Chapter 22: Sustainable Energy In this chapter, the following topics will be covered:

1. Chapter 22: Sustainable Energy • In this chapter, the following topics will be covered: • Different systems for capturing solar energy • How photovoltaic collectors generate electricity • Diminishing fuelwood in less-developed countries • The use of dung, crop residues, energy crops, and peat as potential • energy sources • The use of hydropower, wind, and geothermal energy as source of • power • The use of tidal and wave energy and ocean thermal gradient as a • source of electrical energy

2. Conservation • Conservation is the best way to avoid energy shortages and • relieve environmental and health effects of our current energy technologies.

3. Utilization Efficiencies • Our current energy technologies are extremely inefficient and much • potential energy in fuels is wasted. • Many conservation techniques are simple and cost effective. • Many improvements in domestic energy efficiency have been made. • - The average home today uses half the fuel of a house built in • 1974. • - Changes include improvements in insulation, placement of • homes, window construction, etc. • More efficient industrial practices have also helped conserve energy.

5. Energy Conversion Efficiencies • Energy efficiency is a measure of energy produced compared to • energy consumed. • Net energy yield is based on the total useful energy produced during • the lifetime of an entire energy system minus the energy required to make useful energy available.

6. Table 22.1 -- Typical net efficiencies of energy-conversion devices Electric Power PlantsYield (%) Hydroelectric (best case) 90 Combined cycle-steam 90 Fuel cell (hydrogen) 80 Coal-fired generator 38 Oil-burning generator 38 Nuclear generator 30 Photovoltaic generation 10 Transportation Pipeline (gas) 90 Pipeline (liquid) 70 Waterway (no current) 65 Diesel-electric train 40 Diesel-engine automobile 35 Gas-engine automobile 30 Jet-engine airplane 10 Space heating Electric resistance 99 High-efficiency gas furnace 90 Typical gas furnace 70 Efficient wood stove 65 Typical wood stove 40 Open fireplace -10 Lighting Sodium vapor light 60 Fluorescent bulb 25 Incandescent bulb 5 Gas flame 1

7. Table 22.2 -- Typical net useful energy yields Energy Source Yield/Cost (Ratio) Nonrenewable sources Coal (space or process heat) 20/1 Natural gas (as heat source) 10/1 Gasoline and fuel oil 7/1 Coal gasification (combined cycle) 5/1 Oil shale (as liquid fuel) 1/1 Nuclear (excluding waste disposal) 2/1 Renewable sources Hydroelectric (best case) 20/1 Wind (electric generation) 2/1 Biomass methane 2/1 Solar electric (10% efficient) 1/1 Solar electric (20% efficient) 2/1

8. Negawatt Programs • Utility companies are finding it much less expensive to finance • conservation projects than to build new power plants. Rather than buy megawatts of new generating capacity, power companies are investing in "megawatts" of demand avoidance. • Cogeneration • Cogeneration is the simultaneous production of both electricity and • steam in the same plant. • By producing two types of useful energy, efficiency is increased • from 30% to 80-90%.

9. Tapping Solar Energy • A Vast Resource • The amount of solar energy reaching the earth's surface is • approximately 10,000 times all the commercial energy used each year. • However, until recently, this energy has come in a form too diffuse • and low intensity to be used except for environmental heating and photosynthesis.

11. Passive Solar Heat • Passive heat absorption is using natural materials or absorptive • structures with no moving parts to simply gather and hold heat. • A modern adaptation of this principle is the greenhouse.

14. Active Solar Heat • Active solar systems pump a heat absorbing fluid through a • small collector to gather heat. • In countries where fuels are expensive, up to 70% of domestic • hot water comes from solar collectors. • Eutectic (phase-changing) chemicals store a large amount of • energy in a small volume.

17. High-Temperature Solar Energy • Parabolic mirrors are curved reflecting surfaces that collect light • and focus it into a concentrated point. By focusing these mirrors, energy can be harnessed and used to produce power. • Parabolic mirrors are also being tested as possible devices for home • cooking in tropical areas where fuel is scarce but sunshine is plentiful. • Promoting Renewable Energy • In the United States, policies that promote energy conservation and alternative energy sources are being included in utility restructuring.

18. Photovoltaic Solar Energy • Photovoltaic cells capture solar energy and convert it directly to • electrical current. • These handcrafted single-crystal cells were too expensive for any • practical use until the recently. • Research on photovoltaic cells has dramatically increased their • efficiency, and they are now a very promising alternative source of energy.

21. Storing Electrical Energy • Electrical energy is difficult and expensive to store. • All batteries have drawbacks, from lifespan to the amount of energy • they may store. • New strategies for storing electrical energy include storing it an one • form and converting it back to electrical energy or to use it in electrolytic processes.

22. Fuel Cells • Fuel cells are devices that use ongoing electrochemical reactions to • produce an electrical current. • The fuel cell provides direct-current electricity as long as it is • supplied with hydrogen and oxygen. • A fuel cell run on pure oxygen and hydrogen produces no waste • except drinkable water and radiant heat.

23. Fuel Cell Types • Proton Exchange Membrane (PEM) is the design of fuel cell being • developed for use in automobiles. These cells are lightweight and operate at a relatively low temperature. • Phosphoric acid fuel cells are most common for stationary electrical • generation. These have higher efficiency than PEM cells but are heavier and larger. • Because they operate at very high temperatures, carbonate fuel cells • are difficult to use. • Solid oxide are the least developed of all fuel cells but have the • highest efficiency.

24. Energy from Biomass • Plants capture about 0.1% of all solar energy that reaches the earth's • surface. • The magnitude of this resource is difficult to measure. Most experts • estimate useful biomass production to be 15-20 times the amount we currently get from commercial energy sources. • Burning Biomass • Wood provides less than 1% of the energy in the United States but is • very important in less developed countries. • Inefficient burning of wood can cause a great deal of pollution. • Highly efficient and clean-burning woodstoves are available but • expensive. • Woodchips, sawdust, and other plant materials are being used in • some places in the United States andEurope as a substitute for coal and oil in industrial boilers.

25. Fuelwood Crisis in Less-Developed Countries • About 40% of the world's population depend on firewood and • charcoal as their primary energy source. • As firewood becomes scarce, more and more hours are spent • searching for fuel rather than other productive activities. • In larger cities of underdeveloped countries, fuelwood can be • ruinously expensive. • About half of all wood harvested each year world-wide is used as • fuel. • In countries where fuel is scarce, desperate people will often chop • down anything that will burn, leading to severe deforestation in some parts of the world.

27. Dung and Methane as Fuels • Where wood and other fuels are in short supply, people often dry and • burn animal manure. • This can intensify food shortages in some areas because the fertilizer • is not being returned to the soil. • Also, when burned in open fires, more than 90% of the potential heat • and most of the nutrients are lost. • Methane gas is the main component of natural gas. It is produced by • anaerobic decomposition of any moist, organic material. • Burning methane produced from manure produces more heat than • burning the dung itself, and the sludge left over can be a rich fertilizer. • Methane is a clean fuel that burns efficiently. It is produced in a low • technology, low capital process. Although this technology is well developed, its use could be much more widespread.

29. Alcohol from Biomass • Ethanol and methanol are produced by anaerobic digestion of plant • materials with high sugar content. • Gasohol is a mixture of gasoline and ethanol and burns with better • octane ratings that gasoline. • Ethanol production could be a solution to grain surpluses and bring a • higher price for grain crops than the food market offers. • Methanol burns at a lower temperature than gasoline or diesel. • Both methanol and ethanol make good fuels for fuel cells.

30. Crop Residues, Energy Crops, and Peat • Crop residues can be used as a fuel source but are expensive to • gather and are often better left on the ground as soil protection. • Some crops are grown specifically as an energy source. However, • some of these might be put to better use in other products or the cultivation of them may have negative ecological impacts. • Peat bogs are also being considered as a source of energy but • disturbing them could also have negative environmental impacts.

31. Energy from the Earth’s Forces • Winds, waves, tides, and thermal gradients are renewable energy sources that might be valuable in some areas.

32. Hydropower • Falling water has been used as an energy source since ancient times. • Water power is about 25% of total electrical generation • Currently, we use only about 10% of the available water power. • Most of the hydroelectric power produced is generated by huge • dams. Damming freeflowing rivers has many drawbacks including health risks, ecological impacts, and impedement of river traffic. • Low-head hydropower is generated by smaller dams and causes • much less of a disturbance on rivers. • Some high-efficiency turbines can operate on run of the river flow. • Micro-hydro generators are small generators able to power single • homes by being submerged in a moving current.

33. Wind Energy • Wind power has the capacity to produce 50 times the world nuclear • generating capacity. • Like solar power, wind power is a limitless resource and does little • environmental damage. • By the middle of the next century, Shell Oil suggests that half of all • the world's energy could be wind and solar generated. • Wind farms are large concentrations of wind generators producing • commercial electricity. • Wind farms do have a few problems, including bird kills and • disruption of the natural beauty.

34. Table 22.4 -- Jobs and land required for alternative energy sources Technology Land UseJobs m2 per gigawatt-hour # per terawatt-hour for 30 yearsper year ------------------------------------------------------------------------------------- Coal 3,642 116 Photovoltaic 3,237 175 Solar Thermal 3,561 248 Wind 1,335 542 -------------------------------------------------------------------------------------

35. Geothermal Energy • The earth's internal temperature can provide a useful source of • energy in some places. • Geothermal energy has been used in electric power production, • industrial processing, space heating, agriculture, and aquaculture. • Geothermal generators have a long lifespan, no mining or • transportation of fuels, and little waste disposal.

37. Tidal and Wave Energy • A tidal station works like a hydroelectric dam with spinning • turbines as water flows through them. • Environmental impacts of large scale projects to harness tidal and • wave energy are a major concern.

39. Ocean Thermal Electric Conversion • A closed-cycle ocean thermal electric conversion (OTEC) system • uses heat from sun warmed upper ocean layers to evaporate a working fluid. The pressure of the formed gas is used to spin turbines. • An open cycle system uses seawater itself as the working fluid. • OTEC systems require a temperature difference of about 20 • degrees between ocean layers to work effectively. • Disadvantages of OTEC include energy cost of pumping seawater, • saltwater corrosion of pipes and equipment, vulnerability to storms, and ecological destabilization.

41. Summary • Several sustainable energy sources could reduce or eliminate our • dependence on fossil fuels and nuclear energy. • Both ancient (water power, wind power) and exciting new • technologies (fuel cells, parabolic mirrors) are being developed as possible alternative energy sources. • Biomass may also produce some useable alternative energy sources, • but many biomass products could better be used elsewhere. • The major problem with alternative energy sources is that they are • still experimental and too expensive to be feasible sources of power. • Although conventional and alternative energy sources offer many • attractive possibilities, conservation is the least expensive and easiest solution to energy shortages.