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”