13 Jun 2012
Solar Power Plants
Article by E Lopes
Solar Power plants, or power stations, have been around for a few decades, and unlike traditional power plants they provide an environmentally benign source of energy, producing virtually no emissions, and consuming no fuel other than sunlight.
Traditional solar power plants are concentrating solar thermal plants, but more recently multi-megawatt photovoltaic plants have been built, namely those in Portugal and Germany. These are marking a trend toward larger photovoltaic power stations in different locations on the planet.
An advantage of solar thermal power plants is that they can generally be built in a few years because they are built almost entirely with modular, readily available materials. Another advantage is that while all power plants require land and have an environmental impact, the best locations for solar power plants are deserts or other land for which there might be few other human uses.
Solar thermal plants achieve the high temperatures required through concentration of solar radiation. Parabolic troughs, the most advanced technology for doing this, are very extensive and are made of shaped mirror segments. These troughs track the sun over the course of the day and focus the resulting radiation along the caustic line of the mirrors onto specially coated, evacuated absorber tube receivers. The solar radiation heats up the thermo-oil that flows through the receivers to a temperature of 400? Celsius so that a downstream heat exchanger is able to generate steam. The stream is pressurized inside the turbine that drives the generator. Heat storage systems can allow electricity output even if the sun isn’t shinning.
Solar dishes systems use concentrating solar collectors that track the sun, which means they always point straight at the sun and concentrate the solar energy at the focal point of the dish. A solar dish’s concentration ratio is much higher than a solar trough’s, and the power generating equipment can be mounted at the focal point of the dish, which makes it well suited for remote locations. As with a solar trough, the energy may be collected from a number of installations and converted to electricity at a central point. The engine in a solar dish system converts heat to mechanical power by compressing the working fluid when it is cold, heating the compressed working fluid, and then expanding the fluid through a turbine or with a piston to produce work. The dish is couple to an electric generator to convert the mechanical power to electric power.
A solar power tower or central receiver generates electricity from sunlight by focusing concentrated solar energy on a tower mounted heat exchanger (receiver). This system uses hundreds of thousands of flat sun tracking mirrors called heliostats to reflect and concentrate the sun’s energy onto a central receiver tower. With this system energy losses from thermal-energy transport are minimized as solar energy is being directly transferred by reflection from the heliostats to a single receiver. Solar power towers must be large to be economical, but this is a promising technology for large-scale grid-connected power plants.
Another solar technology for power plants is photovoltaic. The photovoltaic cells convert the sunlight directly into electricity. Photovoltaic cells, or PV cells, are made of semiconductors such as crystalline silicon or various thin-film materials. Thin-film materials are far less expensive and much less fragile, even if they are less efficient.
Solar power plants can have high installation costs, although these have been decreasing with the development of the technology, which is one of the reasons developing countries have started to build solar power plants to replace other sources of energy generation. At the pace the change is taking place it is believed solar power could become the dominant energy source within a few decades.
About the Author
The author has a website about solar energy. You can visit it at http://www.getsolarquick.com
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