Abstract
In recent times, solar power has gained immense popularity due to its various advantages over conventional fossil fuels. It is clean, noise free and environment friendly. In the light of these advantages, it is important to study the various technologies used for harnessing the solar energy. This paper explores the various advantages and limitations of these methods in order to apply these for solar power generation.
- Introduction
As the global demand for energy is growing and environmental issues such as global warming assuming importance, the role of renewable energy sources in energy production is gaining popularity in recent times. Renewable energy sources are natural resources which can be sustainably replenished. Some examples are solar, wind, biomass, Geothermal, Hydropower, Tidal Energy, to name a few. Of all the renewable energy, solar power has gained immense popularity due to its various advantages and benefits. Contrary to the fossil fuels such as coal, solar power generation is clean, noise free and environment friendly. It does not produce harmful pollutants and greenhouse gases which lead to global warming endangering our planet. Another advantage of using solar energy is that it is free and abundant while fossil fuels are depleting and limited. Also no moving part is required in a solar panel, thus very less maintenance is needed to operate it.
In the light of above advantages of solar energy, it is important to study the various technologies used for harnessing the solar energy. Also the various advantages and limitations of these methods are to be studied in order to apply these for solar power generation.
- Solar Energy
2.1 What is Solar Energy?
Earth receives energy from the sun at a rate of 174 PW in the upper atmosphere. This is much larger than the total world energy consumption at present. Thus, solar power has emerged as an important alternative to the dominant energy sources such as fossil fuels. Solar energy is the energy harnessed from solar radiations with the help of photovoltaic (PV) technology. A PV cell contains a p-n junction, obtained by placing p-doped and n-doped semiconductors in contact. An electric field is built up at the interface, known as space charge region. This can be used for creating current with the help of electrodes.
Figure 1. PV Cell
The first PV cell was built by Gerald Pearson, Calvin Fuller and Daryl Chaplin (Bell Laboratories) in 1950s using silicon having an efficiency of only 6%. Since then, the technological progress in semiconductor industry has increased this efficiency to 25%.
2.2 Techniques for Solar Power Generation
There are several solar techniques available today. Each of them has its own advantages and disadvantages. Among all, the most widely used are Photovoltaic Silicon solar panels (PV), Concentrated Solar Power (CPS) and Solar powered Stirling Engine. These techniques can be applied on large scale, medium scale and small scale depending upon the application. A comparison between these technologies is presented in following subsections, which will help in deciding the adoption of most suitable and efficient technology given a specific set of conditions.
- Photovoltaic Silicon Solar Panels (PV)
Photovoltaic Silicon solar panels directly convert solar energy into electrical energy using PV cell. Because the amount of power produced by a single solar cell is relatively small, solar cells are connected together to form modules (panels) to generate a higher level of voltage, current, and power. Solar cells may be connected either in series to produce higher voltages or in parallel to produce more current. This kind of solar cell is called a crystalline silicon cell. Crystalline silicon solar cells generate direct electric current (DC), which is then converted to AC, usually with the use of inverters, in order to be distributed on the power network.
The biggest advantage of Photovoltaic silicon solar panels is their high efficiency ranging from 15% to as high as 25%. This make them as most widely used photovoltaic technology in the market as of today. Also they require less maintenance since no moving parts are required for their operation.
- Concentrated Solar Thermal systems (CSP)
Concentrated solar power, on the other hand, concentrates energy from sunlight to a heat receiver which transforms energy from heat into mechanical energy, and in turn, solar thermal electricity. The radiation of the sun is concentrated to heat a liquid substance such as water, which drives a heat engine and subsequently an electric generator [1]. This is shown in Figure 2. Alternating Current (AC) is generated by this method thus eliminating the use of inverters to convert DC to AC, as required in PV Solar Panel technology.
Figure 2. Concentrated Solar Thermal System
- Solar Powered Stirling Engine
Solar powered stirling engine consists of a small metal reflector, which focuses the sun's light energy on a special hydrogen filled tube. This results in rapid heating and cooling of the gas inside the tube which runs the sterling engine. This in turn can be connected to an electric generator to effectively produce electricity freely, cleanly and efficiently.
2.2.4 Comparison of PV Solar Panels vs. CSP
- Large Scale Power Generation
CSP systems use Thermal Energy Storage technologies to store energy, which is used in times of low or no sunlight to generate electric power. The use of TES increases the share of solar thermal technology in the energy sector. PV systems, on the other hand, directly generate electricity and do not store thermal energy especially at large scale power generation. Thus Concentrated Solar Thermal systems are more viable for large scale power generation. (Dominiki, [2]).
- Cost
PV systems can be built easier, at lower cost and at much shorter time than CSP plants, which need more space for large-scale applications. Also with substantial decrease in price of PV cells, the overall cost of PV system has been reduced by a large extent.
2.2.5 Comparison of PV Solar Panels vs. Solar powered Stirling Engine
Stirling engines are significantly more efficient at converting sunlight into energy than photovoltaic panels or CSP. These are four times more efficient than conventional PV solar panels. However, these are economically viable only for medium of large scale production i.e. 10 kW or more. For smaller scale generation, PV solar panels are preferred over solar powered Sterling Engine. Also solar power Stirling engines are expensive, unreliable and require extensive maintenance due to moving parts.
- Solar power generation on small scale (single household)
For single household scale, flat-plate PV module or panel is the most common array design used. These panels can either be fixed in place or allowed to track the movement of the sun. There are various advantages of fixed arrays such as no moving parts, no need for extra equipment and a lightweight structure. These features make them most suitable for residential roofs. However, since the panels are fixed in place, their orientation to the sun is usually at an angle that is less than optimal. Therefore, less energy per unit area of array is collected compared with that from a tracking array. This drawback, however, must be balanced against the higher cost of the tracking system [3].
- Conclusion
Till recently, most of the power is being generated using fossil fuels, which emit tons of green house gases leading to global warming. Also, fossil fuels are depleting and are limited. Thus, the role of renewable energy sources in energy production is gaining popularity in recent times. Out of various renewable energy sources, the solar energy industry is one of the fastest growing forces in the market because of the increasing demands in cleaner energy. Nowadays there are several techniques for solar power generation such as solar photovoltaic panels (PV), concentrated solar power systems (CSP) and solar powered Stirling engines, to name a few.
In order to choose the right solar system for a specific geographic location, it is very important to understand and compare the different solar technologies that are widely used. This paper not only gives a brief introduction about the most important solar technologies, but also a comparison of these techniques for different applications. This will help one in deciding adoption of most suitable and efficient technology given a specific set of conditions.
Refrences
1. http://www.processindustryforum.com/hottopics/advantages-and-disadvantages-of-solar-energy
2. Dominiki Faniou, Web document, http://www.renewablegreenenergypower.com/solar-energy-facts-concentrated-solar-power-csp-vs-photovoltaic-pv-panels/ (2013)
3. http://energy.gov/energysaver/articles/small-solar-electric-systems
Figures
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Figure 2
