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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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 7 th Ed. 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  Falling fuel prices of the 1980’s discouraged further conservation.

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Utilization Efficiencies Today’s average new home uses half the fuel required in a house built in  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 Will cut US water use by 40 trillion liters annually.

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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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 7 th Ed. 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 7 th Ed. 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 7 th Ed. 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 7 th Ed. 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 $2,000 / watt $100 / watt $5 / watt

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

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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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 7 th Ed. 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 7 th Ed. 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 7 th Ed. Fuel Cell Types Carbonite - Uses inexpensive nickel catalyst, and operates at 650 o 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 7 th Ed. 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 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 7 th Ed. 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 7 th Ed. 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 7 th Ed. 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 7 th Ed. Wood Harvest

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

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

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 7 th Ed. 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 7 th Ed. 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 7 th Ed. 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 7 th Ed. Tidal Power

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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 20 o C between warm upper layers and cooling water.

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