Solar thermal power implies the direct heating of liquids or gases. Mainly water is used as the fluid for storing solar thermal power.Currently, some countries have developed power stations where solar thermal energy is being utilized along side the conventional photo voltaic cells.
Mechanism For Acquiring Solar Thermal Power
The basic idea is to converge sun rays on certain material to extract the heat from fluids at high temperatures. Different arrangements can be made for a manifestation of the idea. Many commercial buildings and homes have used the idea for water heating.
Design For Solar Thermal Power
For converging the sun rays solar thermal collectors are required. Solar thermal collectors can be divided into three categories according to temperatures. These are low, medium and high temperature collectors.The low temperature collectors are used for heating swimming pools or for space heating in large buildings. The medium temperature collectors are used to produce hot water for residential and commercial use.High temperature collectors are used in thermal energy plants. These temperature collectors employ the technique of concentrated solar power, for which there are quite a few ways.
Techniques For Concentrated Solar Power
The sun rays can be concentrated on the working fluid using power tower, parabolic reflector or parabolic trough.
Power Tower
In a power tower the mirrors tracking the sun surround an absorber tank on a tower in the middle of the array.
Parabolic Reflector
There can be a parabolic reflector that tracks the sun with its own absorber tank at the focal point of the dish.
Parabolic Trough Collectors
In parabolic trough collectors, there is a stationary curved mirror which extends in a linear way, with an absorber tube running along the focal point of the trough’s curved surface.
The sun rays thus have a great combined heating effect. The sun rays can be used to heat boilers, or a set of tubes, through which water is moving. The heating effect of the sun rays can be used to make super heated steam. This steam has the thermal energy which is converted to mechanical energy of a rotating turbine. This rotating turbine then converts the mechanical energy to electrical energy with the help of a generator.
The first generation of solar thermal systems was parabolic trough. Apparently, the most economical way of generating electricity from solar thermal power is using parabolic trough design. The design is not efficient as compared to others but it is the cheapest, since there is no need of tracking equipment. However due to low car not efficiency and reduced storage options it does not generate the same amount of electricity. As a whole, the power tower arrangement is believed to be the best in terms of long term gains.
Comparison with Photo voltaic Cells
The main method of producing electricity till now has been through photo voltaic cells. The photo voltaic cells have their own advantages. The photo voltaic cells directly convert solar energy to electricity. They have no moving parts. They are durable. And they do not create pollution. But, at least at present their costs are high. Solar thermal power is probably the most economical way to generate renewable energy. Solar thermal power systems can produce over 64 megawatt-years of electricity per square mile per year. By contrast, large-scale photovoltaic systems can produce about 93 megawatt-years per square mile per year.
Comparison With Wind
There is a great debate on the amount of land required for the construction of wind farms. The space required by wind turbines blades is huge. A safety zone of at least 5 acres is needed in addition to the space directly occupied by wind turbines. Roads are necessary to be built and transmission lines have to be laid for keeping the turbine operational. An area of about 30 acres surrounding the wind farm has to be cleared off from trees. According to some estimates, on average of 50 acres of land is required to produce just one megawatt of electricity.
Good news about solar thermal systems is that the amount of land they require to produce substantial amounts of electricity is not that great. Solar thermal power systems can produce over 64 megawatt per square mile and photo voltaic cells can produce 93 megawatt of electricity per square mile. It only takes about 950 square feet per person, an array 30′ x 30′, for solar thermal systems to replace 100% of the energy currently consumed by humanity. Land, clearly, is not the issue.
Comparison of Solar Thermal Power with Hydro
The space required by the dams is also great, although the space required per megawatt is significantly less than the other two renewable energy sources. The displacement of the population and disturbance of the eco system are very significant effects due to which the trend of development of hydro projects in developed countries is on a decline. The options to exploit the landscape for building dams are also depleting fast.
Advantages Over Bio fuel
Bio fuels are also a good option for renewable energy, but the crops required for acquiring bio fuel are not easily available. This is because the other crops pose a stiff competition for their growth. And the total area under cultivation on earth will more or less be the same. Solar power systems do not need any fuel except the sun rays, which are free of cost.
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