Solar Thermal Power The Basics-txc.cc

Home-Improvement SOLAR THERMAL POWER THE BASICS POWER FROM THE SUN The principles of solar thermal power conversion have been known for more than a century; its .mercial scale-up and exploitation, however, has only taken place since the mid 1980s. With these first large-scale 30-80 MW parabolic trough power stations, built in the California Mojave desert, the technology has impressively demonstrated its technological and economic promise. With few adverse environmental impacts and a massive resource, the sun, it offers an opportunity to the countries in the sun belt of the world .parable to that currently being offered by offshore wind farms to European and other nations with the windiest shorelines. Solar thermal power can only use direct sunlight, called beam radiation or Direct Normal Irradiation (DNI), i.e. that fraction of sunlight which is not deviated by clouds, fumes or dust in the atmosphere and that reaches the earths surface in parallel beams for concentration. Hence, it must be sited in regions with high direct solar radiation. Suitable sites should receive at least 2,000 kilowatt hours (kWh) of sunlight radiation per m2 annually, whilst best site locations receive more than 2,800 kWh/m2/year. Typical site regions, where the climate andvegetation do not produce high levels of atmospheric humidity, dust and fumes, include steppes, bush, savannas, semi-deserts and true deserts, ideally located within less than 40 degrees of latitude north or south. Therefore, the most promising areas of the world include the South-Western United States, Central and South America, North and Southern Africa, the Mediterranean countries of Europe, the Near and Middle East, Iran and the desert plains of India, Pakistan, the former Soviet Union, China and Australia. In many regions of the world, one square kilometre of land is enough to generate as much as 100-130 gigawatt hours (GWh) of solar electricity per year using solar thermal technology. This is equivalent to the annual production of a 50 MW conventional coal- or gas-fired mid-load power plants. Over the total life cycle of a solar thermal power system, its output would be equivalent to the energy contained in more than 5 million barrels of oil2). However, this large solar power potential will only be used to a limited extent if it is restricted by regional demand and by local technological and financial resources. If solar electricity is exported to regions with a high demand for power but few indigenous solar resources, considerably more of the potential in the sun belt countries could be harvested to protect the global climate. Countries such as Germany are already seriously considering importing solar electricity from North Africa and Southern Europe as a way of contributing to the long-term sustainable development of their power sector. However, priority should be given primarily to supply for legitimate indigenous demand. TURNING SOLAR HEAT INTO ELECTRICITY Producing electricity from the energy in the suns rays is a straightforward process: direct solar radiation can be concentrated and collected by a range of Concentrating Solar Power (CSP) technologies to provide medium- to hightemperature heat. This heat is then used to operate a conventional power cycle, for example through a steam turbine or a Stirling engine. Solar heat collected during the day can also be stored in liquid or solid media such as molten salts, ceramics, concrete or, in the future, phase-changing salt mixtures. At night, it can be extracted from the storage medium thereby continuing turbine operation. Solar thermal power plants designed for solar-only generation are ideally suited to satisfying summer noon peak loads in wealthy countries with significant cooling demands, such as Spain and California. Thermal energy storage systems are capable of expanding the operation time of solar thermal plants even up to base-load operation. For example, in Spain the 50 MWe AndaSol plants are designed with six to 12 hours thermal storage, increasing annual availability by about 1,000 to 2,500 hours. During the market introduction phase of the technology, hybrid plant concepts which back up the solar output by fossil cofiring are likely to be the favoured option, as in .mercially operating parabolic trough SEGS plants in California where some fossil fuel is used in case of lower radiation intensity to secure reliable peak-load supply. Also, Integrated Solar- .bined Cycle (ISCC) plants for mid- to base-load operation are best suited to this introduction phase. .bined generation of heat and power by CSP has particularly promising potential, as the high-value solar energy input is used to the best possible efficiency, exceeding 85%. Process heat from .bined generation can be used for industrial applications, district cooling or sea water desalination. Current CSP technologies include parabolic trough power plants, solar power towers, and parabolic dish engines (see Part Two). Parabolic trough plants with an installed capacity of 354 MW have been in .mercial operation for many years in the California Mojave desert, whilst solar towers and dish engines have been tested successfully in a series of demonstration projects. About the Author: 相关的主题文章: