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ESC110 Chapter 12:
Energy
Outline• Solar Energy
– Photovoltaic Cells
• Fuel Cells• Energy From Biomass• Energy From Earth’s Forces
Renewable Energies:SOLAR ENERGY
• Average amount of solar energy arriving on top of the atmosphere is 1,330 watts per square meter.– Amount reaching the earth’s surface is
10,000 times more than all commercial energy used annually.• Until recently, this energy source has been too
diffuse and low intensity to capitalize for electricity.
Solar Energy
• Photosynthesis
• Passive solar heat
• Active solar heat
Solar Energy
• Passive Solar Heat - Using absorptive structures with no moving parts to gather and hold heat.– Greenhouse Design
• Active Solar Heat - Generally pump heat- absorbing medium through a collector, rather than passively collecting heat in a stationary object.
Underground massive heat storage unit
High-Temperature Solar Energy
• Mojave Desert
• Parabolic mirrors
• Two collection techniques
Average Daily Solar
Radiation
Photovoltaic Cells• During the past 25 years, efficiency of
energy capture by photovoltaic cells has increased from less than 1% of incident light to more than 10% in field conditions, and 75% in laboratory conditions.– Invention of amorphous silicon collectors
has allowed production of lightweight, cheaper cells.
Photovoltaic energy -solar energy converteddirectly to electricalcurrent
Costs for alternativeand renewable energy sources have dropped in recent years.
Storing Electrical Energy
• Electrical energy storage is difficult and expensive.– Lead-acid batteries are heavy and have
low energy density.• Typical lead-acid battery sufficient to store
electricity for an average home would cost $5,000 and weigh 3-4 tons.
– Pumped-hydro storage
– Flywheels
Promoting Renewable Energy
• Distributional Surcharges– Small charge levied on all utility customers to help
finance research and development.
• Renewable Portfolio– Mandate minimum percentage of energy from
renewable sources.
• Green Pricing– Allow utilities to profit from conservation programs and
charge premium prices for energy from renewable sources.
Renewable Energies: Fuel Cells
• Fuel cells - use ongoing electrochemical reactions to produce an electrical current
• Oxygen, hydrogen• Reformers• Efficiency
– 70% in theory– But 40-45%
Fuel Cell Electric
Car
Typical fuel cell efficiency is 40-45%.
Renewable Energies: BIOMASS
• Wood provides less than 1% of US energy, but provides up to 90% in poorer countries.– 1,500 million cubic meters of fuelwood
collected in the world annually.• Inefficient burning of wood produces smoke
laden with fine ash and soot and hazardous amounts of carbon monoxide (CO) and hydrocarbons.
– Produces few sulfur gases, and burns at lower temperature than coal.
Fuel wood Crisis in Less-Developed Countries
• About 40% of the world’s population depends on firewood and charcoal as their primary energy source.
• Supplies diminishing• Half of all wood
harvested worldwide is used as fuel.
Using Dung as Fuel
• Using dung as fuel deprives fields of nutrients and reduces crop production.
• When cow dung is burned in open fires, 90% of the potential heat and most of the nutrients are lost.
Swedish workers harvesting marsh reeds for biomass energy
Using Methane as Fuel
Anaerobic Fermentation
Alcohol from Biomass
• Ethanol - grain alcohol• Methanol - wood alcohol• Gasohol - a mixture of gasoline and
alcohol - reduced CO emissions• Ethanol production could be a solution
to grain surpluses.• Both methanol and ethanol make good
fuel for fuel cells.
Energy from the Earth’s Forces
• Water power produces 25% of the world’s electricity.
• Clean, renewable energy
• Dams - social and ecological damage
Hydropower
?
Dam Drawbacks• Human Displacement• Ecosystem Destruction• Wildlife Losses• Large-Scale Flooding Due to Dam
Failures• Sedimentation• Herbicide Contamination• Evaporative Losses• Nutrient Flow Retardation• CO2 emissions
Wind Energy
• Wind power - advantages and disadvantages
• Wind farms - potential: Great Plains, seacoasts
Wind Energy• Wind Farms - Large concentrations of
wind generators producing commercial electricity.– Negative Impacts:
• Interrupt view in remote places
• Destroy sense of isolation
• Potential bird kills
• Cannot place w/i 70 km of military airbases, etc
• Sources vary geographically
Need to know where the wind is!!
Power companies offer
customers opportunity to
purchase “Green Energy”
Geothermal Energy
Geothermal Energy
Advantages• have long life span, • no mining
needs, and • little waste
disposalpotential
Disadvantages• danger of noxious gases and • noise problems from steam valves.
Geothermal Energy in Iceland
Tidal Energy• Requires a high tide/low-tide differential of several meters
• Saltwater flooding behind the dam and heavy siltation
• Locations w/ large waves?
Ocean Thermal Electric Conversion (OTEC) Plant
An Alternative
Energy Future?
“Green Buildings”