INTRODUCTION TO ENVIRONMENTAL SCIENCES
Energy Efficiency and Non-Renewable Resources
Different countries produce their commercial energy in different ways. Developing countries rely heavily on biomass (wood, animal waste), oil, and coal. Developed countries rely heavily on oil, coal, and natural gas.
U.S. is the world's largest user of energy. It has less than 5 % of the worldıs population, but consumes 25% of the world's commercial energy, 93% of it from non-renewable sources. How we produce energy will have a huge impact on how the rest of the world produces energy and how that affects the environment.
I. Evaluating Energy: What's Good, What's Not
Our present dependence on non-renewable fossil fuels is one of the largest reasons for environmental damage, including air and water pollution, land disruption, and global warming. How do we decide which of the many other choices is better? Must do this now because of the time lag in phasing in a new energy source (25+ years).
A) Five criteria for evaluating any energy source
1. What is the sourceıs availability in near (next 15 years), intermediate (15-50 years), and long (50+ years) terms. Don't want to depend on a source that is running out. May need transitional sources until long-term sources are available.
2. What is the energy source's net energy yield? How much energy is required to produce the energy? Some energy sources are better than others. Computed as a net energy ratio (energy produced/energy expended during production). The higher this is, the better. Anything less than one operates at a net energy loss.
3. What is the cost of developing, phasing in, and using an energy source? Technology may be too expensive. This may be the case for nuclear energy.
4. What are the environmental impacts of extracting, transporting, and using an energy source? Do benefits outweigh impacts? This may be the case with coal.
5. Is the energy source renewable? Why develop it if you're just going to run out of it? Does the source make society more sustainable? This may be the case with oil.
B) Energy efficiency: Doing more with less
Most commercial energy in the U.S. is wasted (84%), either because of energy degradation during conversion (41%; can't be avoided) or because of wasteful technologies and lack of conservation (43%; avoidable). U.S. wastes as much energy as 2/3 of the world's population consumes! This amounts to $300 billion/year.
Can reduce this waste in a number of ways, including making fundamental lifestyle changes. Can also increase energy efficiency of the conversion devices we use. Can be dramatically different depending on energy source and how it is utilized. Heating a home with electricity produced in a nuclear power plant is less than 15% efficient. Converting solar energy directly to heat is 90% efficient.
Increasing energy efficiency provides numerous benefits:
1) Nonrenewable fuels will last longer.
2) Gives us more time to phase in renewable energy sources.
3) Decreases dependence on foreign sources of oil.
4) Improves national security.
5) Reduces local and global environmental damage.
6) Reduces emission of greenhouse gases.
7) Improves nation's economy and international competitiveness.
8) Could save billions of dollars and create new jobs.
Why don't we do it? Because of the availability of relatively cheap oil there is little impetus to improve efficiency. This may change as oil prices rise.
II. Improving Energy Efficiency
Can't recycle energy, but we can reduce waste. Many ways to do this depending on what segment of the economy we're talking about.
A) Reducing waste in industry
Cogeneration: Utilize more than one form of energy from the same source. Use waste heat from a coal-fired boiler to heat a building rather than letting the heat go up the stack. Widely done in Europe and more and more in the U.S. Within a decade, we could cogenerate enough energy to make nuclear power plants unnecessary.
Replace wasteful electric motors that run at constant speed (regardless of demand) with ones that run at variable speed. Switch to high-efficiency lighting and computer-controlled management systems. Turn off the lights when not needed.
B) Reducing the demand for electricity
Utilities help customers reduce their electricity demand. Known as demand-side management. Provide rebates for using energy efficient appliances and lights. Do energy audits. Provide low-interest loans to customers to increase efficiency. If the utility has to meet a lower demand, then uses less fuel and doesn't have to increase capacity by building more power plants.
C) Increasing efficiency in transportation
Most important way is to improve fuel efficiency of cars. Between 1973 and 1985 fuel efficiency doubled for new American cars and increased 37% for all cars on the road. Has improved only slightly since then (we love our SUVs!).
Current technology allows for an improvement in average fuel efficiency to 35+ mpg. Save $100 billion dollars in fuel costs, lower CO2 and other pollutant emissions, and cut oil imports in half. Some cars could exceed 100 mpg. However, until recently there has been little consumer interest in fuel-efficient cars. This is due to relatively cheap gasoline. Even at $3 a gallon, gas is not much more expensive in constant dollars than 80 years ago.
Can adjust car cost, depending on fuel efficiency. Pay a fee if a gas guzzler, receive a rebate if fuel efficient. Amount depends on mileage relative to U.S. fleet average.
Phase in more electric or hybrid cars. Electric cars produce no pollution, although the production of the electricity they use does. Also very expensive and do not have good performance characteristics. Hybrid cars use a small gasoline engine and electricity produced by that engine to power an electric motor. Which gets used depends on demand. These have fuel efficiencies of 50-100 mpg.
Switch to more efficient modes of transportation. Trains more efficient than trucks and buses more efficient than cars.
D) Saving energy in buildings
About 1/3 of commercial energy used to heat, cool, and light buildings. There are huge amounts of waste. Could reduce the typical use of energy in buildings by as much as 75-90% by applying a number of already available technologies. U.S. could reduce carbon emissions by half and save over $100 billion/year.
1) Superinsulated houses: At least R-30-40 insulation in all walls, R-60+ in roofs. Use triple-paned windows (with southern exposure). Seal all cracks and stop uncontrolled air exchange. Need heat exchangers to ventilate house. All this adds about 5-10% to the cost of a house. However, it is typically recouped within 5 years.
2) Passive solar energy: Let sunlight in during winter and block it during summer. Use overhangs on roof or awnings on windows to block summer sun but let winter sun in (trees do something similar). Use water, stone, or concrete as a thermal mass.
3) High-efficiency heating: Natural gas furnaces are 85-98% efficient. Electrical resistance heating is only 25% efficient at best. Use on-demand (tankless) water heaters rather than storing large amounts of heated (but unused) water.
4) High efficiency appliances and lights: Compact fluorescent bulbs are 4-5 times more efficient than standard incandescent bulbs. Typical home could save $1500+ over the ten-year life of the bulbs.
Tax credits and rebates could be used to foster the use of all these technologies.
III. How We Make Most of Our Energy Today
In U.S over 85% of commercial energy produced by non-renewable fossil fuels, crude oil (petroleum), natural gas, and coal. All have pros and cons to their use. Other important sources today are nuclear and hydropower. Only hydropower is renewable.
A) Oil: Source, supply, pros, and cons
Produced by the decomposition of deeply buried marine organisms. Takes millions of years to produce from source organics. Petroleum actually is a mix of many different hydrocarbon molecules, sulfur, oxygen, and nitrogen. Deposits are trapped in highly porous and permeable reservoir rocks beneath impermeable traps.
Primary recovery (simple pumping) typically gets 25% of the oil. Injecting water to push oil up the production well (secondary recovery) might net another 10-15%. Enhanced or tertiary recovery uses steam, CO2, detergents, explosives, bacteria to increase yield even more (up to 75%). Very expensive and only done if oil prices are high enough.
Oil refined into various products (solids, liquids, and gases) by distillation (separation based on molecular weight). All plastics and many synthetics come from petroleum.
Thirteen countries (OPEC) have 2/3 of the world's oil. Saudi Arabia has 1/4. U.S. has 2%, but we use 30%. Domestic production has been declining since 1980s. We are more and more dependent on foreign sources (55%). Our economy and national security is intimately tied to the price and availability of foreign oil.
World reserves will reach 80% (economic) depletion within this century. Production expected to peak about 2020. By end of century world will have used almost all easily available (cheap) oil. U.S. domestic reserves will be economically depleted within 50 years. New discoveries probably will not keep pace with increasing demand.
Oil is still relatively cheap. Easy to transport and has high net energy yield. Has led to our present oil addiction. However, there is a limited supply and prices will rise as the reserves are depleted. Huge environmental costs from its extraction, transport, processing, and use. If these costs were internalized oil would become too expensive.
B) Alternative sources of crude oil
Can produce petroleum-like liquids from oil shale and tar sand. Oil shale mined and then processed to extract kerogen (a waxy hydrocarbon), which is then processed into oil. After impurities are removed it can be refined just like petroleum.
U.S. has huge supply of oil shale. Global supplies dwarf those of conventional crude oil. However, it takes a lot of energy to mine and process (lower net energy yield), requires large amounts of water (3 barrels for every barrel produced), processed shale has larger volume than original, and large amounts of potential pollutants are left behind. Oil shale may be more trouble than it is worth.
Tar sands contain bitumen (tar-like substance), which can be processed into crude oil. Canada has a huge supply and is exploiting it. Problems are similar to oil shale.
C) Natural Gas: Source, supply, pros, and cons
Produced along with petroleum by the same geologic processes. Mostly methane (CH4; 50-90%) with the heavier gases ethane (C2H6), propane (C3H8), butane (C4H10) and H2S. Usually found above the petroleum deposit.
Methane also found unconventionally in gas hydrates on the ocean floor or in permafrost areas. May contain twice the energy as all other fossil fuel deposits combined. Problem is getting to them and environmental impacts.
Natural gas can be liquefied (LNG) for transport, as can the propane and butane (LPG). LPG stored in pressurized bottles for use where natural gas is unavailable.
Former Soviet republics have almost half the world's supply. U.S. uses almost exclusively domestic supplies. Domestic reserves will be depleted by 2100. World reserves should last slightly longer. Unconventional supplies will last 200+ years at present rates of consumption. However, if natural gas replaces oil then supplies will be exhausted quicker. Thus, it is still a rather limited resource.
Natural gas is cheaper than oil, easier to transport by pipe or ship, has a higher net energy yield, burns hotter and cleaner than oil, and produces less pollution (including CO2) when extracted and burned. Can be used directly in vehicles and fuel cells.
However, natural gas must be liquefied if transported by ship, making it highly explosive and lowering its net energy yield. Methane also is a very strong green house gas. However, a much more environmentally friendly fuel than oil and coal.
D) Coal: Source, supply, pros, and cons
Coal is a solid material derived by the decomposition of terrestrial organisms over millions of years. Goes through a series of grades with increasing energy content. The higher the grade, the more time, pressure, and temperature it takes to make.
Peat: Semi-solid, partially decayed plant material found at the surface.
Lignite (brown coal): Low sulfur content
Bituminous (soft coal): High heat content, but also high sulfur content. It is the most common type of coal.
Anthracite (hard coal): Highest heat content, lowest sulfur, and most expensive.
Most coal just has to be washed and crushed before being used. Coal is used primarily to make electricity (57% in U.S.) and steel. Not suitable for other uses such as transportation (solid) and it is no longer used in space heating.
U.S., former Soviet Union, and China have about 2/3 of world's coal supply. It is the most abundant fossil fuel. Identified world reserves should last 200+ years; unidentified reserves 500+ years at present levels of consumption. U.S reserves should last 300+ years. The why not use it more than we do?
Coal has many problems. Mining it is very dangerous and has serious health impacts on the miners. Mining coal also causes air and water pollution and land disruption. Restoration costs from surface mining can be very high. Can't be used to replace liquid or gaseous fuels unless processed. Burns dirty, requiring expensive air pollution controls. Releases radioactive particles (more than nuclear power plants) and large amounts of CO2 (more per unit of energy than any other fossil fuel). Environmental costs of coal are approximately twice that of oil and five times that of natural gas.
Can convert coal into synthetic natural gas (SNG) by coal gasification and into liquid fuels by coal liquefaction. However both processes are expensive and cut the net energy yield almost in half. Both also require huge amounts of water.
E) Nuclear energy: What happened?
Fifty years ago it was thought that thousands of nuclear power plants worldwide would produce about 1/4 of world's energy. Never happened. Now produces 6% of world's energy and this will decline with time. No new plants are planned in the U.S. Only in France and a few other European countries is nuclear power an important energy producer. Lack of development is due to high costs, frequent malfunctions, reasonable and unreasonable fears of radiation, and lack of disposal facilities.
Nuclear energy produced by a controlled nuclear fission reaction where enriched (in U235) uranium fuel rods emit neutrons and create heat. Reaction controlled by moderating control rods. Water circulates through reactor core to extract heat and keep it from melting. Heat transferred to a second system where water is converted to steam, which turns a turbine, generating electricity. Similar to a coal plant except fission is used to generate heat not combustion. However, it is a very expensive way to boil water. It is one of the most expensive ways to produce electricity.
Every 3-4 years fuel rods, which are still highly radioactive, need to be replaced. Stored "temporarily" on-site in large pools of water. Supposed to eventually be reprocessed or sent to a permanent storage facility.
Nuclear power plants last approximately 50 years before being worn out by constant radiation exposure. When decommissioned, the highly radioactive material must either be stored for thousands of years or left standing, but with no access. All present U.S. plants will probably be shut down by 2030. Cost of decommissioning them will be greater than the cost to build the plants.
Nuclear energy does have its advantages. Much less polluting than fossil fuels if operated properly. With appropriate safety features and precautions the risk of injury and death are quite low. Some estimate 6,000 premature deaths/year in U.S. compared to 100,000+ due to coal.
Catastrophic accidents are always a possibility. However, worldwide, coal burning causes the premature deaths of millions/year. Chernobyl is estimated to have caused 32,000 premature deaths; accident like that in the U.S. is very unlikely. The Three Mile Island accident in 1979 apparently killed no one, but cost $1.2 billion. Most concern about nuclear safety is in Eastern Europe and the former Soviet Union.
Biggest problem is what to do with radioactive waste. Low-level wastes need to be stored for 100-500 years. Only two low-level dump sites now operating in U.S. Used to be tossed into the ocean. High-level wastes need to be isolated for 100,000+ years. How can we guarantee that? Many ideas have been floated.
1) Deep underground burial: The favored strategy. Need to guarantee geologic stability and lack of groundwater. U.S. is trying to develop facility at Yucca Mt., Nevada. Will cost $25+ billion and is years behind schedule. France uses a salt mine.
2) Dispose in space: Rocket accident would contaminate a huge area. Not viable.
3) Bury in ice sheets: There are too many uncertainties with concept. Not viable.
4) Bury in subduction zones: Idea is unlikely given present laws and technology.
5) Deep ocean burial: Many uncertainties and banned by U.S. law.
6) Transform into less harmful isotopes: Technology unknown at present.
Given high cost of fission nuclear energy and all of the storage problems, does not seem like a viable future energy source unless costs are reduced and problems solved. Still, may be politically impossible due to public fears. So what are our other alternatives to fossil fuels and nuclear energy?