Availability of energy storage and reconversion for later use Potential and Future Globally, the potential for DG is vast. Even extremely site-specific resources such as tides, geothermal, and small hydro are available in significant quantities. Assessments of the future for various DG technologies vary, depending on the enthusiasm of the estimator. However, in almost all cases, the limitations are economic rather than technical Concerns over the unrestricted use of depletable energy resources and the ensuing environmental problems such as the greenhouse effect and global warming are providing the impetus necessary for the continued development of technologies for DG. Motivation Among the powerful motivations for the entry of dg are: Less capital investment and less capital at risk in the case of smaller installations Easier to site smaller plants under the ever-increasing restrictions Likely to result in improved reliability and availability Location near load centers decreases delivery costs and lowers transmission and distribution losses In terms of the cost of power delivered, DG is becoming competitive with large central-station plants, especially with the advent of open access and competition in the electric utility industry DG Technologies Many technologies have been proposed and employed for DG Power ratings of DG systems vary from milliwatts to megawatts, depending on the application. a listing of the technologies is given belot Wind-electric conversio Tidal and wave energy conversion Solar-thermal-electric conversion Biomass utilization Thermoelectrics Thermionics Small cogeneration plants powered by natural gas and supplying electrical and thermal energies The technology involved in the last item above is mature and very similar to that of conventional thermal power plants and therefore will not be considered in this section. PV refers to the direct conversion of insolation(incident solar radiation)to electricity. A PV cell (also known a solar cell) is simply a large-area semiconductor pn junction diode with the junction positioned very close to the top surface. Typically, a metallic grid structure on the top and a sheet structure in the bottom collect the minority carriers crossing the junction and serve as terminals. The minority carriers are generated by the incident photons with energies greater than or equal to the energy gap of the semiconductor material. Since the output of an individual cell is rather low(1 or 2 W at a fraction of a volt), several( 30 to 60)cells are combined to form a module. Typical module ratings range from 40 to 50 w at 15 to 17V PV modules are progressively put together to form panels, arrays(strings or trackers), groups, segments(subfields), and ulti mately a Pv plant consisting of several segments. Plants rated at several Mw have been built and operated fully e 2000 by CRC Press LLC© 2000 by CRC Press LLC • Remoteness from conventional grid supply • Availability of energy storage and reconversion for later use Potential and Future Globally, the potential for DG is vast. Even extremely site-specific resources such as tides, geothermal, and small hydro are available in significant quantities. Assessments of the future for various DG technologies vary, depending on the enthusiasm of the estimator. However, in almost all cases, the limitations are economic rather than technical. Concerns over the unrestricted use of depletable energy resources and the ensuing environmental problems such as the greenhouse effect and global warming are providing the impetus necessary for the continued development of technologies for DG. Motivation Among the powerful motivations for the entry of DG are: • Less capital investment and less capital at risk in the case of smaller installations • Easier to site smaller plants under the ever-increasing restrictions • Likely to result in improved reliability and availability • Location near load centers decreases delivery costs and lowers transmission and distribution losses • In terms of the cost of power delivered, DG is becoming competitive with large central-station plants, especially with the advent of open access and competition in the electric utility industry DG Technologies Many technologies have been proposed and employed for DG. Power ratings of DG systems vary from milliwatts to megawatts, depending on the application. A listing of the technologies is given below. • Photovoltaics (PV) • Wind-electric conversion systems • Mini and micro hydro • Geothermal plants • Tidal and wave energy conversion • Fuel cells • Solar-thermal-electric conversion • Biomass utilization • Thermoelectrics • Thermionics • Small cogeneration plants powered by natural gas and supplying electrical and thermal energies The technology involved in the last item above is mature and very similar to that of conventional thermal power plants and therefore will not be considered in this section. Photovoltaics PV refers to the direct conversion of insolation (incident solar radiation) to electricity. A PV cell (also known as a solar cell) is simply a large-area semiconductor pn junction diode with the junction positioned very close to the top surface. Typically, a metallic grid structure on the top and a sheet structure in the bottom collect the minority carriers crossing the junction and serve as terminals. The minority carriers are generated by the incident photons with energies greater than or equal to the energy gap of the semiconductor material. Since the output of an individual cell is rather low (1 or 2 W at a fraction of a volt), several (30 to 60) cells are combined to form a module. Typical module ratings range from 40 to 50 W at 15 to 17 V. PV modules are progressively put together to form panels, arrays (strings or trackers), groups, segments (subfields), and ulti￾mately a PV plant consisting of several segments. Plants rated at several MW have been built and operated successfully