AP Environmental Science: Renewable Energy

Renewable Energy Use in the United States

Future Fuels

Electricity Supply and Demand

Examples of Direct Solar Energy Uses

Solar space heating Photovoltaic cells Solar-trough collectors

Examples of Indirect Solar Energy Uses

Wind Water Hydrogen

Hurdles in Using Solar Energy Collection Conversion Storage Cost-

effectiveness

Direct Uses of Solar Energy: Heating = 25% U.S. Energy Budget

Direct Uses of Solar Energy - Electricity

Passive Use of Solar Energy – Space heating

75% reductionin energy bills

Trees and Energy Absorption

Significant solar energy is converted to biomass (potential energy) by photosynthesis.

Terms and Definitions: Solar Heating Systems

Active: moves water or air with pumps and blowers

Passive: moves water or air with natural convection currents or gravity

Components of Active or Passive Solar Heating Systems? Flat-plate collector Water pump Blowers Heat exchanger Improved insulation Earthen berms

Required Components? Flat-plate collector Water pump Blowers Heat exchanger Improved

insulation Earth berms

Solar hot water Solar space

heater Both

Solar Energy From the Sun Short wave

lengths (sun) are higher energy than long wavelengths (Earth)

Electromagnetic Energy Wave energy

transmits energy though the vacuum of space to the Earth.

We only “see” a small amount of it.

Solar EnergyCycle

We get 99% of the Earth’s energy from the sun through various pathways.

Photosynthesis: Solar Energy

Photosynthesis uses solar energy for the electron transport chain to change CO2 sugar/starch

USA Solar Energy Map

Some areas that have lots of cloudless sunshine could benefit greatly from solar energy units.

Solar Energy Budget

Solar energy is either reflected, absorbed in air or absorbed by the Earth.

The Hydrologic Cycle is powered by Solar Energy

The sun powers the water cycle on Earth

Solar Energy Electric Plant

Solar energy electric plants are different only in the energy source.

Solar Production of Electricity Photovoltaic cells Solar-trough

collectors Converts 22% of

incoming sunlight to electrical power at a cost of 8 cents/kwh

How Photovoltaic Cells Work

Each cell consists of two thin mylar layers.

Lower layer has atoms with single electron in outer orbit – easily lost.

Upper layer has atoms lacking one electron in outer orbit – easily accepts electrons.

How Photovoltaic Cells Work

Kinetic energy from sunlight dislodges electrons from lower layer – creates an electric potential between the two layers.

The potential provides the energy for an electrical current through the rest of the circuit.

Electrons from lower layer flow through a device back to upper side.

The Solar-trough Collector

How the Solar-trough Collector Works.

The curved reflector focuses sunlight on and heats oil in the pipe.

Heated oil used to boil water and generate steam for driving a conventional turbogenerator.

Disadvantages of Solar Energy Technologies

Expense Only works during the day Requires back-up energy sources,

e.g., Batteries Some climates not sunny enough

Hidden Costs of Traditional Energy Sources

Air pollution Strip-mining Nuclear wastes

More or Less?

The use of solar electrical power will: create ____ reliance on coal or nuclear

power. lead to significantly _____ acid rain. produce ____ electrical power for

villages in developing countries.

Electrolysis

Electrolysis (Continued)

Water is slightly acidified with a salt (eg. NaCl ) so that it is a good conductor of electricity.

Reduction of H2O to H2 occurs at cathode. 2H2O + 2e- --> 2OH- + H2 (g).

Electrolysis (Continued)

Oxidation of H20 to O2 occurs at anode. 2H2O ---> 4e- + 4H+ + O2(g).

Net cell reaction2H2O ---> 2H2(g) + O2(g).

Fuel Cells

What is the fuel in afuel cell?

Fuel Cell Mechanism

Fuel CellRunning an Electric motor Notice the

only byproduct is water.

Fuel Cells: Benefits or Limitations?

Substitute for fossil fuels Pollution factor Production technology Portability National distribution system

HydroelectricPlants

These electric generation plants use the potential energy of water

(via gravity) to run turbines to make electricity

Benefits or Drawbacks of Hydroelectric Power?

Level of pollution generated Level of environmental

degradation Amount of energy produced

Benefits or Drawbacks of Hydroelectric Power? Geographical distribution of energy

produced Ecological impacts above and below

dam Societal disruptions

Wind Power Mechanism

World Wide Wind Power

A good answer to the energy crisis.

“The answer my friend, is blowing in the wind…” Peter, Paul and Mary song.

USA Wind Power Graph

The dots show the current wind generated electricity facilities.

Benefits or Drawbacks of Wind Power Size limitations of wind turbines Megawatts of electricity produced Level of pollution generated Level of environmental degradation Geographical distribution of energy

produced Aesthetics

Examples of Bioconversion

Benefits or Drawbacks of Bioconversion Availability of the biomass resource Access to the biomass resource Public acceptance and utilization of

biomass energy Past history of human harvests within

a maximum sustained yield

Additional Renewable Energy Options OTEC (Ocean Thermal Energy

Conversion). Temperature differences between surface and 300m deep are used like nature’s heat pump.

Geothermal (Greenland) using tectonic heat to make steam.

Tidal flow used to turn generators.

Benefits or Drawbacks of Geothermal Energy

Consistent source Level of pollution Cost-effectiveness Technology required

for extraction Geographical

distribution of energy produced

Benefits or Drawbacks of Tidal Power Consistent source Level of pollution Cost-effectiveness Technology

required for extraction

Geographical distribution of energy produced

Benefits or Drawbacks of OTEC (Ocean Thermal Energy Conversion).

Temperature differences between surface and 300m deep are used like nature’s heat pump. Use ammonia as a vaporization/condensation medium.

In an average day the heat absorbed by the surface water in only one square mile is equivalent to the burning of 7000 barrels of oil.

Aspects of U.S. Energy Policy Mandates to increase fuel efficiency in cars Exploitation of public lands for fossil fuel

reserves Subsidies to producers of solar/other renewable

energy technology Research and development on alternative energy

technologies

What can a Government do?

1. Keep prices artificially low

2. Keep prices artificially high

3. Educate Consumers

Keeping prices artificially low Encourage use of sustainable/renewable

resources R&D subsidies & tax breaks to companies Enact laws that favor R&D

Keeping prices artificially high To discourage use of inefficient fuels/

technology Eliminate tax breaks & subsidies Increase gas/ fuel use taxes

Educate Consumers

Make public aware of benefits of technologybenefits of efficiencyLong range costs of environmentally harmful productsEncourage public to let company executives know about their choices

Growing Trends Shifting from supply-side (hard-path)

To demand-side (soft path) Large, centralized Macro-power

systems

To smaller, de-centalized micro-power systems