Sustainable Energy

1. Sustainable Energy Chapter 22 Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

2. Outline: • Conservation • Cogeneration • Tapping Solar Energy • Passive vs. Active • High Temperature Solar Energy • Photovoltaic Cells • Fuel Cells • Energy From Biomass • Energy From Earth’s Forces Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

3. CONSERVATION • Utilization Efficiencies • Most potential energy in fuel is lost as waste heat. • In response to 1970’s oil prices, average US automobile gas-mileage increased from 13 mpg in 1975 to 28.8 mpg in 1988. • Falling fuel prices of the 1980’s discouraged further conservation. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

4. Utilization Efficiencies • Today’s average new home uses half the fuel required in a house built in 1974. • Reducing air infiltration is usually the cheapest, quickest, and most effective way of saving household energy. • According to new national standards: • New washing machines will have to use 35% less water in 2007. • Will cut US water use by 40 trillion liters annually. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

5. Energy Conversion Efficiencies • Energy Efficiency is a measure of energy produced compared to energy consumed. • Thermal conversion machines can turn no more than 40% of energy in primary fuel into electricity or mechanical power due to waste heat. • Fuel cells can theoretically approach 80% efficiency using hydrogen or methane. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

6. Energy Conversion Efficiencies • Net Energy Yield - Based on total useful energy produced during the lifetime of an entire energy system, minus the energy required to make useful energy available. • Expressed as ratio between output of useful energy and energy costs. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

7. Negawatt Programs • It is much less expensive to finance conservation projects than to build new power plants. • Power companies investing in negawatts of demand avoidance. • Conservation costs on average $350/kw • Nuclear Power Plant: $3,000 - $8,000/kw • Coal Power Plant: $1,000/kw Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

8. Cogeneration • Cogeneration - Simultaneous production of both electricity and steam, or hot water, in the same plant. • Increases net energy yield from 30-35% to 80-90%. • In 1900, half of electricity generated in US came from plants also providing industrial steam or district heating. • By 1970’s cogeneration had fallen to less than 5% of power supplies. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

9. TAPPING SOLAR ENERGY • A Vast Resource • Average amount of solar energy arriving on top of the atmosphere is 1,330 watts per square meter. • Amount reaching the earth’s surface is 10,000 times more than all commercial energy used annually. • Until recently, this energy source has been too diffuse and low intensity to capitalize for electricity. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

10. Average Daily Solar Radiation Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

11. Solar Energy • Passive Solar Heat - Using absorptive structures with no moving parts to gather and hold heat. • Greenhouse Design • Active Solar Heat - Generally pump heat- absorbing medium through a collector, rather than passively collecting heat in a stationary object. • Water heating consumes 15% of US domestic energy budget. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

12. Solar Energy • Eutectic Chemicals are also used to store large amounts of energy in a small volume. • Heating melts the chemicals and cooling returns them to a solid state. • Most do not swell when they solidify and undergo phase changes at higher temperatures than water and ice. • More convenient for heat storage. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

13. HIGH TEMPERATURE SOLAR ENERGY • Parabolic mirrors are curved reflective surfaces that collect light and focus it onto a concentrated point. Two techniques: • Long curved mirrors focused on a central tube containing a heat-absorbing fluid. • Small mirrors arranged in concentric rings around a tall central tower track the sun and focus light on a heat absorber on top of the tower where molten salt is heated to drive a steam-turbine electric generator. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

14. Promoting Renewable Energy • Proposed Energy Conservation Policies: • Distributional Surcharges • Small fee levied on all utility customers. • Renewable Portfolio • Suppliers must get minimum percentage of power from renewable sources. • Green Pricing • Allows utilities to profit from conservation programs and charge premium prices for renewable energy. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

15. Photovoltaic Solar Energy • Photovoltaic cells capture solar energy and convert it directly to electrical current by separating electrons from parent atoms and accelerating them across a one-way electrostatic barrier. • Bell Laboratories - 1954 • 1958 - $2,000 / watt • 1970 - $100 / watt • 2001 - $5 / watt Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

16. Energy Costs Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

17. Photovoltaic Cells • During the past 25 years, efficiency of energy capture by photovoltaic cells has increased from less than 1% of incident light to more than 10% in field conditions. • Invention of amorphous silicon collectors has allowed production of lightweight, cheaper cells. • Currently $100 million annual market. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

18. Storing Electrical Energy • Electrical energy storage is difficult and expensive. • Lead-acid batteries are heavy and have low energy density. • Metal-gas batteries are inexpensive and have high energy densities, but short lives. • Alkali-metal batteries have high storage capacity, but are more expensive. • Lithium batteries have very long lives, and store large amounts of energy, but are very expensive. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

19. FUEL CELLS • Fuel Cells - Use on-going electrochemical reactions to produce electric current. • Positive electrode (cathode) and negative electrode (anode) separated by electrolyte which allows charged atoms to pass, but is impermeable to electrons. • Electrons pass through external circuit, and generate electrical current. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

20. Fuel Cells Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

21. Fuel Cells • Fuel cells provide direct-current electricity as long as supplied with hydrogen and oxygen. • Hydrogen can be supplied as pure gas, or a reformer can be used to strip hydrogen from other fuels. • Fuel cells run on pure oxygen and hydrogen produce no waste products except drinkable water and radiant heat. • Reformer releases some pollutants, but far below conventional fuel levels. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

22. Fuel Cells • Typical fuel cell efficiency is 40-45%. • Current is proportional to the size of the electrodes, while voltage is limited to about 1.23 volts/cell. • Fuel cells can be stacked together until the desired power level is achieved. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

23. Fuel Cell Types • Proton Exchange Membrane - Design being developed for use in automobiles. • Lightweight and operate at low temps. • Efficiency typically less than 40%. • Phosphoric Acid - Most common fuel design for stationary electrical generation. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

24. Fuel Cell Types • Carbonite - Uses inexpensive nickel catalyst, and operates at 650o C. • Good heat cogeneration, but difficult to operate due to the extreme heat. • Solid Oxide - Uses coated zirconium ceramic as electrolyte. • High operating temperatures, but highest efficiency of any design. • Still in experimental stage. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

25. ENERGY FROM BIOMASS • Plants capture about 0.1% of all solar energy that reaches the earth’s surface. • About half the energy used in metabolism. • Useful biomass production estimated at 15 - 20 times the amount currently obtained from all commercial energy sources. • Renewable energy resources account for 18% of total world energy use, and biomass makes of three-quarters of that supply. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

26. Burning Biomass • Wood provides less than 1% of US energy, but provides up to 95% in poorer countries. • 1,500 million cubic meters of fuelwood collected in the world annually. • Inefficient burning of wood produces smoke laden with fine ash and soot and hazardous amounts of carbon monoxide (CO) and hydrocarbons. • Produces few sulfur gases, and burns at lower temperature than coal. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

27. Fuelwood Crisis • About 40% of world population depends on firewood and charcoal as their primary energy source. • Of these, three-quarters do not have an adequate supply. • Problem intensifies as less developed countries continue to grow. • For urban dwellers, the opportunity to scavenge wood is generally nonexistent. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

28. Fuelwood Crisis • Currently, about half of worldwide annual wood harvest is used as fuel. • Eighty-five percent of fuelwood harvested in developing countries. • By 2025, worldwide demand for fuelwood is expected to be twice current harvest rates while supplies will have remained relatively static. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

29. Wood Harvest Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

30. Dung • Where other fuel is in short supply, people often dry and burn animal dung. • Not returning animal dung to land as fertilizer reduces crop production and food supplies. • When burned in open fires, 90% of potential heat and most of the nutrients are lost. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

31. Methane • Methane is main component of natural gas. • Produced by anaerobic decomposition. • Burning methane produced from manure provides more heat than burning dung itself, and left-over sludge from bacterial digestion is a nutrient-rich fertilizer. • Methane is clean, efficient fuel. • Municipal landfills contribute as much as 20% of annual output of methane to the atmosphere. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

32. Anaerobic Fermentation Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

33. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

34. Wind Energy • Estimated 20 million MW of wind power could be commercially tapped worldwide. • Fifty times current nuclear generation. • Typically operate at 35% efficiency under field conditions. • When conditions are favorable (min. 24 km/hr) electric prices typically run as low as 3 cents / KWH. • Standard modern turbine uses only two or three blades in order to operate better at high wind speeds. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

35. Wind Energy • Wind Farms - Large concentrations of wind generators producing commercial electricity. • Negative Impacts: • Interrupt view in remote places • Destroy sense of isolation • Potential bird kills Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

36. Geothermal Energy • High-pressure, high-temperature steam fields exist below the earth’s surface. • Recently, geothermal energy has been used in electric power production, industrial processing, space heating, agriculture, and aquaculture. • Have long life span, no mining needs, and little waste disposal. • Potential danger of noxious gases and noise problems from steam valves. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

37. Tidal and Wave Energy • Ocean tides and waves contain enormous amounts of energy that can be harnessed. • Tidal Station - Tide flows through turbines, creating electricity. • Requires a high tide / low-tide differential of several meters. • Main worries are saltwater flooding behind the dam and heavy siltation. • Stormy coasts with strongest waves are often far from major population centers. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

38. Tidal Power Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

39. Ocean Thermal Electric Conversion • Heat from sun-warmed upper ocean layers is used to evaporate a working fluid, such as ammonia, which has a low boiling point. • Gas pressure spins electrical turbines. • Need temperature differential of about 20o C between warm upper layers and cooling water. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

40. Summary: • Conservation • Cogeneration • Tapping Solar Energy • Passive vs. Active • High Temperature Solar Energy • Photovoltaic Cells • Fuel Cells • Energy From Biomass • Energy From Earth’s Forces Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.