Renewable Energy

Biomass Sources

Sources

• Solids: Wood, charcoal, manure, agricultural and timber waste, switchgrass
• Liquids (biofuels): Ethanol and biodiesel
• Gases: Methane “landfill gas” produced by breakdown of waste in landfills

Costs

Benefits

Benefits and Costs

• No net change in atmospheric carbon dioxide
• Can be produced by all nations

• Takes away land from food crops or natural habitats
• Deforestation, soil erosion, and desertification can result if plant biomass is harvested too rapidly.
• Large energy input is needed.
• Burning biomass indoors can lead to indoor air pollution.

Geothermal Energy

Geothermal

• Underground heat generated by high pressures and breakdown of radioactive elements
• Usually accessed by drilling deep below ground; steam turns turbines, generating electricity.
• Can be used directly by piping hot water from its source into homes and businesses
• Ground source heat pumps use naturally temperate soil, a few feet underground, to heat homes in winter and to cool them in summer.

Benefits

Costs

Benefits and Costs

• Causes much less air pollution than fossil fuels
• Low greenhouse gas emissions

• Not sustainable if hot groundwater is used faster than it is naturally replenished
• Hot groundwater can contain pollutants that damage machines or add to pollution.
• Some geothermal energy projects can trigger earthquakes.
• Geothermal power plants can only be built in places with easy access to geothermal energy.

Benefits and Costs

Tidal Energy

Ocean Thermal Energy

• The ocean absorbs solar energy and stores it as heat.
• Ocean thermal energy conversion (OTEC) converts heat energy in the ocean to electricity.
• Warm ocean water is used to boil liquids with very low boiling points, generating vapors that can spin turbines.
• OTEC technology is currently under development; no power plants use this method today.

OTEC

The heat content absorbed every day by tropical oceans is equivalent to the heat content of 250 million barrels of oil.

Solar Energy for Electricity

Solar Energy

• Photovoltaic cells (solar panels): Convert solar energy directly into electricity
• Concentrating solar power: Uses mirrors to focus the sun’s rays on a vessel containing fluid; creates steam to push turbines and generate electricity.

Benefits:

Costs:

Benefits and Costs

• Some pollution during manufacture
• Many regions aren’t sunny enough.
• Devices are expensive.

• Inexhaustible
• Clean—no air or water pollution produced during operation
• Low maintenance devices
• New jobs to make solar devices

Wind Energy

• Wind turbines (windmills) convert wind’s kinetic energy to electrical energy.
• Wind turbines can be placed on land or offshore.
• Turbines can be solitary or built in groups called wind farms.
• Wind speeds are 20% faster offshore than on land.

Benefits:

Costs:

Benefits and Costs

• High startup costs
• Winds can be unpredictable.
• Fastest winds are often not near population centers.
• Communities complain about the looks and noise of wind farms.
• Can be harmful to birds, bats, and butterflies

• No pollution or greenhouse gases produced during operation
• Under good wind conditions, produces far more energy than it uses
• Relatively cheap to operate

Benefits:

Costs:

Benefits and Costs

• Inexhaustible supply of hydrogen
• Few greenhouse gases or pollutants
• Water and heat might be the only byproducts.
• Can be stored and transported

• Hydrolysis (splitting of water to generate Hydrogen gas) is expensive, and breaking down methane yields carbon dioxide. Both require energy from an outside source.
• Hydrogen gas must be compressed if used for vehicle fuel.

Fuel Cells

Fuel Cells

• Hydrogen gas and Oxygen gas react to form water, producing electricity in the fuel cell’s electrodes.
• Only byproducts are water vapor and heat.
• Can power vehicles or power plants
• Can provide electricity to places “off-grid” or unreachable by conventional power companies