1 Chapter 5 Renewable Energy Sources II Alternative Sources of Energy
2 Introduction & Motivation Solar Energy is an unlimited source of energy great alternative to fossil fuels easily accessible to anyone limited by the cost and the need for research into making this resource more efficient and environmentally friendly. Alternative Sources of Renewable Energy Water hydroelectric energy use change in height of a column of water to produce electricity. Wind energy from the spinning planet use the earth s rotation to turn a wind turbine and produce electricity Geothermal energy from the earth use the fact that there exist temperature gradients in materials to extract useful energy to produce electricity. Biomass plant material, vegetation, or agricultural waste that can be used as a fuel source.
3 Introduction & Motivation Natural flow of energy to and from the earth. Energy flow from the sun is shown on the left while energy flow from the earth on the right. Where does the energy flow of the earth originate from? Where does nuclear energy and thermal gradients in the earth s crust come from?
4 Introduction & Motivation Worldwide renewable energy by type in gigawatts. Most of the worlds alternative energy is in hydroelectric power. The second/third most are biomass heating and solar energy. Let s start by looking at water and wind
5 Hydropower Water & The Waterwheel Water hydroelectric energy use change in height of a column of water to produce electricity. Using the flow of water has been a source of energy for millennia. Waterwheels have been used to ease human labor. Waterwheels turn a shaft that converts the force of the water into mechanical energy. Ancient Chinese waterwheel for smelting ore to make weapons and agricultural tools. This is from around ~31AD.
6 Hydropower Waterwheels through the ages Medieval Europe Tidal mills were constructed in low lying areas near the ocean. Dams containing swinging gates were built along shallow creeks. As the tide came in, the gates swung open inwardly. Water filled the area behind the dam. When the tide turned, the gates swung shut, forcing the water to flow seaward through the mill race of the tidal mill. Tidal_mill_Brehat_France.jpg/300px- Tidal_mill_Brehat_France.jpg Historic America Water to turn the wheel is provided from a spring located near the sawmill. The shaft of the wheel is connected to a gear and belt that moves a saw back and forth to cut lumber.
7 Hydropower The Modern Waterwheel A modern water wheel and tidal mill used to generate electricity. A channel is made and a waterwheel is placed in the channel. As the tide ebbs and flows the rushing water turns a propeller (which is a variant of a waterwheel) and this is used to turn a turbine and make electricity.
8 Hydroelectric Power Energy from Falling Water Some Facts: Hydropower provides about 96 percent of the renewable energy in the United States. Other renewable resources include geothermal, wave power, tidal power, wind power, and solar power. Hydroelectric power plants do not use up resources to create electricity nor do they pollute the air, land, or water, as other power plants may. Hydroelectric power has played an important part in the development of this Nation's electric power industry. Both small and large hydroelectric power developments were instrumental in the early expansion of the electric power industry. Source: US Dept. of the Interior
9 Hydroelectric Power Worldwide Usage Reminder of the worldwide use of energy by type. Alternative sources account for less than 20% of the worlds energy use. Fossil fuels account for over 80% of the worlds energy use. Worldwide use of hydroelectric power in yellow. The feasibility by continent of using hydroelectric energy to a greater extent.
10 Hydropower The Hydrologic Cycle As the water is channeled through the dam there is a change (a loss in fact) in the potential energy of the water. The loss of potential energy is turned in to kinetic energy in a turbine in the dam facility. The turbine turns a coil of wire in a generator, and by Faraday s law, produces a current. The loss of potential energy is transformed in to electric energy.
11 Hydropower How a Hydroelectric Dam Operates Water from a dammed up river or lake flows through the control gate and through a Penstock into the turbine. At night or when demand is low, water can be pumped back up to the reservoir. This takes energy, but we can cycle the system to be ready for later demand. The inflow of water spins the turbine and this in turn spins the connected shaft. The spinning shaft is connected to a rotor that generates electricity by Faraday s law. water_turbine.jpg
12 Hydropower Transmission of Electricity The electricity generated is distributed from large systems to smaller systems. The electricity (the potential in particular) is stepped up to a high voltage (and low current) by the transformer and then is sent down the high voltage lines. The high voltage lines are connected to substations which step down the voltage to usable levels and higher current. The current then flows down localized power lines to your house.
13 Hydropower Pros & Cons Hydroelectric Dam - Pros Dams can store rain water or water directly from the river itself. Then, in case of a drought, the dam will still have a relatively constant supply of water. These produce clean environmentally friendly electricity. Controls flooding & provides recreational activities such as boating fishing and swimming, if the lake is not being used for drinking water. Simple design makes for inexpensive repairs and maintenance costs and hence very few breakdowns. Produce inexpensive (after completion) and clean power. Renewable energy source, because the water is not destroyed by passing through the dam. If needed, dams can be shut down instantly, where thermal plants take hours, and nuclear plants can take days. Hydroelectric Dam - Cons Hydroelectric power production requires flooding of entire valleys and scenic areas. Disrupts natural seasonal changes in the river and ecosystems can be destroyed. Ends flooding that help to clean out the silt in rivers, causing them to clog. The silt that usually flows down to the beaches and estuaries are blocked by the dam. Studies show that the plant decay caused downstream of major dams produces as many greenhouse gasses as more conventional methods of producing electricity. Dams are expensive to build, and due to drought may become useless, or produce much less power than originally planned. Dams can break and cause massive flash flood.
14 Hydropower An example Suppose that 750,000 gallons of water per second (~2835 m 3 /s) flow over Niagara Falls and that this water is used to generate electricity. If the water has a speed of 40 mph and that the water falls an average of 30m, what is the total electric power generated if all of the energy of the water going over the falls used? Hint: What type of energy does the water have at the top of the falls and what is it converted into at the turbine?
15 Hydropower An example The solution Power is the rate at which energy is transferred. Power = Energy time In the problem we are given the volume per unit time. Taking the equation for power let s multiply and divide by a volume of water. Thus we have Power = Energy time volume volume = Energy volume volume time But what is the energy per volume of fluid? Using the hint we have at the top of the falls, the water has a KE and a PE and at the bottom of the falls we turn the loss of PE into a gain in KE. Thus we have Energy volume = KE bottom volume = KE + mgh top = volume Energy volume = 1 ( kg 1000 ) 17.9 m m 2 3 s ( ) kg 1 mv 2 2 tiop + mgh volume ( )( 9.8 m ) 30m s 2 m 3 = 1 2 ρv 2 top + ρgh ( ) = J m 3 And the power is Power = J 2835 m 3 m 3 s = W =1.29GW
16 Hydropower The Hydroelectric Dam The solid line shows the energy usage (scale on the left) in the United States. The dashed curve (scale on right) shows the percentage of the US electricity provided by hydroelectric sources. In general what trends do you see?
17 Hydropower US Undeveloped Regions around the US with with large undeveloped hydroelectric power resources. What factors would limit the development of hydroelectric power in these areas?
18 Wind Spinning Planet, Weather and a Breeze Wind is caused by the uneven heating of the earth by the sun. During the day, the earth's land masses heat up, and the air above them rises. The earth's water heats up more slowly, and the cooler air above the water is drawn across the land by the rising land air, creating wind. At night, the winds change because the land cools down more quickly than the water. Wind energy is harnessed using aerodynamic blades that spin due to the flow of the wind over their surfaces.
19 Wind Turbine Types: Horizontal Design All moving objects, including invisible air particles, have kinetic energy. In order to collect this energy, we can use wind turbines, which are essentially backwards fans; fans turn electricity into wind, turbines turn wind into electricity. As the air flows over the fan blade there is a difference in pressure generated over the blade. media/horizontal_axis_wind_turbines.jpg This difference in pressure creates a force and causes the blade to spin. This difference in pressure is due to the difference in wind speeds across the blade and this is an application of Bernoulli s principle. Bernoulli s principle: Pressure inversely proportional to velocity.
20 Wind Turbine Types: Horizontal Design As the fan blade spins, the main shaft turns. This main shaft is connected to a gear box which in turn spins another shaft at a much higher rate. The high speed shaft is connected to a generator and the generator produces electricity. The electricity is channeled through wires to the bottom of the tower.
21 Wind Turbines Energy Production The energy available in wind is proportional to the area it is passing through, and the cube of its velocity. For a given wind speed, if you double the radius of the turbine (quadruple the area), you quadruple the power generated. For a given turbine size, if you double the wind speed, you increase the power generated by a factor of eight. A wind turbine collects energy from the wind with asymmetrical blade surfaces, which cause different air velocities on the two sides, creating a pressure differential, and the aerodynamic lift force that spins the turbine. Air drag on the blade surfaces slows the spinning of the blades. Usually you want high lift and low drag, but this depends on the wind speeds you're working with. You can control the ratio between the two to optimize generator efficiency. P W = 1 2 ρπr2 v 3
22 Wind Turbines Energy Production The energy produced depends on the physical area swept out by the fan blades. Here is a graphic showing the development of large scale wind turbines with increasing rotor blade size. As blade size increases the power output increases Rotor (meters) Rating (KW) ,650 Annual MWh ,480 2,200 5,600 How big can you make these?
23 Wind Turbine Types: Vertical Design In a vertical design, the shaft is mounted on a vertical axis, perpendicular to the ground. Vertical design turbines are always aligned with the wind, unlike their horizontal axis counterparts. Unlike a horizontal axis turbine, whose orientation needs to be adjusted when the wind direction changes, there's no adjustment necessary when the wind direction changes using the vertical design.
24 Wind Turbine Types: Vertical Design However, a drawback with a vertical turbine is that a vertical turbine cannot get started on its own, it needs a boost from its electrical system to get started. Instead of a tower, it typically uses guy wires for support, so the rotor elevation is lower. Lower elevation means slower wind due to ground interference, so vertical design turbines are generally less efficient than horizontal wind turbines. On the upside, all equipment is at ground level for easy installation and servicing; but that means a larger footprint for the turbine, which is a big negative in farming areas.
25 Wind Turbine Types A Novel Idea Take two horizontal axis wind turbines and mount them on highway sign tubes. The turbines spin due to turbulence created from passing cars. The turbines are connected to generators, just like a traditional wind turbine, and the energy generated could be used to power say a small apartment for a year. That s not a lot, but it s a start.
26 Wind Energy Distribution by State in the US Distribution of wind farms by states in the US. Total power output is 12.6 GW per year. Why do you think there are little to no wind farms in Nv, Ut and Az? What about the south east US?
27 Wind Energy Worldwide Distribution Worldwide growth of wind energy has increased exponentially over the past 10 years. Worldwide usage of wind energy by country.
28 Wind Energy Off Shore Wind Farms The Future? Imagine putting wind farms off of the coasts of countries with high winds. Could we power the needs of the entire world with all countries participating? Would this work?
29 Wind Energy Pros & Cons Eco-friendliness The amount of land used for the construction of a wind turbine is an issue of debate. The advocates of wind energy state that the amount of land needed for building a windmill is only equal to the dimensions of its base. All the remaining space can be used for farming. According to them, the farmers can earn lots of money by renting out a portion of their land to companies that harness wind power. They can even build their own windmills and lease them out. The opponents, on the other hand, believe that space occupied by the wind turbine is many times more than the dimensions of the base. Apart from the area occupied by the base, safety zone is needed, which should be least 5 acres. Besides this, all the trees within 30 acres should also be cleared. Transmission lines have to be laid and roads have to be built for the upkeep of the turbine. For one megawatt of power output approximately 50 acres of land would be needed. Another issue of distress is the birds that are killed by the movement of the blades. Advocates of windmills state that hundreds of birds are also killed by pollution, planes, and other stationary structures. The opponents insist that the percentage of birds killed by windmills is far greater than those killed by pollution or planes. Noise is another disconcerting aspect of wind turbines. The blade movement produces a lot of noise.
30 Wind Energy Pros & Cons Reliability The modern electrical grids are designed to operate efficiently 99.9% of the time; the remaining 0.1% of inefficiency can be easily handled. With wind turbines, they are operational only when the wind blows. Furthermore, if the wind doesn t blow at constant rate, it becomes difficult to manage the power production. Unlike electrical grids, wind power is not dispatchable it cannot be started immediately if the wind is not blowing. Cost Wind turbines do not require expensive boilers, reactors, engines and fuel, so they are relatively cheap. However, the money saved is spent on purchasing high-priced gearboxes, towers, propellers, electronic control systems and forth. Moreover, windmills have a capacity factor of 30 percent if a wind turbine has one-megawatt power generation capacity, it will produce only 300-kilowatts of power. To maintain reliability, grid energy storage would be required to store energy produced on a windier day. Thus, the running cost of a wind turbine is somewhat high.
31 Current Event News: Cape Cod Wind Farms Homework for Hydroelectric and Wind Energy Chapter 5: Questions: 5.1, & 5.4, MC: 5.1, 5.4, 5.6, & 5.7
32 Geothermal - Ocean Thermal Energy Conversion (OTEC) The oceans cover a little more than 70 percent of the Earth's surface. This makes them the world's largest solar energy collector and energy storage system. On an average day, 60 million square kilometers (23 million square miles) of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil. If less than one tenth of one percent of this stored solar energy could be converted into electric power, it would supply more than 20 times the total amount of electricity consumed in the United States on any given day. OTEC, or ocean thermal energy conversion, is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean's natural thermal gradient
33 Geothermal - Ocean Thermal Energy Conversion (OTEC) Distribution of temperature gradients in the oceans across the globe.
34 Geothermal A Closed OTEC System Surface water heats a fluid with a low boiling point, such as ammonia, and this evaporates the fluid. The ammonia is a vapor under pressure. The expanding (and cooling) ammonia gas is used to drive the turbine which is connected to a generator. The gas is further cooled by passing it through cold water pumped up from the bottom of the ocean via massive fiberglass tubes pull up cold water. Water pumps bring cold deep water through pipes to a condenser on the surface. The cold water condenses the steam, and the closed cycle begins again. ocean_thermal_energy_conversion.jpg
35 Geothermal A Closed OTEC System by Lockheed-Martin
36 Geothermal Energy Wave Energy Wave energy conversion takes advantage of the ocean waves caused primarily by interaction of winds with the ocean surface. Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid. Although many wave energy devices have been invented, only a small proportion have been tested and evaluated. Furthermore, only a few have been tested at sea, in ocean waves, rather than in artificial wave tanks. A wave energy converter may be placed in the ocean in various possible situations and locations. It may be floating or submerged completely in the sea offshore or it may be located on the shore or on the sea bed in relatively shallow water. A converter on the sea bed may be completely submerged, it may extend above the sea surface, or it may be a converter system placed on an offshore platform. Apart from wave-powered navigation buoys, however, most of the prototypes have been placed at or near the shore.
37 Geothermal Energy Wave Energy According to the European Union, "Among the different converters capable of exploiting wave power, the most advanced is unquestionably the Pelamis Wave Energy Converter, a kind of "undulating sea serpent" developed by Ocean Power Delivery. This technology is the object of a commercial contract for installation of a farm in Portugal. In 2007, three machines, with a total capacity of 2.25 megawatts, are in installation phase, and should be joined by 27 others in the years to come. Another 5 MW project is being studied for England this time." None of these plants are located in California, although economic feasibility studies have been performed for a 30 MW wave converter to be located at Half Moon Bay. Additional smaller projects have been discussed at Fort Bragg, San Francisco and Avila Beach. There are currently no firm plans to deploy any of these projects As of the mid-1990s, wave energy conversion was not commercially available in the United States. The technology was in the early stages of development and was not expected to be available within the near future due to limited research and lack of federal funding. Research and development efforts are being sponsored by government agencies in Europe and Scandinavia.
38 Geothermal Energy Wave Energy Many research and development goals remain to be accomplished, including cost reduction, efficiency and reliability improvements, identification of suitable sites in California, interconnection with the utility grid, better understanding of the impacts of the technology on marine life and the shoreline. Also essential is a demonstration of the ability of the equipment to survive the salinity and pressure environments of the ocean as well as weather effects over the life of the facility Issues: Disturbance or destruction of marine life (including changes in the distribution and types of marine life near the shore) Possible threat to navigation from collisions due to the low profile of the wave energy devices above the water, making them undetectable either by direct sighting or by radar. Also possible is the interference of mooring and anchorage lines with commercial and sport-fishing. Degradation of scenic ocean front views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines.
39 Geothermal Energy Wave Energy The Pelamis Pelamis: The first commercial wave energy generator installed in Agucadoura, Portugal gif/_ _wave_power_pelamis_inf416.gif Power spectrum (versus wave frequency) for the Pelamis in action.
40 Geothermal Energy Energy from beneath the Earth
41 Geothermal Energy Energy from beneath the Earth
42 Geothermal Energy Energy from beneath the Earth
43 Geothermal Energy Energy from beneath the Earth