3/26/2015. Renewable Energy Alternatives. Chapter 16. Renewable energy sources. New renewables provide little energy. Alternatives to fossil fuels

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1 Chapter 16 Renewable energy sources Essential Environment: The Science Behind the Stories 4th Edition Withgott/Laposata 2012 Pearson Education, Inc. Renewable Energy Alternatives Lecture Presentations prepared by Heidi Marcum Nations are looking for ways to move away from fossil fuels while ensuring a reliable energy supply Nuclear energy is the main nonrenewable alternative Renewables include biomass and hydropower They are well established and widely used New renewables are not widely used and are still being developed to use in: Electricity, heating of air or water, fuel for vehicles Green-collar jobs: design, installation, maintenance, and management of renewable energy technologies Alternatives to fossil fuels Our global economy is powered by fossil fuels 81% of our energy comes from oil, coal, natural gas They power 2/3 of the world s electricity New renewables provide little energy Renewables are growing faster than conventional energy sources Wind power is growing at 50% per year Policy can accelerate our transition We can t switch to renewables overnight Technologic and economic barriers have been removed Remaining barriers are political Conventional sources get more government subsidies and tax breaks Policies keep fossil fuels cheap Which hurts renewables Bioenergy (biomass energy) Bioenergy: energy obtained from biomass (organic material from living or recently living organisms) Wood, charcoal, agricultural crops, manure The sustainable use of bioenergy requires careful consideration of the biomass source Over 1 billion people use wood for heat, cooking, and light 1

2 Bioenergy comes from diverse sources The diversity of bioenergy gives us many ways to use it Developing nations use wood for heating, cooking, etc. 80% of renewable energy comes from biomass Biomass is renewable only if it is not overharvested Overharvesting causes deforestation, erosion, and desertification New bioenergy sources are being developed Biopower: biomass sources are burned in power plants Generating heat and electricity Biofuels: liquid fuels used to power automobiles Biopower generates electricity Many types of biomass are combusted to generate electricity Waste products: of industries or processes Woody debris, pulp mill waste, crop residues Bioenergy crops: fast-growing willow trees, bamboo, switchgrass Combustion strategies: co-firing combines biomass and coal in a specialized boiler Gasification turn biomass to steam Pyrolysis produces a liquid fuel Benefits and drawbacks of biopower Biofuels can power automobiles Biopower increases efficiency and waste recycling It reduces CO 2 emissions Capturing landfill gas reduces methane emissions It reduces sulfur dioxide emissions when used to replace coal But burning crops deprives the soil of nutrients The soil becomes progressively depleted Ethanol: a biofuel made by fermenting carbohydrate-rich crops Is added to U.S. gasoline to reduce emissions In 2010, 13 billion gallons were made in the U.S. from corn Congressional mandates will increase ethanol production Cars can run on ethanol Flexible-fuel vehicles run on E-85 85% ethanol, 15% gasoline 9 million cars are in the U.S. Most gas stations do not yet offer this fuel Bagasse: crushed sugarcane residue used to make ethanol 50% of new Brazilian cars are flexible-fuel vehicles Ethanol may not be sustainable Environmental scientists don t like corn-based ethanol Growing corn impacts ecosystems Pesticides, fertilizers, irrigation Takes up precious land Ethanol competes with food and drives up food prices Growing corn requires energy for equipment, pesticides, fertilizers, transportation to processing plants Its EROI ratio is about 1.5:1, so it is inefficient 2

3 Biodiesel powers engines Novel biofuels are being developed Biodiesel: produced from vegetable oil, cooking grease, or animal fat Soybeans, oil palms, rapeseed Vehicles can run on 100% biodiesel B20: 20% biodiesel Biodiesel reduces emissions Its fuel economy is good It costs a bit more than gasoline Crops are specially grown Using land, deforestation Other crops can be used as biofuels Wheat, sorghum, sugar beets, hemp, grasses Algae produce lipids that can be converted to biodiesel Their carbohydrates can be fermented to make ethanol It can be grown in ponds, tanks, or photobioreactors Algae grows fast and can be harvested every few days Cellulosic ethanol: produced from structural plant material (e.g., cornstalks) that has no food value Is bioenergy carbon-neutral? In principle, biomass energy releases no net carbon Photosynthesis removes carbon that is released when biomass is burned Burning biomass is not carbon-neutral: If forests are destroyed to plant bioenergy crops If we use fossil fuel energy (tractors, fertilizers, etc.) International climate change policy does not encourage sustainable bioenergy approaches Only emissions from energy use (not land use changes) are counted toward controlling emissions Hydroelectric power (hydropower) Hydropower: uses the kinetic energy of moving water to turn turbines to generate electricity Storage technique: water stored in reservoirs behind dams passes through the dam and turns turbines Run-of-river approach generates electricity without disrupting the river s flow Water flows through a pipe then returns to the river Useful in remote areas away from electric grids Pumped-storage: water is pumped to a high reservoir and flows downward through a turbine A typical dam Hydropower is clean and renewable Hydropower has two clear advantages over fossil fuels for producing electricity: It is renewable: as long as precipitation fills rivers we can use water to turn turbines It is clean: no carbon dioxide is emitted Hydropower is efficient It has an EROI of 10:1 As high as any modern-day energy source 3

4 Hydropower has negative impacts Damming rivers destroys wildlife habitats Upstream areas are submerged Downstream areas are starved of water Natural flooding cycles or rivers are disrupted Downstream floodplains don t get nutrients Water temperatures are changed, eliminating fish species Dams block passage of fish, fragmenting the river and reducing biodiversity Hydropower may not expand much more Dams have helped many nations develop Canada, Brazil, Norway, Austria, Switzerland, etc. China s Three Gorges Dam is the world s largest dam But hydropower isn t likely to expand much more Most of the world s large rivers have already been dammed People have grown aware of the ecological impact of dams and resist more construction 98% of U.S. suitable rivers have been dammed The rest are protected Solar energy Each square meter of Earth receives 17 times the energy of a light bulb Passive solar energy: buildings are designed to maximize absorption of sunlight in winter Keep cool in summer Low, south-facing windows capture winter sun Overhangs on windows block summer light Thermal mass: materials that absorb, store, release heat in floors, roofs, and walls Vegetation protects buildings from temperature Active solar heats air and water Active solar energy collection: uses technology to focus, move, or store solar energy Flat plate solar collectors: dark-colored, heat-absorbing metal plates mounted on rooftops Water, air, or antifreeze runs through the collectors, transferring heat throughout the building Heated water is stored and used later Over 1.5 million U.S. homes and businesses heat water with solar collectors Most is for swimming pools A typical solar system for heating water Concentrating solar rays magnifies energy Power towers heat air or fluids to run a steamdriven generator Solar cookers: simple, portable ovens that use reflectors to focus sunlight onto food Concentrated solar power (CSP): technologies that concentrate solar energy to generate electricity Mirrors track the sun s movement 100 mi 2 in the Nevada desert could create enough electricity to power the entire U.S. 4

5 Photovoltaic cells generate electricity A typical photovoltaic cell Photovoltaic (PV) cells: convert sunlight directly into electrical energy The photovoltaic (photoelectric) effect: occurs when light hits the PV cell and hits a plate made of silicon Released electrons are attracted to the opposite plate Wires connecting the two plates let electrons flow Creating an electric current Small PV cells are in watches and calculators On roofs, PV cells are arranged in modules Which comprise panels gathered into arrays Variations on PV technology Solar power is growing fast Thin-film solar cells: PV materials are compressed into thin sheets Less efficient but cheaper Can be incorporated into roofing shingles, roads, etc. Producers of PV electricity can sell their power to a utility Net metering: the value of the power the consumer provides is subtracted from the monthly utility bill Feed-in tariffs pay producers more than the market price of power so power producers turn a profit Solar energy was pushed to the sidelines as fossil fuels dominated our economy Because of a lack of investment, solar energy contributes only a minuscule part of energy production But solar energy use has increased 30%/yr since 1971 Solar energy is attractive in developing nations Where hundreds of millions don t have electricity Solar energy will continue to grow China leads the world in PV cell production The U.S. may recover its leadership Due to tax credits and state initiatives Solar energy use should increase, due to: Falling prices Improved technologies Economic incentives Solar energy offers many benefits Solar technologies use no fuels, are quiet, are safe, contain no moving parts, and require little maintenance They allow local, decentralized control over power Especially helpful in developing nations In developed nations, PV owners can sell excess electricity to their local utility Green-collar jobs are being created They do not emit greenhouse gases and air pollution when up and running 5

6 Location and costs are drawbacks to solar Wind turbines turn kinetic to electric energy Not all regions are sunny enough for solar energy Daily and seasonal variation also poses problems We need storage (e.g., batteries) and backup power Solar produces the most expensive electricity But prices have dropped and efficiency has increased Wind energy: energy derived from movement of air An indirect form of solar energy Wind turbines: devices that convert wind s kinetic energy into electric energy Wind blowing into a turbine turns the blades of the rotor The nacelle contains the generator Towers are 260 feet tall Wind farms: may contain hundreds of turbines Wind is the fastest-growing energy sector Denmark leads the world in wind power Denmark gets the greatest percentage of its energy from wind power Texas generates the most wind power in the U.S. 5 nations produce 75% of the world s wind power But dozens of nations now produce wind power U.S. growth in wind power has been haphazard A long-term federal tax credit would encourage growth Global wind power has doubled every 3 years Wind power could meet 20% of the electrical needs of the entire U.S. by 2030 Offshore sites hold promise Wind power has many benefits Wind speeds are 20% greater over water than over land With less air turbulence over water Costs to erect and maintain turbines in water are higher But more power is produced and is more profitable Currently, turbines are limited to shallow water The first U.S. offshore wind farm will have 130 turbines Off Cape Cod, Massachusetts Wind produces no emissions once installed Prevents the release of CO 2, SO 2, NO x, mercury It is more efficient than conventional power sources EROI = 23:1 (nuclear = 16:1; coal = 11:1) Turbines use less water than conventional power plants Local areas can become more self-sufficient Farmers and ranchers can lease their land Produces extra revenue while still using the land Advancing technology is also reducing the cost of wind farm construction 6

7 Wind power creates job opportunities Wind power has some downsides 85,000 employees now work in the wind industry Over 100 colleges and universities offer programs and degrees that train people for jobs in renewable energy Wind power is a major source of green jobs Wind varies from time to time and place to place It can be one of several sources of electricity Batteries or hydrogen fuel can store the energy Wind sources are not always near population centers that need energy Transmission networks need to be expanded Local residents often oppose them Turbines threaten birds and bats, which are killed when they fly into rotating blades U.S. wind-generating capacity Mountainous regions have the most wind and turbines Geothermal energy Geothermal energy: thermal energy from beneath Earth s surface Radioactive decay of elements under high pressures deep inside the planet generates heat Which rises through magma, fissures, and cracks Heated groundwater erupts as geysers or submarine hydrothermal vents Hot water can directly heat building Geothermal power plants use hot water or steam to generate electricity The origins of geothermal energy The U.S. is the leader in geothermal power Geothermal energy provides more electricity than solar As much as wind 7

8 Heat pumps use temperature differences GSHPs are efficient We can take advantage of natural temperature differences between the soil and air Soil temperatures vary less than air temperatures Ground-source heat pumps (GSHPs): geothermal pumps heat buildings in the winter By transferring heat from the ground to the building In summer, heat is transferred from the building to the ground More than 600,000 U.S. homes use GSHPs GSHPs heat and cool spaces more efficiently They reduce electricity and emissions Geothermal power has benefits and limits Enhanced geothermal systems Geothermal power reduces emissions It is not sustainable if the water is withdrawn faster than it can be recharged Patterns of geothermal activity in the crust shift Dissolved salts and minerals corrode equipment and pollute the air It is limited to areas where the energy can be tapped Enhanced geothermal systems (EGS): water is put into deep holes When heated, it is withdrawn to generate electricity It could be used in many locations But EGS can trigger minor earthquakes So, our use of geothermal power will stay localized We can harness energy from the oceans Kinetic energy from the natural motion of ocean water can generate electrical power Tidal energy: dams cross the outlets of tidal basins Water is trapped behind gates Tidal currents turn turbines to generate electricity Tidal stations don t release emissions But they change the area s ecology Energy can be extracted from tidal movement Wave energy: the motion of waves is harnessed and converted from mechanical energy into electricity Many designs exist but need to be tested Ocean currents, such as the Gulf Stream, can be used Underwater turbines have been erected off of Europe 8

9 The ocean stores thermal energy A hydrogen economy Each day, tropical oceans absorb solar radiation equal to the heat content of 250 billion barrels of oil Ocean thermal energy conversion (OTEC): uses temperature differences Between the surface and deep water Warm surface water evaporates chemicals, which spin turbines to generate electricity Or, warm surface water is evaporated in a vacuum and its steam turns turbines Costs are high and no facility operates commercially yet Hydrogen fuel could store energy cleanly and efficiently By using the world s simplest and most abundant element (hydrogen) as fuel Hydrogen is an energy carrier, not an energy source Electricity produced from intermittent sources (sun, wind) would be used to produce hydrogen Fuel cells (hydrogen batteries) would use hydrogen to produce electricity to power cars, homes, computers, etc. Governments are funding research into hydrogen and fuel cell technology A typical hydrogen fuel cell A hydrogen-fueled bus Germany is one of several nations with hydrogen-fueled city buses Production of hydrogen fuel Hydrogen gas does not exist freely on Earth Energy is used to force molecules to release the hydrogen Electrolysis: electricity splits hydrogen from water 2H 2 O 2H 2 + O 2 It may cause pollution, depending on the source of electricity Hydrogen production s impact depends on the source of electricity used in electrolysis and the hydrogen source Using methane produces the greenhouse gas CO 2 CH 4 + 2H 2 O 4H 2 + CO 2 Fuel cells can produce electricity Once isolated, hydrogen gas can be used as a fuel to produce electricity within fuel cells The chemical reaction is the reverse of electrolysis 2H 2 + O 2 2H 2 O 9

10 Hydrogen and fuel cells have costs and benefits Needs massive and costly development of infrastructure Leakage of hydrogen can deplete stratospheric ozone We will never run out of hydrogen It can be clean and nontoxic to use It may produce few greenhouse gases and pollutants If kept under pressure, it is no more dangerous than gasoline in tanks Hydrogen fuel cells are up to 90% energy efficient They are silent and nonpolluting, and don t need recharging Conclusion We need to shift to renewable energy Biomass energy sources include wood and newer biofuels They can be carbon-neutral but are not strictly renewable Hydropower is a renewable, pollution-free alternative But it is nearing maximal use and can involve substantial ecological impacts Renewable sources include solar, wind, geothermal, and ocean energy sources and hydrogen fuel 10