyed ancient architecture
o Also hurts organisms
o Large resevoirs hold more heat and contain less oxygen than free flowing rivers
 Certain parasites thrive in this water condition
o Dams also change the dynamics of the river ecosystem downstream
 Destroys sandbars
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 Changes seasonal water flow that affects salmon
Fish ladders help
 Some fish cant use them and predators hang out
Making the dam produces greenhouse gases
Production of the cement is bad (5% of global human co2 emissions)
Stuff that is flooded dies and breaks down anaerobically that releases methane pg 447
Accumulation of sediments is siltation. Lowers the amount of water held in reservoir
lower generating capacity.
Must remove siltation
Some damns are being dismantled due to env impacts