GEO-113: ENVIRONMENTAL GEOLOGY

ENERGY RESOURCES II: ALTERNATIVE SOURCES

LECTURE NOTES

Because of limited fossil fuel resources, increased demand, and environmental impacts alternative and renewable sources of energy are needed.

Some Possibilities (among others):

1. Nuclear Fission

2. Nuclear Fusion

3. Solar Energy

4. Wind Energy

5. Hydro Power

6. Tidal Energy

7. Wave Energy

8. Oceanic Heat

9. Biogas and Biomass

10. Geothermal Power

11. Hydrogen Fuel Cells

Problem with many of these is that they are not transportable ≠ utilized in large electrical power generation stations. All have pros and cons. No single ≥rightπ answer, only choices. Which one(s) we use and to what extent depends on future technological advances, economic considerations, and societal priorities.

I. Nuclear Fission

²³⁵U: (92 protons + 143 neutrons) splits to form smaller fragments ≠ forms a controlled chain reaction - releases energy, some of it in the form of heat -generates steam - turns a turbine to generate electricity. A very complex and expensive match, but they produce no air pollution.

Problems:

1. Reactor safety ≠ meltdown if cooling disrupted (≥China Syndrome≤) ≠ explosions from hydrogen gas produced during nuclear fission spreads radiation (like Chernobyl) ≠ however, so far nuclear power plants (particularly in the U.S. and Europe) are much safer than coal-fired plants. The health impacts of generating electricity are hundreds of times greater for coal than for nuclear.

2. Nuclear waste repository ≠ still have no place to store radioactive materials permanently ≠ everything stored on site in large pools of water or large sealed containers ≠ need to store high level wastes (like toxic plutonium) for tens of thousands of years isolated from the environment ≠ how do we do this? Yucca Mountain: National high-level waste repository ≠ billions of dollars to develop and will be filled within 20 years of opening (if it ever does).

3. Political issues ≠ no one wants nuclear power plants near them (NIMBY) ≠safety and terrorism concerns. No new nuclear power plants are being built in the U.S. Older ones are being shut down. By about 2050 there will be few if any left in this country.

II. Nuclear Fusion

²H (deuterium) or ³H (tritium) fuse together to make ⁴He nucleus ≠ creates a huge amount of energy, especially heat ≠ used to make electricity.

Virtually unlimited resource (hydrogen from water is the fuel) ≠ fusion products are not highly radioactive. Unfortunately do not have the technology yet where energy created greater than energy consumed, nor can we sustain reaction for any meaningful length of time ≠ may be tens or even hundreds of years before technologically feasible. Ultimately may become a very important energy resource, but not anytime soon. In the meantime, what do we do to get us to that point?

III. Solar Energy

Clean, unlimited source of energy, little or no pollution of any kind produced. Why donπt we use more of it?

Three types of solar energy:

1. Passive: heat air or thermal mass (water, concrete, stone, etc) in building - no mechanical device used in the generation of the energy - an excellent method for space heating. Can combine with appropriate building design to maximize heating in winter and cooling in summer.

2. Active: Heated medium (air, water, brine, etc.) are pumped mechanically to where they are needed - good for space and water heating.

3. Photovoltaic: Solar cells convert sunlight into electricity ≠ usually made of silicon-based material ≠ not very efficient, typically around 20 percent at best (but improving) ≠ need a whole roof covered with photovoltaic cells to generate enough electricity (about 1500 watts) to run a typical home. Can also be used in space ≠ large solar satellites in orbit produce electricity that is sent down to earth as microwaves and then converted back to electricity.

Problems:

1. A dispersed resource ≠ often need large collection areas, result in a large environmental impact ≠ often needs to be concentrated ≠ also some areas where clouds block the sun ≠ sun doesnπt shine at night ≠ requires other energy production and/or energy storage (battery) systems.

2. Technology can be expensive ≠ may cost 2 to 3 times as much as producing energy by other means ≠ however, costs are dropping.

IV. Wind Energy

Really just second-hand solar energy (unequal heating produces high and low pressure areas, creating air flow or wind) - utilized for 2000 or more years (wind mills). Produces no air pollution and is renewable.

Presently the fastest growing source of energy globally ≠ may double within 10 years ≠ still a small portion of our energy production mix (1-2 percent).

Problems:

1. Still slightly more expensive than producing energy by fossil fuels.

2. Wind doesnπt blow fast enough or often enough everywhere. However, may be very useful in specific localities (Great Plains, hill tops)

3. Dispersed ≠ need large arrays of wind turbines (wind farms). Starting to build these in remote and agricultural areas.

4. Many complaints about visual pollution and impact on migrating birds.

5. Issue of energy storage or alternative production methods when the wind is calm (same issue as solar).

V. Hydro Power

Build dams along streams to create reservoirs. Allow water to flow through dam ≠ spin a turbine ≠ spin a generator ≠ produce electricity. Produces no pollution and is totally renewable. Can also use dam and reservoir for flood control, water resource, and recreation. Seems like a win-win-win situation.

Problems:

1. Very expensive to build. Take years to complete.

2. Multiple uses are not always compatible with each other. One may want the reservoir to be full (water resource, power generation), while another may want it to be below capacity (flood control). Which use has a higher priority?

3. Destroy natural habitats and species by the flooding of the stream valley, often for tens or even hundreds of miles upstream. Towns and cities have to be abandoned or relocated.

4. Hinders or even stops fish migrations. Salmon industry in the Northwest U.S. has been nearly destroyed by the many dams along the regionπs rivers.

5. Sediment is trapped behind the dam. Silts up reservoir and prevents sediment from reaching the ocean, starving coastal beaches and increasing shoreline erosion. Big problem along west coast of the U.S.

Can also produce lesser amounts of electricity without building a dam and just using the energy of a fast flowing stream to turn the turbine. Creates much fewer environmental impacts than a typical dam.

VI. Ocean Energy

The worldπs oceans are huge reservoirs of thermal and kinetic (motion) energy. Can be utilized in a number of different ways to produce electrical energy. All are totally renewable and produced no pollution.

1) Tidal Power: Difference in elevation between high and low tides causes currents to flow. Can utilize currents to turn a turbine and generator to produce electricity on both the incoming and outgoing tides. Need at least 2-3 feet of difference between high and low tides ≠ only a relatively few places in the world were this occurs. Problems also with habitat destruction. May be applicable in specific localities.

2) Wave Energy: Use the energy of large waves to create electricity. Need waves of at least 5-10 feet in height. Doesnπt happen everywhere or all the time. May be useful in particular places where other energy sources are not available or practicable.

3) Oceanic Heat: Utilize the large difference in temperature for shallow (85∫) and very deep (35∫) waters in tropical areas. Cold water condenses a substance in a closed loop, such as ammonia, into a liquid, and the warm water turns it into a gas (like water to steam). This can then be used to turn a turbine and generator and produce electricity. Workable in only a few places, such as Hawaii, where a pilot plant is in operation.

VII. Biomass and Biogas

Also know as un-fossilized fuels. Various ways of deriving energy from organic materials:

1) Wood Burning: One of the original sources of energy for humans ≠ still used extensively in the third world. Large amounts of wood burning can create huge environmental problems, including air pollution and desertification.

2) Agriculturally Produced Fuels: includes alcohol from grains and methane from animal waste (dung can also be burned) - can be used as fuels themselves or as additives (gasohol). Can ≥grow≤ our fuels as needed ≠ takes away from food production.

3) Burn Garbage: Instead of putting garbage in landfills, burn the combustible portion of it (organically derived like paper and food waste).

All of these methods are renewable on a human time scale, but have one major drawback in common ≠ burning them produces carbon dioxide ≠ a greenhouse gas. Should be trying to reduce its emissions, not increase it.

VIII. Geothermal Power

Concentrate and extract heat from the earthπs upper crust ≠ use water as the heat extraction medium ≠ either natural or water pumped down to be heated by hot rocks. Works best in areas with high heat flow ≠ tend to regions of present volcanic and/or hydrothermal activity ≠ associated with hot spots or plate boundaries.

Two distinct types of geothermal energy: 1) Hot water (<100 degrees C ≠ no steam) used directly for space heating as in Iceland, and 2) Water and/or steam >100 degrees C ≠ convert to steam (if not already) ≠ use to turn a turbine and generator to produce electricity ≠ 40 places worldwide.

Geothermal power plants are economically competitive with other ways to make electricity and are largely (but not entirely) pollution free.

Problems

1. Extracted water and steam are often corrosive and rich in dissolved elements ≠ may clog or destroy pipes and makes disposal a problem.

2. Limited time (perhaps no more than 30-50 years) before a geothermal area cools down - not really renewable on a human scale ≠ will have to stop use and allow rocks to be reheated (100πs-1000πs years) or find a new geothermal field.

3. Limited number of suitable sites. And remember, plate boundaries have many geological hazards ≠ do you want to build a multi-billion dollar geothermal plant in an area with volcanoes and earthquakes?

IX. Hydrogen Fuel Cells

Water can be broken down into oxygen and hydrogen by passing a current through it (electrolysis). The opposite can also occur ≠ combine hydrogen and oxygen to produce electricity and water (the only thing emitted). Get oxygen from the air and hydrogen from liquid hydrogen or a hydrogen-rich fuel, such as alcohol or methane. This is the basis for all fuel cells. Have been around for decades ≠ are used on the Space Shuttle.

Can also be used as a battery. Other sources of energy are used to make electricity, which is used to split water into oxygen and hydrogen. Can be recombined to make electricity when original source of energy is unavailable or inappropriate.

Can make fuels cells for home use, for your car, and for personal electronic devices (CD player and cell phone). Technology is improving and costs are coming down. However, will have to create a hydrogen distribution system similar to what we have now for gasoline and natural gas ≠ will not happen until there is a demand ≠ will not have a demand until hydrogen is easy to get ≠ a chicken and egg situation.

The Future

How we will make energy in the future is hard to predict, but it will be different. Perhaps a variety of ways will be utilized, depending on location and what is the most appropriate source for that location. May also change from a centralized system of producing energy to a point-of-use system. Your town, neighborhood, or even you as an individual may become your own power generating company.