Renewable Energy Resources & Energy Efficiency
The Importance of Improving Energy Efficiency
A. Energy efficiency is a measure of the useful energy produced compared to the energy that is converted to low-quality heat energy.
1. Energy efficiency can be achieved by using more efficient technologies that are available and are being developed. An example is the use of fluorescent bulbs (20% efficient) in place of incandescent bulbs (5% efficient).
2. About 84% of all commercial energy used in the U.S. is wasted. About 41% is wasted because of the degradation of energy quality imposed by the 2nd law of thermodynamics.
3. About 43% of the energy used is unnecessarily wasted by such things as motor vehicles, furnaces, and living and working in leaky, poorly designed buildings.
4. The U.S. unnecessarily wastes as much energy as two-thirds of the world’s population consumes.
5. When buying energy-consuming items, the life cycle cost (initial cost plus lifetime operating costs) is an important factor in making a decision.
6. Between 1970 and 2003, the U.S. has reduced the amount of energy used per person and has cut U.S. energy bills by $275 billion a year. Unnecessary energy waste still costs the U.S. about $300 billion a year.
7. Four energy devices commonly used waste large amounts of energy: the incandescent light bulb (95% waste), a nuclear power plant (86–92% waste), an internal combustion engine (75–80% waste), and a coal-burning power plant (66% waste).
B. Net energy efficiency is a measure of the useful energy we get from a resource after subtracting the energy used and wasted to make energy available.
1. Net energy efficiency includes the efficiency of each step in the process of making energy available for use.
2. A comparison of electricity produced by a nuclear power plant and passive solar heating indicates that only about 14% of the initial energy produced is useful compared to 90% for passive solar heat.
3. Two general principles for saving energy are:
a. keep the number of steps in an energy conversion process as low as possible and
b. strive to have the highest possible energy efficiency for each step in an energy conversion process.
18-2 Ways to Improve Energy Efficiency
A. Some industries save energy and money by using cogeneration, a combination of heat and power systems.
1. The same fuel source may produce both steam and electricity. About 9% of U.S. electricity is produced by cogeneration.
2. Another method is to replace energy-wasting electric motors. Most are inefficient because they run at full speed with output throttled to match the task. The cost of replacing such motors with adjustable speed drive motors would be paid back in about 1 year and save enormous amounts of energy.
3. Switch from low-efficiency incandescent lighting to higher-efficiency fluorescent lighting.
B. The best way to save energy in transportation is to increase the fuel efficiency of motor vehicles.
1. Between 1973 and 1985, fuel efficiency rose sharply for new cars sold in the U.S. This occurred because of government-mandated standards.
2. Between 1985 and 2004, the average fuel efficiency for new cars sold in the U.S. leveled off or declined slightly.
3. Fuel-efficient cars are available, but gasoline prices in the U.S. are low. Two-thirds of U.S. consumers prefer larger, more fuel inefficient vehicles, and the efficiency standards have not been raised since 1985 because of opposition from automakers and oil companies.
4. Gasoline consumption would be cut in half if Congress required the average motor vehicle to get 40 miles/gallon within 10 years, and it would save three times the oil in the U.S. current proven oil reserves and eliminate all current oil imports to the U.S. from the Middle East.
5. In 2003, China announced plans to impose stricter rules than the U.S.
C. Hybrid-electric vehicles have a battery and a small internal combustion engine to recharge the battery.
1. This vehicle runs on gas, diesel fuel, or natural gas PLUS a small battery.
2. Such cars have been available from Toyota since 1997, and Honda and Nissan since 2000.
3. Sales of hybrid vehicles are projected to grow rapidly between 2010 and 2030.
4. People buy trucks or SUVs thinking they are safer than most cars, but they are no safer due to being taller and heavier than most vehicles, which makes them more prone to roll over and harder to control in emergency stops.
D. Fuel-cell vehicles burn hydrogen fuel. The hydrogen fuel combines with oxygen in the air to produce electrical energy for power and produce water vapor.
1. Fuel cells are at least twice as efficient as internal combustion engines.
2. They have no moving parts and require little maintenance.
3. They produce little or no pollution.
4. Affordable fuel-cell vehicles should be on the market by 2020.
5. The fuel-cell car is expected to have a fuel efficiency equivalent to more than 100 mpg.
6. Hydrogen gas stations will need to be built or perhaps a fuel-cell system may be available for home use.
E. To save energy in buildings, we can get heat form the sun, super insulate the buildings, and initiate plant-covered ecoroofs.
1. Atlanta’s Georgia Power Company building uses 60% less energy than conventional office buildings of the same size.
2. Each floor extends out over the floor below it to block out the summer sun and let in the winter sun.
3. Lights focus on desks, not the entire room.
4. ING Bank in the Netherlands built an energy-efficient headquarters that cost no more than a conventional building, but uses 92% less energy.
5. The U.S. Green Building Council has certified 89 office or apartment buildings, etc. since 2001 as meeting strict environmental design standards.
6. The Green Councils Leadership in Energy and Environmental Design (LEED) program established building standards with a silver, gold, and platinum scoring system used by more and more architects, developers, and elected officials in the U.S.
7. A superinsulated house is another energy efficient design. They generally cost 5% more to build, but savings within 5 years pays this extra cost. In Sweden, these homes use 90% less energy than a typical American home.
8. Strawbale houses use walls made of compacted straw covered with plaster or adobe.
9. Ecoroofs or green roofs are covered with plants, provide good insulation, absorb storm water, outlast conventional roofs, and make a building more energy efficient.
F. We can save energy in existing buildings by insulating them, plugging leaks, and using energy-efficient heating and cooling systems, appliances, and lighting.
1. Insulate and plug leaks, since about one-third of heated air escapes through closed windows, holes, and cracks.
2. Use energy-efficient windows with low-E (low-emissivity) to cut heat losses by two-thirds and reduce CO2 emissions.
3. Stop other heating and cooling losses by wrapping ducts in attics and basements.
4. In order, these are the most energy-efficient methods to heat space:
b. a geothermal heat pump
c. passive solar heating
d. a conventional heat pump (in warm climates only)
e. a high efficiency natural gas furnace
5. Microturbines are cogeneration units about the size of a refrigerator that run on natural gas or liquified petroleum gas (LPG) to produce heat and electricity. They pay for themselves in 6–8 years in saved fuel and electricity
6. Heat water more efficiently by use of a tankless instant water heater fired by natural gas of LPG – NOT electricity. They last 3–4 times longer and cost less to operate than conventional tank heaters.
7. Use energy-efficient appliances. The Department of Energy (DOE) has set federal energy-efficiency standards for more than 20 appliances. Similar programs exist in 43 other countries. Environmental benefits are conservatively estimated at $60–80 billion.
8. Use energy-efficient lighting; it could cut electricity cost by 30–60% by using fluorescent bulbs. Brown University students in environmental studies program showed the university it could save $40,000/year by replacing incandescent bulbs in the exit signs with fluorescent ones.
9. Within 20 years we may be using even more efficient white-light LEDs (light-emitting doides) and organic LEDs. These bulbs last 80 times longer than incandescent ones.
10. Cut off electrical devices when not using them, and cut off the instant-on features in TVs, cable boxes, DVDs, computers, etc.
11. Set strict energy-efficiency standards for new buildings. This could reduce energy usage per home by about two-thirds.
G. A glut of low-cost oil and gasoline are part of the reason for energy wastage. The price does not include the harmful costs.
1. Government tax breaks and other economic incentives for consumers and businesses would help promote improving energy efficiency.
2. Invest in improving the energy efficiency of one’s home, and within a few years, the investment would be repaid and about 20% more money would be there for use.
18-3 Using Renewable Energy to Provide Heat and Electricity
A. Six types of renewable energy are solar, flowing water, wind, biomass, geothermal, and hydrogen.
1. Each of the renewable energy alternatives has advantages and disadvantages.
2. Renewable energy is not being developed because there is no financial incentive to migrate to this type of energy.
3. The prices we pay for our current energy do not include their harm to the environment and to human health.
4. In 2001, the European Union adopted non-binding agreements for its member countries to get 12% of total energy and 22% of electricity from renewable energy by 2010.
5. California gets about 12% of its electricity from renewable resources and plans to get 22% by 2010.
6. If given sufficient government R & D subsidies and tax breaks, the U.S. could get 20% of its energy from renewable resources by 2020.
7. Wind turbines operating in Kansas, North Dakota, and South Dakota, or with solar energy on a 100 square mile plot in the Nevada or southern California desert, the U.S. could get all of its electricity.
B. By orienting buildings toward the sun, passive solar heating, and by pumping a liquid, active solar heating through rooftop collectors, we can use renewable solar energy.
1. Energy-efficient windows and attached greenhouses face the sun to collect solar energy by direct gain.
2. Walls and floors (made of concrete, adobe, brick, stone, and water in containers) store collected solar energy as heat and release it slowly.
3. These systems add about 5–10% to the cost of a house, but the life cycle cost of operation is 30–40% lower.
4. Active solar heating systems absorb energy from the sun in a fluid (air, water, or antifreeze solution), which is pumped through special collectors on the roof or on racks to face the sun.
a. Some heat is used directly.
b. The rest of the heat is stored in a large insulated container filled with gravel, water, clay or a heat-absorbing chemical to be released as needed.
5. The major advantages and disadvantages are listed in Figure 18-18.
6. Most analysts do not expect widespread use of active solar collectors for home use because of high costs, maintenance requirements, and an unappealing appearance.
C. To cool houses naturally, superinsulate them and work with nature. Open windows for breezes; use fans to move air. Block sunlight with deciduous trees, window overhangs, or awnings; use a light-colored roof and hang reflecting foil in the attic.
D. Solar thermal systems can collect and transform radiant energy to high-temperature thermal energy (heat), which can be used directly or converted to electricity.
1. One type of system uses a central receiver system/power tower.
2. Heliostats/computer-controlled mirrors track and focus the sunlight on a central heat collection tower.
3. A solar thermal plant collects sunlight and focuses it on oil-filled pipes running through the middle of a large area with curved solar collectors. The sunlight produces temperatures high enough to produce steam to run turbines and produce electricity.
4. Inexpensive solar cookers can be used by individuals to concentrate sunlight and cook food. This is especially true in sunny, developing countries. They reduce indoor air pollution and deforestation and save labor and time needed to collect wood.
E. Solar cells can be used to produce electricity.
1. Photovoltaic (PV) cells/solar cells convert solar energy directly into electrical energy. The solar cell is a transparent wafer that is energized by sunlight, that causes electrons in the semiconductor to flow, creating an electrical current.
2. The solar cells can be incorporated into roof and glass walls/windows. BP is building the world’s largest factory to produce windows and cladding and roofing materials with power-producing solar cells.
3. Banks of solar cells or arrays of solar cells can be used to generate electricity.
4. Less developed countries, such as India and Zimbabwe, are installing solar-cell systems in thousands of villages.
5. Organic solar cells, incorporated into carbon-based polymers, could enter the marketplace within a few years. They could be printed on a sheet of paper and placed anywhere, such as a house, car, or even on clothing.
6. A technology in the works is a nano solar cell that can be embedded in plastic materials and manufactured in large volumes for very low cost.
7. Solar cells currently supply about 0.05% of the world’s electricity, but by 2040, they could supply one-fourth of the world’s supply.
18-4 Producing Electricity from the Water Cycle
A. Flowing water trapped behind dams and released as needed can spin turbines and produce electricity.
1. Hydropower is an indirect form of renewable solar energy.
2. Three methods are used to produce such electricity.
a. Large-scale hydropower uses a high dam across a large river to create a reservoir. The advantages and disadvantages of this method are given in Figure 18-22.
b. Small-scale hydropower uses a low dam with little or no reservoir across a small stream with the turbines turned by the stream’s flow. A micro-generator, a small turbine, can even be used to provide electricity for a single home.
c. Pumped-storage hydropower uses surplus electricity from a conventional power plant to pump water from a lower reservoir to a reservoir at higher elevation for release through a turbine when more electricity is needed.
3. Hydropower supplied 20% of the world’s electricity in 2002.
4. There is pressure on the World Bank to stop funding large-scale dams because of environmental and social consequences of them. Small-scale projects eliminate most of the harmful environmental effects of large-scale projects.
5. Electricity can also be produced by tapping into energy from tides and waves. The costs are high, and there are few favorable locations for this technology.
18-5 Producing Electricity from Wind
A. Wind power is the world’s most rapidly growing form of indirect solar energy.
1. Use of wind power increased almost seven-fold between 1995 and 2004.
2. About three-fourths of the world’s wind power is produced in Europe in inland and offshore wind farms. Denmark gets 90% of its electricity from wind.
3. The DOE points out that six Great Plains states could produce electricity from wind that would more than meet the nation’s electricity needs.
4. The advantages and disadvantages of using wind power are shown in Figure 18-24.
5. Wind power has more advantages and fewer disadvantages than any other energy resource.
6. Mass production of wind turbines would cut costs of production of electricity to become the cheapest form of energy.
18-6 Producing Energy from Biomass
A. Plant materials and animal materials can be burned to provide heat or electricity or be converted into gaseous or liquid biofuels.
1. Most biomass is burned directly for heating and cooking.
2. This comprises up to 90% of the energy used in the poorest developing countries.
3. Biomass plantations plant and harvest large amounts of fast-growing trees, shrubs, perennial grasses, and water hyacinths to produce biomass fuel.
4. Crop residues and animal manure can be converted to biofuels.
5. Ecologists argue that it makes more sense to use animal manure as a fertilizer and crop residues to feed livestock, retard soil erosion, and fertilize the soil.
6. The general advantages and disadvantages of burning solid biomass are listed in Figure 18-26.
B. Some forms of biomass can be converted into gaseous and liquid biofuels by bacteria and various chemical processes.
1. Biogas is a mixture of 60% methane and 40% CO2. 500,000 biogas digesters are used in rural China to convert plant and animal wastes to methane gas for heating and cooking with the residue then used as fertilizer.
2. Some farms in the U.S. convert waste from cattle, hogs, and chickens to biogas. The gas can be used to heat farm buildings or produce electricity.
3. About 300 large landfills in the U.S. have wells drilled in them to recover methane produce by decomposition of organic wastes. BMW’s auto plant in Spartanburg, South Carolina, obtains more than one-fourth of its electricity and one-tenth of its heat by burning methane gas from a nearby landfill.
C. There are mixed signals as to whether we can rely on ethanol and methanol as fuel.
1. Industrialized farming uses more energy to produce crops than can be obtained in the conversion of biomass, so there is a net energy loss using this form of energy.
2. Gasahol is made of gasoline mixed with pure ethanol and can be used in gasoline engines.
3. Methanol, generally made from natural gas, can be produced from carbon dioxide, coal, and biomass. One chemist George A. Olah advocates producing a methanol economy by producing methanol chemically from carbon dioxide in the atmosphere. He maintains that this will slow global warming.
18-7 Geothermal Energy
A. It is possible to tap into the geothermal energy stored in the earth’s mantle.
1. Geothermal heat pumps use a pipe and duct system to bring heat stored in underground rocks and fluids. The earth is used as a heat source in winter and a heat sink in summer.
2. Geothermal exchange or geoexchange uses buried pipes filled with fluid to move heat in or out of the ground for heating/cooling needs. The EPA declared this the most-energy-efficient, cost-effective, and environmentally clean way to heat or cool a building.
3. In deeper and more concentrated underground reservoirs of geothermal energy, we find dry steam (with no water droplets) and wet steam (steam and water droplets).
4. There is also hot water trapped in porous or fractured rock. Wells can be used to withdraw wet and dry steam as well as hot water for heat or to produce electricity.
5. Three other nearly nondepletable sources of geothermal energy are molten rock (magma), hot dry-rock zones, and warm-rock reservoir deposits.
6. About 85% of Iceland’s buildings and 45% of its energy is provided by geothermal energy.
7. The advantages and disadvantages of geothermal energy are listed in Figure 18-29.
8. Two problems with goethermal energy are that it is too expensive to tap except for the most concentrated and accessible sources and it may be depleted if heat is removed faster than it can be renewed.
A. Hydrogen gas can be produced from water and organic molecules and produces nonpolluting water vapor when burned.
1. It could be ready to be phased in by 2020–2030.
2. There are three problems with widespread use of hydrogen as fuel.
a. Hydrogen is chemically locked up in water and organic compounds.
b. It takes energy and money to produce hydrogen from water and organic compounds. It is not a source of energy; it is a fuel produced by using energy.
c. Current versions of fuel cells are expensive, but are the best way to use hydrogen to produce electricity.
3. The advantages and disadvantages of using hydrogen for fuel are given in Figure 18-30.
4. Difficulties with using hydrogen include lack of free hydrogen and a need to use other energy sources to produce hydrogen.
5. It may be possible to produce hydrogen by growing bacteria and algae that will produce hydrogen gas rather than oxygen as a byproduct.
6. Possible ways to store hydrogen once it is produced include:
a. Store it in compressed gas tanks either above or below ground.
b. Store it as more dense liquid hydrogen, but then must be kept very cold and this is costly.
c. Store it in solid metal hydride compounds. DaimlerChrysler developed sodium borohydride that is safe to pump in and out of a vehicle safely and cleanly.
d. Absorb hydrogen gas on activated charcoal or graphite nanofibers.
e. Trap and store hydrogen gas in a framework of water molecules called clathrate hydrates.
7. Hydrogen may be safer than gasoline because it disperses into the atmosphere quickly. It does not pose a fire hazard, and metal hydrides, charcoal powders, and graphite carriers will not explode or burn if a vehicle’s tank ruptures.
B. Widespread use of hydrogen may decrease the protective ozone in the stratosphere over Antarctica for a few months each year.
1. The problem may not be as serious as originally projected because:
a. the model is based on poorly understood atmospheric chemical interactions,
b. the assumptions about leakage of hydrogen may be much too high due to improved technologies, and
c. global efforts are in place to drastically reduce ozone depletion by 2050, and widespread use of hydrogen is not expected until after 2050.
C. We need to focus on the immediate priorities of sharply reducing greenhouse gas emissions by increasing fuel efficiency and use of renewable energy.
1. We need to concentrate on reducing dependence on fossil fuels and concentrate on reducing CO2 emissions to help slow global warming.
2. We need to greatly improve fuel-efficiency standards for motor vehicles.
3. We need to provide large tax breaks for people and businesses that use fuel-efficient cars, buildings, heating systems, and appliances.
4. We need to invest more in public transportation that runs on less polluting natural gas.
5. We need to increase research and development subsidies for development and phasing in of renewable energy technologies.
6. We need to provide very large tax breaks for those using renewable-energy technologies for a period of at least 25 years.
18-9 Entering the Age of Decentralized Micropower
A. The era of large centralized power plants is coming to a close. Decentralized systems called micropower systems that generate 1–10,000 kilowatts of power are the future.
B. Advantages and disadvantages of the decentralized micropower systems over traditional systems are given in Figure 18-33.
18-10 A Sustainable Energy Strategy
A. Government use of a combination of subsidies, tax breaks, and taxes can be used to promote or dampen use of various energy alternatives.
B. Economics and politics are the two basic strategies to help stimulate or dampen use of a particular resource.
1. Several strategies include:
a. Keep energy prices artificially low to encourage use of selected energy resources. Our current system actually encourages energy waste.
b. Keep energy prices artificially high to discourage use of a resource.
c. Increase taxes on fossil fuels to reduce air and water pollution and slow greenhouse gas emissions, and encourage improvements in energy efficiency with greater use of renewable energy resources.
C. To develop a more sustainable energy future, we must stop the waste, use the sun, and cut pollution.
1. The U.S. is described as a first world nation with a third world electrical grid system.
2. Implementing policies described in Figure 18-35 over the next several decades would save money, create a net gain in jobs, reduce greenhouse emissions, and sharply reduce air and water pollution. They might also increase national security by reducing dependence on imported oil and decrease dependence on large, centralized coal and nuclear power plants.
1. The advantages of improving energy efficiency include benefits to the environment, people, and the economy through prolonged fossil fuel supplies, reduced oil imports, very high net energy yield, low cost reduction of pollution, and improved local economies.
2. The advantages of solar energy include reduction of air pollution, reduction of dependence on oil, and low land use. Disadvantages include that production of photocells results in release of toxic chemicals, the life of systems is short, they can damage deserts, they need backup systems, and they have a high cost.
3. The advantages of hydropower include that it has a high net energy yield, is a low cost electricity, has a long life span, has no carbon dioxide emissions during operation, has food control below the dam, provides water for irrigation, and increases reservoir development. Disadvantages include a high construction cost, high environmental impact, high carbon dioxide emissions from biomass decay, flooding of natural areas, conversion of land habitats to lake habitats, danger of the dam collapsing, people relocation, limits fish populations below the dam, and decreases flow of silt.
4. The advantages of wind power include a high net energy yield and efficiency, a low cost and environmental impact, no carbon dioxide emissions, and quick construction. Disadvantages include a need for winds and backup systems, high land use, visual and noise pollution, interfering with bird migrations, and causing the death of birds of prey.
5. The advantages of biomass include large potential supplies, moderate costs, no net carbon increase, and makes use of agricultural, timber, and urban wastes. Disadvantages include being a nonrenewable resource, having a moderate to high environmental impact, its low photosynthetic efficiency, and causing soil erosion, water pollution, and loss of wildlife.
6. The advantages of geothermal energy include a very high efficiency, low carbon dioxide emissions, low cost and land use, low land disturbance, and moderate environmental impact. Disadvantages include that suitable sites are scarce, there is potential depletion, it has moderate to high air pollution, noise, and odor, and it has a high cost.
7. The advantages of hydrogen gas include the fact that it can be produced from water, the low environmental impact, no carbon dioxide emissions, a competitive price, ease of storage, safety, and high efficiency. Disadvantages include the energy needed to produce the fuel, a negative energy yield, being nonrenewable, high cost, and no fuel distribution systems exist.
8. The advantages of using smaller, decentralized micropower sources include size, fast production and installation, high energy efficiency, low or no CO2 emissions, low air pollution, easy repair, reliability, increased national security, and being easily financed.
9. We can improve energy efficiency by increasing fuel efficiency standards, large tax credits for purchasing energy efficient cars, houses, and appliances, encouraging independent energy production, and increasing research and development.