Ch. 10: Renewable Resources

4. Wind Energy

- For centuries, wind has been used to move ships, grind grains, pump water, and do other forms of work. In more recent times, wind has been used to generate electricity - Although places such as the Dakotas have the strongest winds, they are remote from energy-using population centers, and large losses in the amount of electricity would occur as it is transmitted through electric lines - Because winds are variable, so is the amount of energy generated by each wind turbine. This means that electrical energy from wind must be coupled with other, more reliable sources of energy. - Accounts for less than 1% of the total worldwide energy consumption

a. Conventional electric generation

- To produce electricity using a turbine, the energy from the sun must be collected and concentrated to heat water to make steam. - There are basically two designs used: 1. One design, called a solar power tower, uses mirrors to focus sunlight at a central point that raises the temperature and allows for the production of steam. 2. Parabolic Trough. Most successful. can heat oil in pipes to about 400˚C (750˚F). This heat can be transferred to water, which is turned into steam that is used to run conventional electricity-generating turbines

Major Kinds of Renewable Energy

1. Biomass Conversion 2. Hydroelectric Power 3. Solar Energy 4. Wind Energy 5. Geothermal Energy 6. Tidal Power

Biomass- Environmental Issues

1. Habitat and biodiversity loss 2. Air pollution 3. Carbon dioxide and climate change 4. Effects on food production

What percent of world energy comes from renewable energy sources?

13% of the world's energy comes from renewable energy

Biomass Conversion Technologies

In order to use biomass as a source of energy, it must be burned. Often it is important to convert the biomass into a different form that is easier to transport and use. There are several technologies capable of making the energy of biomass available for use. These include direct combustion and cogeneration, ethanol production, anaerobic digestion, and pyrolysis.

List industries that typically make use of the waste they produce to provide themselves with energy.

Lumber, paper mills, and sugar cane processing plants are industries that make use of their waste by burning it.

Solar Energy- Environmental Issues

Since solar energy is renewable, it has minimal environmental impact. However, the manufacture of the silicon or other materials that make up the units requires large amounts of energy. Thermal or photovoltaic power plants require large amounts of land to position their mirrors or solar collectors. The SEGS system in California covers 6.4 km2 (2.5 mi2). The installation of photovoltaics or water heating systems on buildings does not require additional space and is often incorporated into the design of the building.

Potential for Additional Hydropower

Some areas of the world, such as Canada, the United States, Europe, and Japan, have already developed about 50 percent of their hydroelectric potential. Most of the potential for development of new hydroelectric power facilities is in Africa, Asia, South America, Eastern Europe, and Russia.

List three negative environmental impacts of using biomass to provide energy.

The negative environmental impacts of biomass are loss of habitat, air pollution, release of carbon dioxide, and decrease in food production.

Wind Energy- Environmental Issues

Wind generators do have some negative effects. The moving blades are a hazard to birds and bats. Newer wind turbines, however, have slower-moving rotors that many birds such as the golden eagle find easier to avoid. In addition, some people consider the sight of a large number of wind generators to be visual pollution.

What are negative environmental impacts of developing hydroelectric power

Large amounts of lands are flooded, dams hinder the migration of fish, and change water quality up and down stream.

How is the biofuel ethanol produced?

Ethanol is produced by fermenting sugars in plants such as corn or sugar cane.

Biomass- Carbon dioxide and climate change

- A consensus exists among scientists that biomass fuels and wastes used in a sustainable manner result in no net increase in atmospheric carbon dioxide. - This is based on the assumption that all the carbon dioxide given off by the use of biomass fuels was taken from the atmosphere during photosynthesis. Increased substitution of biomass fuels for fossil fuels would reduce carbon dioxide emissions and the effects of climate change.

What renewable energy source provides the majority of renewable energy?

Biomass provides the majority of global renewable energy

Does Corn Ethanol Fuel Make Sense?

Since ethanol only contains 67.2 percent and E85 only contains 72 percent of the energy of gasoline, they must cost less than gasoline to be competitive. Thus, in order for E85 to be more economical than regular gasoline, its cost must only be 72 percent of the price of gasoline. In other words, it must cost 28 percent less than regular gasoline. Although E85 costs less than regular gasoline, it does not cost 28 percent less, and thus it is more expensive to use than regular gasoline.

Describe two different ways sunlight is used to make electricity.

Sunlight can be used to create steam that turns turbines and generates energy or photovoltaic cells can generate energy by capturing sunlight.

List two reasons people oppose additional wind energy development.

Sunlight can be used to create steam that turns turbines and generates energy or photovoltaic cells can generate energy by capturing sunlight.

Why is burning of municipal waste to produce energy more common in Europe than in North America?

The burning of municipal waste is more common in Europe than in North America because Europe has strict restrictions on land used for landfills.

The Status of Renewable Energy

- Since fossil fuels are nonrenewable, as they become scarce the price rises - As the price of fossil fuels increases, many forms of renewable energy become economically viable - A third factor is the concern about climate change, which is driven by carbon dioxide emissions, primarily from the burning of fossil fuels. In general, renewable energy sources do not add to carbon dioxide emissions.

b. Waste

- Wastes of various kinds are a major source of biomass and other burnable materials produced by society. - Certain industries, such as lumber mills, paper mills, and plants that process sugar from sugarcane, use biomass as a raw material for their products and in the process produce wastes such as sawdust, wood scrap, waste paper, or bagasse (sugarcane stalks), which are burnable. - These industries typically burn these wastes to provide energy for their operations. - Municipal solid waste is also burnable. - However, to use municipal solid waste to produce energy requires that the waste be sorted to separate the burnable organic material from the inorganic material. - although energy from solid waste is expensive, one can deduct the avoided landfill costs from the cost of producing energy from waste. Where landfill costs are high, municipal waste-to-energy plants make economic sense - Plastics, textiles, rubber, and similar materials contribute the rest of the burnable portion of trash. - In the United States, about 11 percent of solid waste is burned in 86 plants, resulting in about 2,700 megawatts of electricity. - Europe and Japan have much less available land and have placed restrictions on landfills. Thus, these countries have a much higher rate of burning of solid waste. - Countries in Western Europe have over 400 waste-to-energy plants. - Japan burns about 80 percent of its waste, and Germany burns nearly all of its waste that is not recyclable.

5. Geothermal Energy

- obtained in two different ways. In geologically active areas where hot magma approaches the surface, the heat from the underlying rock can be used to heat water. The heated water can then be used directly either to heat buildings or to generate electricity by way of a steam turbine - The United States produces about 30 percent of the world's geothermally generated electricity. - Other countries that produce significant amounts of geothermal electricity are the Philippines, Italy, Mexico, Japan, New Zealand, Indonesia, and Iceland. - It is also possible to use heat pumps to obtain geothermal energy from areas that are not geologically active. All objects contain heat energy, which can be extracted from and transferred to other locations. Geothermal heat pump systems use a closed loop of underground pipes. A water-antifreeze solution is circulated through the pipes, and heat is extracted from the solution and transferred to the building in the same way a refrigerator moves heat from the inside to the outside. Typically the amount of heat energy harvested is three to four times the amount of electrical energy used to run the system.

Active Solar Systems

- requires a solar collector (usually a flat plate collector), a pump, and a system of pipes to transfer the heat from the site where it is captured to the area to be heated. - most commonly used to provide heat energy for water heaters, pools, and homes. - Because sunlight is intermittent, active solar heating systems require heat storage mechanisms and usually also require conventional energy sources to provide energy when solar energy is inadequate. Rock, water, or specially produced products are used to store heat during the day, and the storage medium releases heat when the sun is not shining. - Makes economic sense if it can offset considerable amounts of heating energy from conventional systems over the life of the building or the system.

Direct combustion

The most common way that biomass and waste are used for energy production is by burning them to produce heat or electricity. In much of the developing world, the primary use of energy derived from biomass is as fires to provide heat for space heating and cooking. if a biomass-fired power plant can be used to provide both heat and electricity (cogeneration system), the economics and energy efficiency improve significantly.

Geothermal Energy- Environmental Issues

The use of geothermal energy from geologically active areas creates some environmental problems. The steam often contains hydrogen sulfide gas, which has the odor of rotten eggs and is an unpleasant form of air pollution. (The sulfides from geothermal sources can be removed.) The minerals in the steam corrode pipes and equipment, causing maintenance problems. The minerals are also toxic to fish if wastewater is discharged into local bodies of water.

Hydropower- Environmental Issues

- Although hydroelectric power is a renewable energy source and does not emit air or water pollutants, there are still environmental consequences associated with developing hydroelectric facilities. The most obvious impact of hydroelectric dams is the flooding of vast areas of land, much of it previously forested or used for agriculture. - The construction of the Three Gorges Dam in China inundated 153 towns and 4,500 villages and caused the displacement of over a million people. In addition, numerous archeological sites were submerged and the nature of the scenic canyons of the Three Gorges was changed. - Dams and reservoirs also greatly alter watersheds. - Damming a river alters the normal flow of the river and changes the quality of water (temperature, amount of particulate matter, oxygen content, etc.) in the river downstream of the dam. - Dams also alter the migration patterns of fish and often prevent fish from migrating upstream to spawn. - These impacts can be reduced by requiring that dams release enough water to maintain minimum flows downstream of a dam and by creating fish ladders that allow fish to move upstream past the dam. - Silt, normally carried downstream to the lower reaches of a river, is trapped by a dam and deposited on the bed of the reservoir. - This silt slowly fills a reservoir, decreasing the amount of water that can be stored and used for electrical generation. The river downstream of the dam is also deprived of silt, which normally fertilizes the river's floodplain during high-water periods. - The flooded area behind a new dam contains vegetation that decomposes. The bacteria involved in decomposition have two negative effects. - They release carbon dioxide and some of them can convert mercury that is naturally in the soil into methylmercury that can accumulate in fish. This poses a health hazard to those who depend on these fish for food. It is thought that both of these problems are temporary and will be reduced once the flooded vegetation is decomposed.

Biomass Fuels and the Developing World

- Although most of the world uses fossil fuels as energy sources, much of the developing world relies on biomass as its source of energy. The biomass can be wood, grass, agricultural waste, or dung. - This dependence on biomass has several major impacts: 1. Often women and children must walk long distances and spend long hours collecting firewood and transporting it to their homes. 2. Because the fuel is burned in open fires or inefficient stoves, smoke contaminates homes and affects the health of the people. The World Health Organization estimates that in the developing world, 40 percent of acute respiratory infections are associated with poor indoor air quality related to burning biomass. A majority of those who become ill are women and children because the children are in homes with their mothers who spend time cooking food for their families. 3. Often the fuel is harvested unsustainably. Thus, the need for an inexpensive source of energy is a cause of deforestation. Furthermore, deforested areas are prone to soil erosion. 4. When dung or agricultural waste is used for fuel, it cannot be used as an additive to improve the fertility or organic content of the soil. Thus, the use of these materials for fuel negatively affects agricultural productivity.

Biomass- Effects on Food Production

- Although the use of marginal or underutilized land to grow energy crops may make sense, using fertile cropland does not. Since there are millions of people in the world who do not have enough food to eat, the conversion of land from food crops to energy crops presents ethical issues. - The use of crop residues and animal waste as a source of energy also presents some problems. These materials supply an important source of organic matter and soil nutrients for farmers. This is particularly true among subsistence farmers in the developing world. They cannot afford fertilizer and rely on these materials to maintain soil fertility. However, they also need energy. Thus, they must make difficult decisions about how to use this biomass resource.

Renewable energy

- provided by processes that replenish themselves or are continuously present as a feature of the solar system. - The sun is the primary source of renewable energy. In terms of world energy usage, biomass is the primary renewable energy source. The process of photosynthesis converts sunlight energy into plant biomass. - Since biomass is constantly being produced, it is a form of renewable energy. - Solar, wind, geothermal, and tidal energy are renewable energy sources because they are continuously available.

Anaerobic Digestion

- Anaerobic digestion involves the decomposition of wet and green biomass or animal waste through bacterial action in the absence of oxygen. This process produces a mixture, consisting primarily of methane and carbon dioxide, known as biogas. - The most commonly used technology involves small digesters on farms that generate gas for use in the home or for farm-related activities. - Anaerobic digestion also occurs in landfills. In many landfills the methane gas produced eventually escapes into the atmosphere. However, the gas can be extracted by inserting perforated pipes into the landfill. - In this way, the gas will travel through the pipes, under natural pressure, to be used as an energy source, rather than simply escaping into the atmosphere to contribute to greenhouse gas emissions. Some newer landfills have even been designed to encourage anaerobic digestion, which reduces the volume of the waste and provides a valuable energy by-product.

2. Hydroelectric Power

- At present, hydroelectricity provides about 16 percent of the world's electricity. In some areas of the world, hydroelectric power is the main source of electricity. - In South and Central America, 65 percent of the electricity comes from hydroelectric power. - Norway gets 95 percent of its electricity and nearly 60 percent of all its energy from hydroelectricity. - Canada gets 57 percent and the United States gets about 6 percent of its electricity from hydroelectric plants

a. Fuelwood

- Because of its bulk and low level of energy compared to equal amounts of coal or oil, wood is not practical to transport over a long distance, so most of it is used locally. - In less-developed countries, wood has been the major source of fuel for centuries. In fact, wood is still the primary source of energy for nearly half of the world's population. - In these regions, the primary use of wood is for cooking. In much of the less-developed world, cooking is done over open fires. - Using fuel-efficient stoves instead of open fires could reduce these energy requirements by 50 percent. - Improving efficiency would protect wood resources, reduce the time or money needed to obtain firewood, and improve the health of people because they would breathe less wood smoke

Unintended Consequences of the Renewable Fuel Mandate

- Between 2005, when the Energy Policy Act of 2005 was passed, and 2012, the amount of corn used for ethanol production increased to 40 percent of corn production. By 2016 corn used for ethanol production still accounted for over 30 percent of corn production. - This resulted in a temporary increase in the price of corn and the amount of land planted to corn. The amount of land increased 16 percent and the price increased 240 percent between 2005 and 2012. Between 2012 and 2016 the area planted and the price returned to normal. - Farmers took erodible farmland out of conservation programs and planted corn because they could make more money by planting corn than they could from agriculture programs that paid them to remove marginal lands from production. - Since the additional demand for corn to make ethanol caused the price to rise, farmers who needed to feed corn to livestock had to pay higher prices, resulting in increased costs of meat and dairy products. - Since farmers planted more corn and less of other crops, the prices of other crops rose because of a lower supply

1. Biomass Conversion

- Biomass fulfilled almost all of humankind's energy needs prior to the Industrial Revolution. All biomass is traceable back to green plants that convert sunlight into plant material through photosynthesis. Major Types of biomass: a. Fuelwood b. Waste c. Crop residues and animal wastes d. Energy Plantations

Biomass- Air pollution

- Burning wood is a source of air pollution. Often the people in developing countries use wood in open fires or poorly designed, inefficient stoves. This results in the release of high amounts of smoke (particulate matter) and other products of incomplete combustion, such as carbon monoxide and hydrocarbons, which contribute to ill health and death. - Respiratory illnesses are particularly common among women and children who spend the most time in the home. Even in the developed world, air pollution from the burning of biomass is a problem. - Because solid waste is likely to contain a mixture of materials, including treated paper and plastic, there are additional air pollutants released from the burning of waste.

The Renewable Fuel Mandate

- Congress passed two bills—the Energy Policy Act of 2005 and the Energy Independence and Security Act of 2007—that mandated specific amounts of renewable fuels in gasoline. Although these two laws addressed many energy-related issues, the following items relate to the renewable fuel mandate: 1. Subsidies were provided to build ethanol plants. 2. Different kinds of renewable fuels were identified—corn-based ethanol, cellulosic ethanol, biodiesel, and advanced fuels. Each fuel must demonstrate that it produces lower amounts of greenhouse gases than gasoline. 3. Gasoline producers were required to blend specific amounts of renewable fuels into gasoline or pay a fine. 4. A schedule of increasing amounts of each of the kinds of renewable fuels was required in gasoline from 2005 to 2020. 5. A tax credit of $0.45 per gallon of ethanol was provided to blenders who incorporated ethanol into their gasoline.

Biofuels production

- Ethanol can be produced by fermenting sugars. The sugars can be obtained directly from plants or may be produced by converting the starch or cellulose of plants to sugars. - Typically, sugar or starch is extracted from the biomass crop by crushing and mixing with water and yeast and then keeping the mixture warm in large tanks called fermenters. The yeast breaks down the sugar and converts it to ethanol and carbon dioxide. A distillation process is required to remove the water and other impurities from the dilute alcohol product. - In the United States, corn is used to produce ethanol, which is then blended with gasoline. Most gasoline in the United States contains about 10% ethanol because it is mandated by an act of Congress. The presence of ethanol does have beneficial effects. It improves engine efficiency, reduces air pollution, and reduces the likelihood that water will freeze in gas lines. - Biodiesel can be produced from the oils in a variety of crops, including soybeans, rapeseed, and palm oil as well as animal fats. These raw materials need to be modified chemically before they can be used as fuel. - Currently, about 2 percent of the diesel fuel consumed in the world is biodiesel. Europe leads the world in production of biodiesel fuel with about 50 percent of the total world production.

Passive solar systems

- In a passive solar system, light energy is transformed to heat energy when it is absorbed by a surface. Homes and buildings can be designed to use passive solar energy for heating and lighting, which reduces the need for nonrenewable energy sources. - Anyone who has walked barefoot on a sidewalk or blacktopped surface on a sunny day has experienced the effects of passive solar heating - Other passive solar heating designs involve sunspaces or trombe walls. - A sunspace (which is much like a greenhouse) is built on the south side of a building. As sunlight passes through glass, it warms the sunspace. Proper ventilation allows the heat to circulate into the building. - A trombe wall is a very thick, south-facing wall painted black and made of a material that absorbs a lot of heat. A pane of glass installed a few centimeters in front of the wall helps hold in the heat. The wall heats up slowly during the day; then, as it cools gradually during the night, it gives off its heat inside the building. - Daylighting is simply the use of natural sunlight to brighten a building's interior, reducing the need for electricity to light the interior of a building. To lighten north-facing rooms and upper levels, a clerestory—a row of windows near the peak of the roof on the sunny side of the buiding—is often used along with an open floor plan inside that allows the light to bounce throughout the building. - There are design features that can help keep passive solar buildings cool in the summer. For instance, overhangs can be designed to shade windows when the sun is high in the sky in the summer but allow sunlight to enter during the winter when the sun is lower in the sky. Sunspaces can be closed off from the rest of the building during the summer when heating is not needed. And a building can be designed to use fresh-air ventilation in the summer.

c. Crop residues and animal wastes

- In many parts of the world, the straw and stalks left on the field are collected and used to provide fuel for heat and cooking. Animal wastes are also used for energy. Animal dung is dried and burned or processed in anaerobic digesters to provide a burnable gas. - Crop residues are bulky and have a low energy-to-weight ratio. Thus, harvesting crop residues to burn or convert to ethanol makes sense only if the travel distance from field to processing plant is short. Removal of crop residues from fields has several negative agricultural impacts. - It leads to increased erosion, since the soil is more exposed, and reduces the benefits provided by organic matter in the soil, since the crop residues are not incorporated into the soil. - Finally, the production of ethanol from cellulose is currently not economical.

Energy Conservation: Government Incentives

- In recent years, the U.S. government has passed laws or established policies that will reduce average energy consumption. Most of these initiatives provide economic rewards in the form of tax incentives or impose economic penalties (taxes and fines). The following are examples of government actions designed to improve energy efficiency: 1. Imposition of improved fuel economy standards for new automobiles and trucks. 2. Tax incentives for those who upgrade insulation, windows, doors, heating and cooling systems, and other appliances. 3. Phaseout in 2014 of most uses of incandescent lightbulbs, which are very inefficient. The development of fluorescent and LED bulbs to replace them quickly followed. 4. Established higher energy efficiency standards for appliances. 5. Investment in more efficient electricity distribution. 6. Improvement in high-speed rail transportation

Biomass- Habitat and biodiversity loss

- It is estimated that throughout the world there are 1.3 billion people who cannot obtain enough wood or must harvest wood at a rate that exceeds its growth. This has resulted in the destruction of much forest land in Asia and Africa and has hastened the rate of desertification in these regions. - Another issue associated with biomass energy is the loss of biodiversity. Destroying natural ecosystems to plant sugarcane, grains, palm oil, or other plants can reduce the biodiversity of a region. The plantations lack the complexity of a natural ecosystem and are susceptible to widespread damage by pests or disease

d. Energy plantations

- Many crops can be grown for the express purpose of energy production. Crops that have been used for energy include forest plantations, sugarcane, corn, sugar beets, grains, kelp, palm oil, and many others. - Two main factors determine whether a crop is suitable for energy use. - Good energy crops have a very high yield of dry material per unit of land (dry metric tons per hectare). A high yield reduces land requirements and lowers the cost of producing energy from biomass. - Similarly, the amount of energy that can be produced from a biomass crop must be more than the amount of energy required to grow the crop

b. Photovoltaics

- Photovoltaics (PV) are solid-state semiconductor devices that convert light directly into electricity. Photovoltaics are usually made of silicon with traces of other elements. The basic structural unit is a photovoltaic cell (solar cell). Groups of solar cells can be combined into modules called solar panels and groups of panels can be connected to form arrays. - Three factors drive the photovoltaic industry: cost of the solar installation, efficiency of the system, and government policy. As the cost of the system is reduced and efficiency increases, the price per kilowatt-hour of electricity falls. Currently, the cost of installation is falling and efficiency is increasing. Electricity from photovoltaics is now less expensive in some places than electricity from the grid.

Pyrolysis

- Pyrolysis is a process for converting solid biomass to a more useful fuel. - Biomass is heated or partially burned in an oxygen-poor environment to produce a hydrocarbon-rich gas mixture, an oil-like liquid, and a carbon-rich solid residue (charcoal), which have a higher energy density than the original fuel. - In developing countries, charcoal kilns are simply mounds of wood or wood-filled pits in the ground that are set afire and then covered with earth. The smoldering fire slowly converts the wood to charcoal. - Gasification is a form of pyrolysis, carried out with more air and at high temperatures, to optimize the gas production. The resulting gas, known as producer gas, is a mixture of carbon monoxide, hydrogen, and methane, together with carbon dioxide and nitrogen. The gas is more versatile than the original solid biomass, and it can be used as a source of heat or used in internal combustion engines or gas turbines to produce electricity.

Energy Conservation

- The amount of energy used by a society is determined by many factors. These include the level of economic development, the cost of energy, societal expectations, and government policies related to energy use. - There is typically a relationship between the cost of an item and its energy efficiency. Often, poorly designed, energy-inefficient buildings and machines can be produced inexpensively. The short-term cost (purchase price) is low, but the long-term cost for upkeep and energy utilization is high. Typically, the cost of more efficient buildings or machines is higher, but the difference in initial price is made up by savings in energy cost over several years. This is known as the payback period. - For ex: Fluorescent lightbulbs

Technology for Obtaining Hydropower

- The most common type of hydroelectric power plant uses a dam on a river to store water in a reservoir. (See figure 10.8.) Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity Largest Hydroelectric plants: Table 10.1 Three Gorges Dam, China Itaipu, Brazil/Paraguay Xiluodu, China Guri, Venezuela

3. Solar Energy

- The sun is often mentioned as the ultimate answer to the world's energy problems. It provides a continuous supply of energy that far exceeds the world's demands. In fact, the amount of energy received from the sun each day is 600 times greater than the amount of energy produced each day by all other energy sources combined - BUT, provides less than 1% of energy needs - Solar energy is utilized in three ways: 1. In a passive heating system, the sun's energy is converted directly into heat for use at the site where it is collected. 2. In an active heating system, the sun's energy is converted into heat, but the heat must be transferred from the collection area to the place of use. 3. The sun's energy also can be used to generate electricity by heating water to turn turbines or by using photovoltaic cells.

Technology for Obtaining Tidal Energy

- The technology required to convert tidal energy into electricity is very similar to that used in traditional hydroelectric power plants. The first requirement is a dam or "barrage" across a tidal bay or estuary. Building such dams is expensive. Therefore, the best tidal sites are those where a bay has a narrow opening, thus reducing the length of dam required. At certain points along the dam, gates and turbines are installed. When the difference in the elevation of the water on the two sides of the barrage is adequate, the gates are opened. As the water flows from the high side to the low side of the dam, the flowing water causes turbines to spin and produce electricity. - Although the technology required to harness tidal energy is well established, tidal power is expensive, and only two major tidal generating stations are in operation; the 254-megawatt Sihwa Lake Tidal Power Station in South Korea and the 240-megawatt La Rance River Tidal Power Plant on the northern coast of France.

Tidal Power- Environmental Issues

- Tidal energy is a renewable source of electricity and does not contribute to climate change. However, changing tidal flows by damming a bay or estuary could result in negative impacts on aquatic and shoreline ecosystems, as well as affecting navigation and recreation. - Studies have shown that environmental impacts depend on the site and local geography - Local tides changed only slightly due to the La Rance barrage, and the environmental impact has been negligible, but this may not be the case for all other sites.

6. Tidal Power

- Tides are caused by the gravitational force exerted by the moon and the sun. - The magnitude of the gravitational attraction between two objects depends on the masses of the objects and the distance between them. The moon exerts a larger gravitational force on the Earth because, although it is much smaller in mass than the sun, it is a great deal closer than the sun. This force of attraction causes the oceans, which make up 71 percent of the Earth's surface, to bulge along an axis pointing toward the moon. (There is also a bulge on the side of the Earth farthest from the moon because the moon is pulling the Earth away from the water on its surface.) - Tides are produced by the rotation of the Earth beneath this bulge in its watery coating, resulting in the rhythmic rise and fall of water levels that can be observed along coasts. - Thus, there are two high and two low tides each day. When the sun, moon, and Earth are in a line, the combined effects of sun and moon generate higher tides. - To produce practical amounts of power, a difference between high and low tides of at least 5 meters (16 feet) is required. About 40 sites around the world have this tidal range. - The higher the tides, the more electricity can be generated from a given site and the lower the cost of electricity produced.

Compare a passive solar heating system with an active solar heating system.

A passive solar system is a design that allows for the entrapment and transfer of heat from the sun to a building without the use of moving parts or machinery. An active system is one that traps sunlight energy as heat energy and uses mechanical means to move it to another location.

Photosynthesis

Carbon dioxide + water + Sunlight energy -> Biomass (chemical energy) + oxygen - This energy is stored in the organic molecules of the plant as wood, starch, oils, or other compounds. Any form of biomass—plant, animal, alga, or fungus—can be traced back to the energy of the sun. Since biomass is constantly being produced, it is a form of renewable energy.

What are the general characteristics of renewable energy sources?

Renewable energy sources can replenish themselves continuously

Solar-Generated Electricity

Solar energy can be used to generate electricity in two different ways. It can be used to create steam that is used to run a turbine similar to that of a conventional power plant, or photovoltaic cells can be used to generate electricity directly from sunlight. a. Conventional electric generation b. Photovoltaics

List three energy conservation techniques.

• Switch to highly efficient fluorescent light bulbs • Buy energy efficient appliances • Install low emmissive glass windows.