The three basic components of a geothermal plant are (1)a production well to bring the resource to the surface, (2)a turbine generator system for energy conversion, and(3)an injection well to recycle the spent geothermal fluids back into the reservoir Worldwide deployment of geothermal plants reached 5000 Mw by 1987 in 17 countries. Nearly one-half of this was in the United States. The Geysers plant north of San Francisco is the largest in the world with an installed capacity of 516 MW. In some developing countries, the Philippines for example, geothermal plants supply nearly 20% of their electrical needs The origin of tidal energy is the upward-acting gravitational force of the moon, which results in a cyclic variation in the potential energy of water at a point on the earths surface. These variations are amplified by topographical features such as the shape and size of estuaries. The ratio between maximum spring tide and minimum at neap can be as much as 3 to 1. In estuaries, the tidal range can be as large as 10 to 15 m. Power can be generated from a tidal estuary in two basic ways. a single basin can be used with a barrage at a strategic point along the estuary. By installing turbines at this point, electricity can be generated both when the tide is ebbing or flooding. In the two-basin scheme, generation can be time-shifted to coincide with hours of peak demand by using the basins alternately As can be expected, tidal energy conversion is very site-specific. The largest tidal power plant is the single basin scheme at La Rance in Brittany, France. It is rated at 240 MW and employs 24 vane-type horizontal turbines and alternator motors, each rated at 10 MVA. The plant has been in operation since 1966 with good technical and economic results. It has generated, on the average, around 500 GWh of net energy per year. The Severn estuary in the southwest of England and the Bay of Fundy in the border between the United States and Canada with the highest known tidal range of 17 m have been extensively studied for tidal power generation. There are several other possible sites around the world, but the massive capital costs required have delayed their exploitation Fuel cells A fuel cell is a simple static device that converts the chemical energy in a fuel directly, isothermally, and continuously into electrical energy Fuel and oxidant(typically oxygen in air)are fed to the device in which an electrochemical reaction takes place that oxidizes the fuel, reduces the oxidant, and releases energy. The ener released is in both electrical and thermal forms. The electrical part provides the required output. Since a fuel cell completely bypasses the thermal-to-mechanical conversion involved in a conventional power plant and ince its operation is isothermal, fuel cells are not Carnot-limited. Efficiencies in the range of 43 to 55% are forecasted for modular dispersed generators featuring fuel cells The low(< 0.05 lb/MWh) airborne emissions of fuel cell plants make them prime candidates for siting in urban areas. The possibility of using fuel cells in combined heat and power( CHP)units provides the cleanest and most efficient energy system option utilizing valuable (or imported) natural gas resources. Hydrocarbon fuel(natural gas or LNG)or gasified coal is reformed first to produce hydrogen-rich(and sulphur-free) gas that enters the fuel cell stack where it is electrochemically "burned"to produce electrical and thermal outputs. The electrical output of a fuel cell is low-voltage high-current dc. By utilizing a properly ty Early MW-scale demonstration plants employed phosphoric acid fuel cells. Molten carbonate fuel cell systems have shown considerable promise in recent years with demonstrated efficiencies in the 50 to 55% range based on the higher heating value. Another competitor in the long range is the solid oxide fuel cell that can be intergrated with a coal gasifier and a steam bottoming cycle Solar -Thermal-Electric Conversion The quality of thermal energy needed for DG employing solar-thermal-electric conversion necessitates concen- trated sunlight. Parabolic troughs, parabolic dishes, and central receivers are used to generate temperatures in the range of 400 to 500, 800 to 900, and >500 C, respectively. Technical feasibility of the central receiver system was demonstrated in the early 80s by the 10-MWe Solar One system in Barstow, California. Over a six-year period, this system delivered 37 GWh of net energy to the e 2000 by CRC Press LLC© 2000 by CRC Press LLC The three basic components of a geothermal plant are (1) a production well to bring the resource to the surface, (2) a turbine generator system for energy conversion, and (3) an injection well to recycle the spent geothermal fluids back into the reservoir. Worldwide deployment of geothermal plants reached 5000 MW by 1987 in 17 countries. Nearly one-half of this was in the United States. The Geysers plant north of San Francisco is the largest in the world with an installed capacity of 516 MW. In some developing countries, the Philippines for example, geothermal plants supply nearly 20% of their electrical needs. Tidal Energy The origin of tidal energy is the upward-acting gravitational force of the moon, which results in a cyclic variation in the potential energy of water at a point on the earth’s surface. These variations are amplified by topographical features such as the shape and size of estuaries. The ratio between maximum spring tide and minimum at neap can be as much as 3 to 1. In estuaries, the tidal range can be as large as 10 to 15 m. Power can be generated from a tidal estuary in two basic ways. A single basin can be used with a barrage at a strategic point along the estuary. By installing turbines at this point, electricity can be generated both when the tide is ebbing or flooding. In the two-basin scheme, generation can be time-shifted to coincide with hours of peak demand by using the basins alternately. As can be expected, tidal energy conversion is very site-specific. The largest tidal power plant is the single￾basin scheme at La Rance in Brittany, France. It is rated at 240 MW and employs 24 vane-type horizontal turbines and alternator motors, each rated at 10 MVA. The plant has been in operation since 1966 with good technical and economic results. It has generated, on the average, around 500 GWh of net energy per year. The Severn estuary in the southwest of England and the Bay of Fundy in the border between the United States and Canada with the highest known tidal range of 17 m have been extensively studied for tidal power generation. There are several other possible sites around the world, but the massive capital costs required have delayed their exploitation. Fuel Cells A fuel cell is a simple static device that converts the chemical energy in a fuel directly, isothermally, and continuously into electrical energy. Fuel and oxidant (typically oxygen in air) are fed to the device in which an electrochemical reaction takes place that oxidizes the fuel, reduces the oxidant, and releases energy. The energy released is in both electrical and thermal forms. The electrical part provides the required output. Since a fuel cell completely bypasses the thermal-to-mechanical conversion involved in a conventional power plant and since its operation is isothermal, fuel cells are not Carnot-limited. Efficiencies in the range of 43 to 55% are forecasted for modular dispersed generators featuring fuel cells. The low (< 0.05 lb/MWh) airborne emissions of fuel cell plants make them prime candidates for siting in urban areas. The possibility of using fuel cells in combined heat and power (CHP) units provides the cleanest and most efficient energy system option utilizing valuable (or imported) natural gas resources. Hydrocarbon fuel (natural gas or LNG) or gasified coal is reformed first to produce hydrogen-rich (and sulphur-free) gas that enters the fuel cell stack where it is electrochemically “burned” to produce electrical and thermal outputs. The electrical output of a fuel cell is low-voltage high-current dc. By utilizing a properly organized stack of cells and an inverter, utility-grade ac output is obtained. Early MW-scale demonstration plants employed phosphoric acid fuel cells. Molten carbonate fuel cell systems have shown considerable promise in recent years with demonstrated efficiencies in the 50 to 55% range based on the higher heating value. Another competitor in the long range is the solid oxide fuel cell that can be intergrated with a coal gasifier and a steam bottoming cycle. Solar-Thermal-Electric Conversion The quality of thermal energy needed for DG employing solar-thermal-electric conversion necessitates concen￾trated sunlight. Parabolic troughs, parabolic dishes, and central receivers are used to generate temperatures in the range of 400 to 500, 800 to 900, and >500°C, respectively. Technical feasibility of the central receiver system was demonstrated in the early ’80s by the 10-MWe Solar One system in Barstow, California. Over a six-year period, this system delivered 37 GWh of net energy to the