Junhel C. Dalanon, DMD, MAT

Alternative energy sources - renewable and ~ low impact on the environment

• Nuclear Fusion• Geothermal energy• Solar power• Hydroelectric power• Biomass• Wind energy• Hydrogen fuel

Nuclear Fusion• Combine two isotopes to make a larger one and harness the

resultant energy (similar in amount to nuclear fission).

– Main process in stars (our sun) and hydrogen bomb (uncontrolled reaction)

• The typical nuclear fusion reaction achievable on Earth is the combination of heavy Hydrogen isotopes to produce Helium:

2H + 3H (deuterium + tritium) He + neutron

+ energy (17.6 million electron volts)

However...• There has only been limited success in achieving

controlled nuclear fusion because

– Extremely high temperatures required • >100 million °C

– Reactions can be maintained over only fractions of a second

– Reaction requires more energy than the amount released

• Future technology may find a way, but it is currently not useful

Advantages - • enormous potential source

of energy (essentially unlimited, the oceans have vast amounts of deuterium)

• low environmental costs – no CO2 emissions

– non-hazardous, benign by-products = Helium

Disadvantages - • technology currently not

available...

• technology may NEVER exist...

• or may not ever be economical (e.g., requires more energy than it creates)

Geothermal Energy• Involves tapping heat generated deep in the earth, usually

due to active or dormant volcanism

• A sustainable resource as long as it is not extracted faster than it is naturally replenished.

• Need the following geologic conditions for a potentially economic source of geothermal energy:

– recent volcanic activity (magma body within 3-10 km of the surface)

– permeable aquifer

– impermeable cap rock

• Three types of power plants are used to generate power from geothermal energy:

– Dry steam plants • take steam out of fractures in the ground • and use it to directly drive a turbine that spins a generator.

– Flash plants • take hot water, usually at temperatures over 200°C, out of the ground• and allows it to boil as it rises to the surface • then separates the steam phase in steam/water separators • and then runs the steam through a turbine.

– Binary plants• the hot water flows through heat exchangers, boiling an organic fluid that spins the

turbine.

• The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat

Advantages: • Vast potential energy resource

• Simple technology

• Easy to find sources of heat

• ~ Clean resource:

– little air pollution

– few CO2 emissions

– no solid waste

Disadvantages: • Wastewater disposal is a problem

(often a saline brine - rich in toxic elements),

• Subsidence during groundwater extraction (reduced permeability in aquifer),

• Can produce earthquakes during forced injection (Rocky Mountain Arsenal)

• Rocky Mountain Arsenal– From April 1962 to November 1965, several hundred

earthquakes occurred in the Denver, CO, area

– The source of the earthquakes was traced to the Rocky Mountain Arsenal, which was manufacturing materials for chemical warfare

– Liquid waste from the manufacturing process was being pumped down a deep disposal well to a depth of about 3600 m

– The rock receiving the waste was highly fractured metamorphic rock

– Injection of the new liquid increased the fluid pressure, causing slippage along fractures

– When the injection of the waste stopped, so did the earthquakes

• Geothermal Heat Pumps– Take advantage of the stable Earth temperature of 45-58F

(7.2-14.4C) just a few feet below the surface

– GHP's circulate water or other liquids through pipes buried in a continuous loop (either horizontally or vertically) next to a building.

– Depending on the weather, the system is used for heating or cooling.

– Heating: • Earth's heat (the difference between the earth's temperature and

the colder temperature of the air) is transferred through the buried pipes into the circulating liquid and then transferred again into the building.

– Cooling: • During hot weather, the continually circulating fluid in the pipes

'picks up' heat from the building - thus helping to cool it - and transfers it into the earth

– GHP's use very little electricity and are very easy on the environment.

– In the U.S., the temperature inside over 300,000 homes, schools and offices is kept comfortable by these energy saving systems, and hundreds of thousands more are used worldwide.

– The U.S. Environmental Protection Agency has rated GHP's as among the most efficient of heating and cooling technologies

– GHP’s can be used worldwide

• Unlike other kinds of geothermal heat, shallow ground temperatures are not dependent upon tectonic plate activity or other unique geologic processes.

• Thus geothermal heat pumps can be used to help heat and cool homes anywhere

• How much geothermal energy is there?– Thousands more megawatts of power than are currently being produced could be

developed from already-identified hydrothermal resources.

– With improvements in technology, much more power will become available.

– Usable geothermal resources will not be limited to the "shallow" hydrothermal reservoirs at the crustal plate boundaries.

• Much of the world is underlain (3-6 miles down), by hot dry rock - no water, but lots of heat.

• Scientists have experimented with piping water into this deep hot rock to create more hydrothermal resources for use in geothermal power plants.

• As drilling technology improves, allowing us to drill much deeper, geothermal energy from hot dry rock could be available anywhere.

– At such time, we will be able to tap the true potential of the enormous heat resources of the earth's crust.

Solar Power• Renewable resource; many forms including:

– Direct solar energy • architectural designs use solar energy to heat and cool homes

• solar panels used to heat water to drive turbines

– heliostats

» mirrors move and track the sun

» focus rays on receiver (> 1000 °C)

– parabolic reflectors

» cylindrical reflector focuses rays on heating element

– photovoltaic (solar) cells to generate electricity

» cells contain a material that becomes unstable when struck by light

» emits electricity as the crystalline lattice reorganizes itself

» low conversion efficiency: 10-12% in silicon cells, 4-6% in cadmium/copper cells

» AND high cost per kwh

‒ Indirect solar energy - heat from solar energy drives other Earth systems which can be harnessed

1. Moving water - hydroelectric power

2. Biomass

3. Wind

Hydroelectric Power • Moving water

– tides - use energy of tidal

forces to drive turbines

• focus water flow using locks,

gates

– ocean currents and waves • difficult to concentrate

(funnels/horns) and utilize

– rivers - dams trap the water in a reservoir, force water to flow past turbines

• constructed to increase height from which water drops

• provides a constant flow of water through turbines

• 80-90% efficient in converting energy to electricity– 35-40% for fossil fuels

– 30% for nuclear fuels

• Harness energy of falling water

• Require dams to create reservoirs

• In addition to power generation, also control flooding and water supply

Biomass• Energy from organisms or their remains

– wood

– agriculture - burn or compost vegetation

– urban waste - methane gas from decay, collect and use as natural gas

– ethyl alcohol - derived from corn, added to gasoline

Wind• Harness wind energy using "wind farms" with huge

windmills

Wind-electric potential: 48 contiguous U.S. states (% of each state’s energy need). 12 states could provide ~90 % of the total U.S. energy need

• Advantages of Solar Power (both direct and indirect)

– free and renewable

– mostly pollution-free

• no CO2 emissions or other pollutants - except biomass

• Disadvantages - direct solar energy– expensive - difficult to store electricity

• cost per kilowatt hour (kwh) is 5-6 times that of other methods but costs may decrease in the future

– intermittent and localized

– construction of facilities involves semiconductor manufacture

• mining and manufacturing hazards and costs

– large arrays affect landscape aesthetics

• Disadvantages – indirect solar energy– dams cause numerous environmental problems to river

systems

• sediment pollution

• change stream velocity

• inhibit fish migrations

• large projects displace humans and animals – Three Gorges Dam, China

• dam failures result in catastrophic floods

– windmills are eyesores, noisy, and affect media reception

– wood is renewable but not necessarily sustainable as a resource

• deforestation

• desertification

• adds greenhouse gases and other forms of air pollution

Three Gorges Dam Project

• Will be the world’s largest dam

• Goals:– Power generation– Flood control– Improved navigation

Artist’s drawing of what the finished project will look like

Some facts about the Three Gorges project:• Project expected to take 17 years; completion expected in

2009.

• The Three Gorges Reservoir will inundate 632 square kilometers (395 square miles) of land.

• An estimated 1.2 million people will be resettled by the dam

• The project's 26 hydropower turbines are expected to produce 18.2 million kilowatts, up to one-ninth of China's output.

Source: Chinese government

What will it cost?• Chinese Government estimate: $25 billion

• Forced resettlement (jobs, culture, housing)

• Loss of farmland, historical sites, tourism

• Environment:– sediment pollution and erosion

• sediment-filled reservoir = no flood control capacity

– deforestation– altered ecosystem

Hydrogen Fuel

• Three attractive advantages:

– Abundant resource• mostly present in molecules combined with other elements (i.e.,

H2O, CH4)

– Combustion provides large quantities of heat

– Waste products = just water

• How is hydrogen separated?– Pass electric current through water

– Collect pure oxygen (O2) and hydrogen (H2)

– Relatively infinite supply of water, but the process does require electricity (fossil fuel? hydro? solar?)

– Usually takes more energy to separate hydrogen than you receive from it as a fuel.

• More of an energy carrier

• How could it be used as an energy resource (for example, in automobile engines)?

combustion (like gasoline)

fuel cells (hydrogen and oxygen vigorously react to produce electricity and heat) electric motor in cars

• Disadvantages:

– very dangerous, highly explosive

• needs to be highly pressurized or as a liquid

– difficult to safely store and transport

• simple technology could mean on-site manufacturing