Chapter 9 - Alternative Energy Use PDF

Chapter 9 Alternative Use of Energy Chapter 9 Alternative Use of Energy 9.1 Solar Thermal Systems 9.2 Photo Voltaic Systems 9.3 Wind Power Alternative Use of Energy An alternative energy source is a non-depleting or renewable energy source....

Chapter 9 Alternative Use of Energy Chapter 9 Alternative Use of Energy 9.1 Solar Thermal Systems 9.2 Photo Voltaic Systems 9.3 Wind Power Alternative Use of Energy An alternative energy source is a non-depleting or renewable energy source. Alternative energy sources, for example solar and wind, were, back in time, important conventional sources of energy. Conversely, natural gas, coal, and oil were, at some time in history, alternative energy sources. Government funding for R&D as well as tax incentives in the alternative energy area dropped sharply during the decade of the eighties and early nineties.  9.1 Solar Thermal Systems Introduction Solar Irradiance Solar Thermal Collectors Thermal Storage Systems Introduction (Solar Energy) 𝑻𝒔𝒖𝒓𝒇𝒂𝒄𝒆 = 𝟓𝟕𝟕𝟖 𝑲 𝟓𝟓𝟎𝟓℃ 𝑻𝒄𝒐𝒓𝒆 = 𝟏𝟓. 𝟔 × 𝟏𝟎𝟔 𝑲 𝐏𝐨𝐰𝐞𝐫 = 𝟑. 𝟖𝟓 × 𝟏𝟎𝟐𝟔 𝑾𝒂𝒕𝒕𝒔 𝑲𝑾.𝒉𝒓 𝐄𝐧𝐞𝐫𝐠𝐲 = 𝟑. 𝟑𝟕 × 𝟏𝟎𝟐𝟕 𝒚𝒓 Annual Energy Intercepted (on Earth): 𝟏. 𝟓 × 𝟏𝟎𝟏𝟖 KW.hr/year (0.000000045%) World Energy Demand: 𝟏. 𝟒 × 𝟏𝟎𝟏𝟒 KW.hr /year (0.0093%) - Total: 𝟒. 𝟐 × 𝟏𝟎−𝟏𝟐 % Solar Irradiance (Distribution) The MENA region receives the highest solar irradiance all over the globe.  Solar Irradiance (Orientation) To collect the maximum possible amount of energy, the designer should estimate the solar radiation angle to remain perpendicular to it Solar Irradiance (Splitting) Solar Irradiance (Numerical Facts) Solar energy arrives at the earth’s atmosphere at a rate of about 1353 W/m2 (428 Btu/hr ft2). This value is referred to as the solar constant. Part of this radiation is reflected back to space, part is absorbed by the atmosphere and re- emitted, and part is scattered by atmospheric particles. As a result, only about two-thirds of the sun’s energy reaches the surface of the earth. For example: at 40° north latitude, the noontime radiation rate on a flat surface normal to the sun’s rays is about 946 W/m2 (300 Btu/hr ft2 ) on a clear day. A solar collector tracks the sun to be always normal to the sun’s rays. Since no collector is perfect and might collect only 70% of the energy striking it, and since the percent sunshine might also be about 70%, a more realistic area would be about 53 m2 (567 ft2) to provide 293 kWh (1e6 Btu) of energy per day. Solar Thermal Collectors Non-concentrating collectors 1. Flat plate 2. Evacuated tube 3. Volumetric air Concentrating collectors 4. Parabolic Trough 5. CSP 6. Fresnel 7. Solar Power Tower 8. Solar Dish Sterling Engine 1. Flat plate collectors 1. Flat plate collectors Tracking-type collectors are usually used where relatively high temperatures (above 120°C) are required. The flat-plate collector is usually oriented South (if in the northern half of the globe). Its purpose is to harvest the solar radiation that falls upon it to raise the temperature of a fluid (coolant: can be air or water) 1 above the ambient conditions. 2 The heated fluid is used to provide hot water or space 6 7 heat, to drive an engine or a refrigerating device, or 1. Glazing 3 perhaps to remove moisture from a substance. 2. Absorber plate 3. Flow tubes 4 4. Insulation 5. Casing 5 6. Fluid in (cold) 7. Fluid out (hot) 2. Evacuated tubes (vacuum tubes) Its concept is very similar to a flat plate the glass tube permits the solar radiation Heat is trapped from escaping through convection due to the vacuum 3. Volumetric air collector Air collectors have distinct advantages over liquid collectors: Freezing is not a concern. Leaks, although undesirable, are not as detrimental as in liquid systems. Corrosion is less likely to occur 4. Parabolic Trough Temperature range 250-450oC Concentrating collectors provide relatively high temperatures for applications such as power generation. They generally cannot use the diffuse or scattered radiation from the sky and must track the sun’s direct radiation. 5. Compound Parabolic Concentrator (CPC)  Used in residential and commercial heating applications 6. Fresnel  It is composed of multiple smaller flat mirrors that concentrate the radiation similar to parabolic troughs, however, simpler and cheaper. 7. Solar Power Tower A set of two-axis tracking mirrors (heliostats) track the sun reflecting light to the tower top. It uses molten salt (Sodium Nitrate NaNO3 ) as a coolant for its huge thermal capacity. 8. Solar Dish Concentrator It uses a generator at the receiver to directly generate AC power. Thermal Storage Systems Because energy demand is almost never tied to solar energy availability, a storage system is usually a part of the solar heating or cooling system. 1. With air-type collectors, however, a rock-bed type of storage is sometimes used. 2. The most common solar thermal storage system is one that uses water, usually in tanks. Water also freezes, and therefore in most climates, the system must either (1) drain all of the collector fluid back into the storage tank, or (2) use antifreeze in the collectors and separate the collector fluid from the storage fluid by use of a heat exchanger.  Solar Cells (photovoltaics) How solar cells work? What types of solar cells? How to determine the size of a PV system? Solar Cells (photovoltaics) How solar cells work? Solar cells use the electronic properties of semiconductor material to convert sunlight directly into electricity. Most solar cells are composed of very large area of p-n junction diodes.  Solar Cells (photovoltaics) A p-n junction has electronic asymmetry. The n-type regions have large electron densities but small hole densities. Electrons flow readily through the material but holes find it very difficult. p-type material has the opposite characteristic. Excess electron-hole pairs are generated throughout the p-type material when it is illuminated. Electrons flow from the p-type region to the n-type and a flow of holes occurs in the opposite direction. Example PV Power output: 𝐽𝑡𝑜𝑡 𝑃𝑚𝑝 = 𝑃𝑆𝑇𝐶 1 − 𝛽 𝑇 − 25 × 𝑛 1000 Example: Calculate the power output from a PV panel at 60 oC with 840 W/m2 incident solar radiation if the same panel produces 150 W at STC (1000 W/m 2 & 25oC). 𝛽 is measured at 0.003 W/K. 840 𝑃 = 150 1 − 0.003 60 − 25 × 1 = 112.8 𝑊 1000 For the Same situation, calculate the power output if the temperature was 30oC, 𝛽 is again measured at 0.003 W/K 840 𝑃 = 150 1 − 0.003 30 − 25 × 1 = 124.1 𝑊 1000  Wind Energy Introduction Wind Calculations Wind Turbine Types  Introduction Wind is a form of solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth. This wind flow, or motion energy, when "harvested" by modern wind turbines, can be used to generate electricity  Introduction 1 𝑃𝑇 = 𝐶𝑝 𝐴𝜌𝑣 3 2 Wind speed: The amount of energy in the wind varies with: Density of the air: Air density varies with elevation and temperature. Air is less dense at higher elevations than at sea level, and warm air is less dense than cold air. Swept area of the turbine: The larger the swept area (the size of the area through which the rotor spins), the more power the turbine can capture from the wind. Since swept area is A = 𝜋𝑟 2 (r = rotor blade length), a small increase in blade length results in a larger increase in the power available to the turbine. The cube of the wind speed. WIND Calculations  Wind Turbine Types Modern wind turbines fall into two basic groups: 1. The horizontal-axis variety, like the traditional farm windmills used for pumping water, 2. The vertical-axis design, like the eggbeater-style Darrieus model, named after its French inventor. Most large modern wind turbines are horizontal-axis turbines.  Wind Turbine Types Horizontal-axis turbines Advantages Horizontal-axis turbines are similar Blades are to the side of the turbines center of gravity, helping to propeller airplane engines. stability Horizontal-axis turbines have blades Ability to pitch the rotor blades in a storm to minimize damage like airplane propellers, and they Tall tower allows access to stronger wind in sites with wind shear commonly have three blades. The largest horizontal-axis turbines are as Most are self-starting tall as 20-story buildings and have Disadvantages blades more than 100 feet long. Taller Difficulty operating in near ground winds turbines with longer blades generate Difficult to transport (20% of equipment costs more electricity. Nearly all of the wind turbines currently in use are Difficult to install (require tall cranes and skilled operators horizontal-axis turbines. Difficult maintenance  Wind Turbine Types Vertical-axis turbines Vertical-axis turbines look like egg beaters, Advantages Vertical-axis turbines have blades that are Easy to maintain attached to the top and the bottom of a vertical Lower construction and transportation costs rotor. The most common type of vertical-axis Not directional turbine—the Darrieus wind turbine, named after Disadvantages the French engineer Georges Darrieus who Less efficient patented the design in 1931—looks like a giant, two-bladed egg beater. Some versions of the Operate in lower, more turbulent wind vertical-axis turbine are 100 feet tall and 50 feet Low starting torque and may require energy to start turning wide. Very few vertical-axis wind turbines are in use today because they do not perform as well as horizontal-axis turbines. Wind Turbine Types Turbine Components Horizontal turbine components include: blade or rotor, which converts the energy in the wind to rotational shaft energy; a drive train, usually including a gearbox and a generator; a tower that supports the rotor and drive train; and other equipment, including controls, electrical cables, ground support equipment, and interconnection equipment.