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 converted directly to electrical current

Costs for alternative and 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 CO 2 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

Advantages have long life span, no mining needs, and little waste disposal potential 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”