Renewable Energy and Conservation Chapter 12

Direct Solar Energy I. Direct Solar Energy A. Availability: Solar energy is dispersed over the Earth’s surface, but varies in intensity depending on latitude, season, time of day and degree of cloud cover; for solar energy to be useful, we must collect it B. Cost: Although initial costs associated with converting to solar power are high, the long-term savings may offset the high start-up costs; efficiency of collecting systems is also increasing, making it a more cost effective alternative

Direct Solar Energy C. Uses: 1. Passive solar heating a.. Uses infrared radiation (waves of heat energy) to heat buildings without the need for pumps or fans to distribute the collected heat b. May utilize south-facing windows, floors of concrete or stone, and excellent insulation 2. Active solar heating a. Uses a series of collection devices mounted on a roof or in a field to gather solar energy b. Used primarily for heating water – heat absorbed is transferred to a liquid inside the panel which is then pumped to a heat exchanger, where the heat is transferred to water that will be stored in a hot water tank

Direct Solar Energy 3. Solar thermal electric generation a. Systems that collect incident sunlight and concentrate it, using mirrors or lenses, to heat a working fluid to high temperatures; water is converted to steam, which turns a turbine to generate electricity b. Usually have a backup (such as natural gas) that is available to generate electricity at night and on cloudy days c. With improved engineering, manufacturing, and construction methods, solar thermal energy may become cost-competitive with fossil fuels

Direct Solar Energy 4. Photovoltaic solar cells a. Wafers or thin films of solid state materials that are treated with certain metals in such a way that they generate electricity (a flow of electrons) when solar energy is absorbed b. Can be used on any scale – small, portable modules to large power plants c. Produce no pollution, require minimal maintenance

Direct Solar Energy d. Only about 10-15% efficient at converting solar energy to electricity, but efficiencies are improving e. Future technological progress may make PVs economically competitive with electricity produced by conventional sources

Direct Solar Energy 5. Solar-Generated Hydrogen a. Electricity generated by PVs (or any energy source) can be used to split water into oxygen and hydrogen b. Hydrogen is a clean fuel, producing very little air pollution (minimal amounts of nitrogen oxides are produced) c. Hydrogen offers a convenient way to store solar energy as chemical energy; can be easily transported by pipeline d. Hydrogen fuel cells (similar to batteries) may be used to power automobiles

Indirect Solar Energy II. Indirect Solar Energy A. Biomass 1. Consists of wood, crop wastes, and animal dung containing chemical energy that can be traced to the sun (radiant energy used by photosynthetic organisms to form the organic molecules of biomass)

Indirect Solar Energy 2. Availability: a. A renewable source of energy, as long as it is managed properly b. At least ½ of the world’s population relies on biomass as their main source of energy 3. Cost: Converting biomass to liquid fuels is expensive and overall efficiency is low

Indirect Solar Energy 4. Types: a. Combustion of wood b. Biogas – a mixture of gases produced by biomass, mostly animal waste; easy to store and transport, and burns cleanly c. Liquid fuels such as ethanol and methanol can also be produced from corn, sugar cane or even agricultural wastes and used in internal combustion engines (gasohol – alcohol mixed with gasoline)

Indirect Solar Energy 5. Advantages: a. Reduces dependence on fossil fuels b. Often makes use of wastes, reducing our waste disposal problem c. Reduced air pollution problems (as compared to fossil fuels) 6. Environmental Impact: a. Requires land and water, shifting its use from food production b. Intensive use of wood as fuel contributes to deforestation, erosion, and desertification c. Removal of crop residues for biomass fuel exposes soil to erosion and deprives the land of nutrient enrichment from decomposition

Indirect Solar Energy B. Wind Energy 1. Wind results from the warming of the atmosphere by the sun; radiant energy of the sun is transformed into mechanical energy 2. Availability: Wind is sporadic over the surface of the Earth, and varies in direction and magnitude; must be harnessed to be useful 3. Cost: As turbines have become larger and more efficient, costs for wind power have declined rapidly; currently the most cost-competitive of all forms of renewable energy 4. Mechanism: Wind turbines spin a drive shaft, powering a generator that sends electricity to nearby utilities

Indirect Solar Energy 5. Advantages: Produces no waste / emissions – a clean source of energy 6. Environmental impact: a. Birds collide with the turbines; should be located away from migratory routes b. Aesthetically displeasing; may be combined with pasture land, or located offshore to utilize ocean winds

Indirect Solar Energy C. Hydropower 1. The sun’s energy drives the hydrologic cycle; as water flows from higher elevations back to sea level, we can harness its energy 2. Availability: a. Currently, hydropower generates ~19% of the world’s electricity (9% of the US’s energy) b. Highly developed countries have already built dams at most of their potential sites, but still represents a great potential source of electricity in the developing world 3. Cost: Dams cost a great deal to build but are relatively inexpensive to operate; also have a limited lifespan (50-200 years) due to siltation of the reservoir

Indirect Solar Energy 4. Mechanism: The potential energy of water held back by a dam is converted to kinetic energy as water falls down a penstock, where it turns a turbine to generate electricity 5. Advantages: Produces no waste/emissions – a clean source of energy 6. Environmental Impact: a. Formation of a reservoir (by damming a river) destroys plant and animal habitats and displaces people b. Alteration of the river affects native fishes, especially migratory species c. Seismic activity may be induced by filling a reservoir d. Dams trap silt carried by the river, preventing nutrient-enrichment of agricultural land downstream and decreasing productivity

Indirect Solar Energy D. Ocean Waves and Temperature Gradients 1. Ocean waves are produced by winds, which are caused by the sun a. A concrete, hollow power plant box is sunk into a gulley off the coast to catch waves; as each new wave enters the chamber, the rising water in the chamber pushes air into a vent that contains a turbine, causing the turbine to spin b. More testing and improvements in design are needed before this technology can be widely implemented

Indirect Solar Energy 2. Ocean Thermal Energy Conversion (OTEC) involves the generation of electricity by using the differences in temperature at various ocean depths (temperature gradients) a. Warm surface water is pumped into a power plant where it heats a liquid (such as ammonia) to the boiling point; the ammonia steam drives a turbine to generate electricity as ammonia is cooled by the very cold water brought up from the ocean depths b. Only about 3-4% efficient, costly, and may have extreme consequences on marine ecosystems

Other Renewable Energy Sources III. Other Renewable Energy Sources A. Tidal energy 1. In areas where the difference in water level between high and low tides is great enough, it is possible to build a dam across a bay and harness this energy 2. Availability: Cannot become a significant resource worldwide because few geographical locations have a large enough difference between high and low tides 3. Cost: Very expensive to build, but relatively low operating costs

Other Renewable Energy Sources 4. Mechanism: The dam’s floodgates are opened as high tide raises the water on the bay side, then the floodgates are closed; as the tide falls, water flowing back out to the ocean over the dam’s spillway is used to turn a turbine and generate electricity 5. Advantages: No waste products / emissions; a clean source of energy 6. Environmental Impact: Building a dam across the mouth of an estuary would prevent many ocean organisms from reaching their breeding grounds

Other Renewable Energy Sources B. Geothermal Energy 1. Large, underground reservoirs of heat exist in areas of geologically recent volcanism; hydrothermal reservoirs (formed when heated groundwater is trapped by impermeable layers in the Earth’s crust) contain hot water and possibly steam

Other Renewable Energy Sources 2. Availability: a. The US is the world’s largest producer of geothermal electricity from hydrothermal reservoirs, but other countries (such as Iceland) also use this type of electricity to power many homes b. Scientists are also studying how to extract some of the geothermal energy found in hot, dry rocks of the Earth; would make this form of energy production more widely available

Other Renewable Energy Sources 3. Cost: Installation of different types of geothermal systems may be expensive, but have low operating costs and high efficiency 4. Types: a. Geothermal wells – hot fluid is brought to the surface and the resulting steam is expanded through a turbine to spin a generator, creating electricity b. Geothermal heat pumps – use an underground arrangement of pipes containing circulating fluids to extract natural heat in winter and transfer excess heat in summer

Other Renewable Energy Sources 5. Advantages: Emits a fraction of air pollutants of fossil fuel based technologies, and entails minimal land use 6. Environmental Impact: a. The water used to transfer geothermal heat to the surface is not inexhaustible – must be recirculated to ensure renewable energy b. May emit hydrogen sulfide gas

Energy Solutions: Conservation and Efficiency IV. Energy Solutions: Conservation and Efficiency A. Conservation vs. Efficiency 1. Conservation – moderating or eliminating wasteful or unnecessary energy-consuming activities Ex. carpooling, lowering driving speeds 2. Efficiency – using technology to accomplish a particular task with less energy Ex. designing and manufacturing more fuel-efficient automobiles

Energy Solutions: Conservation and Efficiency B. Energy intensity – a country’s or region’s total energy consumption divided by is GDP a. In developed countries, energy intensity is considerably higher in the US and Canada than in Japan and Europe b. Energy intensity in developing countries is substantially less than it is in industrialized countries, but the greatest increase in energy consumption is in developing nations (as countries boost their economic development, energy demands increase)

Energy Solutions: Conservation and Efficiency C. Energy-efficient technologies 1. Homes, Cars, and Industries: a. Compact fluorescent lightbulbs require 25% of the energy used by incandescent lightbulbs and last 9x longer b. “Superinsulated” homes use 70-90% less heat than those insulated by standard methods

Energy Solutions: Conservation and Efficiency C. Appliances: i) National Appliance Energy Conservation Act (NAECA) sets national appliance standards for major home appliances ii) Requires manufacturers to provide Energy Guide labels on all new appliances to provide estimates of annual operating costs

Energy Solutions: Conservation and Efficiency d. Automobile efficiency has improved dramatically as a result of the use of lighter materials and designs that reduce air drag e. New aircraft are much more fuel-efficient than older models f. Technological improvements in the paper making industry translates to increased profits for manufacturers 2. Cogeneration / Combined Heat and Power (CHP) - involves the production of two useful forms of energy from the same fuel; typically involves the generation of electricity, and then the steam produced during the process is used rather than wasted

Energy Solutions: Conservation and Efficiency 3. Commercial Buildings – energy costs usually account for ~30% of a company’s operating budget but those housed in older buildings don’t have the benefit of new technologies; energy-services companies assess how to improve energy efficiency, provide funding for improvements, then are paid by energy savings D. Electric Power Companies and Energy Efficiency 1. Demand-side Management - electric companies help consumers save energy; may offer cash awards for installation of energy-efficient technologies or may give consumers compact fluorescent lightbulbs, air conditioners, or other appliances in exchange for a slightly higher rate

Energy Solutions: Conservation and Efficiency 2. Electricity Deregulation – competitive utilities are more likely than regulated monopolies to adopt technological advances that increase energy efficiency and thereby lower costs E. Energy Conservation at the Individual Level 1. Lower thermostat in winter and raise it in summer 2. Turn off lights when you leave a room 3. Drive more slowly 4. Utilize carpooling or public transportation