Importance of Solar Energy - Term Paper Example

 Power Electronics strategies for Solar Power generation Introduction Solar power generation is the application of electronic or electrical technology to utilize naturally available energy from sunshine. In our world, naturally-occurring energy has become a phenomenon that needs to be utilized, precisely, the implications of unabated use of wholly artificial, environmentally-unfriendly methods of power generation presently available to us. However, technology’s positive aspects still exist, and if carefully applied and used appropriately with the natural sources, this will yield us to an ideal results even in an increasingly conservation-conscious or environmentally-sensitive world. This project therefore attempts a look at the means or methods that represent strategies that actually augur well in terms of successful generation of Solar power at the present time. The paper begins with a brief look at how solar technology works, i.e. how sunlight is converted into useful electricity and how this process can be harnessed. This includes a description of the photoelectric effect and how solar cells combine to form solar panels. This leads to a discussion of the efficiency of PV solar systems, how the efficiency can be increased, their power capacity and how the power can be maintained. Following this, the possibility of connecting the system to the utility grid is explored, mention is made of the importance and uses of solar powered systems in general, and long term strategies are considered for establishing solar systems more widely. How the technology works The way in which solar power technology works was explained in the October 20, 2008 issue of Scientific American (Locke). Sunlight is useful because it contains energy, and when this form of energy strikes an object, it generates heat. This can be demonstrated, for example by sitting in the Sun when we feel warm. However, when certain materials are struck by this same energy, electricity is produced instead. It is this process that can then be harnessed to generate electrical power from sunlight. Examples of such materials are silicon crystals, which are large and hard to grow and therefore expensive, and crystals made of copper-indium-gallium-selenide, which are smaller, thinner and cheaper although not as efficient. Such crystals are able to convert sunlight into electricity because the electrons in them “get up and move when exposed to light instead of just jiggling in place to make heat”. The interviewee Paul Alivisatos from the Helios Solar Energy Research Project explains further that the bonds between silicon atoms consist of shared electrons. When a photon, which is a packet of light energy, is absorbed, and an electron is sufficiently excited to a higher energy level making it freer to move around, the movement of that electron generates current. The phenomenon in which the absorption of photons of light leads to the release of electrons, is known as the photoelectric effect. The “direct conversion of light into electricity at the atomic level” is called photovoltaics (Knier, 2002). A simple illustration of the use of the photoelectric effect to produce current, i.e. the operation of a solar cell, is shown in fig. 1 below. Figure 1: The use of the photoelectric effect in a solar cell |(Source: Gil Knier) A solar cell is specially coated with a thin layer of semiconductor material such as silicon in order to generate an electric field. When sunlight enters on one side and electrons are knocked off inside the semiconductor, electrons are captured and the electrical conductors attached at the ends facilitate the flow of direct current (DC), which is then used to power a load. Small PV cells are already widely used, for example in wristwatches and calculators, but larger systems can power more things. A number of cells connected together to produce a specific voltage, typically 12V, is called a module, and modules can be further connected in an array to produce more electricity, as shown in fig. 2 below. Figure 2: Cell, module and array (Source: Gil Knier) Efficiency The term “efficiency” is the primary consideration in the operation of power electronic devices. Now, in Solar power generation, light from sunshine is converted by photovoltaic (PV) Solar panels into direct current (DC) electricity. In today’s world and in the future, in order to enhance Solar power generation, the aspect (efficiency) is an important consideration. Solar panels generally have a conversion ratio or Solar panel efficiency, which is an indication of their energy-conversion capability. For PV enhancement strategies, our design must include considerations that improve the current efficiency level of the PV, which can be estimated at a maximum of about 17.5% (Greenpeace, “Solar Generation”), and a minimum of 6% (IEA, “Renewables for Power Generation”). Also, to improve efficiency, we need to consider the thickness of crystalline silicon used in PV production; however needs to be carefully balanced against the desired increment in efficiency. This is due to the fact that efficiency tends to decrease with the thickness of the Silicon material. Perhaps some attention could be paid to optimising the spacing and inclination of PV panels (Geuder, Norbert et al). It might also help to look closely at enhancing PV efficiency through more focused use as ground receiver to capture maximum irradiation, with permanently varying solar angle (Geuder, Norbert et al). In a typical single junction PV cell, “only photons whose energy is equal to or greater than the band gap of the cell material can free an electron for an electric circuit” (Knier). In other words, in a single junction cell, the photovoltaic response is limited by the Sun’s spectrum; so lower energy photons do not get used. The efficiency of this process can therefore be improved by using multiple cells with different band gaps and multiple junctions. This arrangement of cells, wherein individual single junction cells are stacked together, forms a multi-junction cell, as shown in fig. 3 below. The top cell (Cell 1) with the highest band gap (Eg1) captures high-energy photons and lower cells (Cells 2-3) with lower band gaps (Eg2-3) capture lower energy photons. The conversion efficiency is higher because the multi-junction arrangement is able to transform more of the sunlight into electricity. Figure 3: A multijunction cell (Source: Gil Knier) In addition, it is an important aspect of power electronic-for-solar power strategy to consider the improvement of the absorption efficiency of the PV solar panels. An energy conversion loss is not acceptable in solar power generation, since there is relatively little power to waste. The largest PV plants have a capacity of just under 60MW. Power transfer losses may also be minimized by specifying the voltage capacity (Guidelines for Solar Power Generation) as a means of reducing availability of loss voltage. Power capacity The power capacity of PV solar panels can be improved in order to obtain the greater output in solar power generation. By paying close attention the weather, suitable operating conditions can enhance the power capacity. Further, by choosing an appropriate time of day, PV systems can receive optimal sunshine for conversion into electrical DC. Additionally, by carefully choosing the location of the PV array can improve the power output. Also, weather-proof designs need to be used more frequently on sites- these are naturally adaptable in size to the site, and can be installed very quickly. For example, this perhaps should suggest they can be utilized in such a way that follows the availability of sunlight, along with the simplicity of repeated setting-up at various sites. Tracking the maximum power operating point when solar irradiance levels and ambient conditions vary is a major design issue. The V-I characteristics tend to be non-linear so a DC-DC converter may be used to match with the load and operate at a maximum power point in addition to using an inverter to connect with the AC system. Bharati et al. thus suggested a cascaded H-bridge typology for serially connecting several panels, and a sinusoidal PWM for generating a sinusoidal terminal voltage and controlling its magnitude for connecting with the AC grid. The advantages of this configuration are that a step-up transformer and capacitors are not needed, the circuit is not so complex and filtering requirements are reduced. Grid connection Solar generated power can be used with grid (conventional) electricity through proper incorporation of power electronics. As less of conventional energy consumption is desired, less grid electricity will feature in mainstream power supply. Hence, hybrid systems can be improved, supported by the power electronics. The grid system can act as a storage system, so that it will receive excess power generated by the photoelectric systems during the day, then exporting the needed energy back into the PV system during nighttime, which is known as a shortfall period. This can be achieved through inverters, which converts DC to AC for the grid. For example, there can be significant increase of solar power generation; likewise stand-alone systems can benefit from Inverters and batteries applied for AC usage systems. The grid-connected PV systems need a wide range (Greenpeace, “Solar Generation”) of power classes to be properly adaptable to the flexibilities of grid power application. A PV system that is connected to the grid therefore has the following components (DOE), of which the first two are important and the third is optional: One or more PV modules (as per desired voltage) An inverter (to convert the solar power system’s DC to the grid’s AC) Batteries (for storing electricity or providing backup) A solar PV system connected to the grid is known as a ‘grid-tie solar system’ (GTS). In America, a permit is required before connecting a PV system to the utility grid and people can also install net metering. This allows the meter to spin backwards so that excess electricity can be supplied to the grid instead and for which payment or credit can be received. Besides, grid connected photovoltaic systems offer the advantages of both solar and conventional electricity supplies. The overall supply is likely to be more reliable and flexible than any one supply alone could be. An example of a grid connected PV system is shown in the diagram below. Figure 4: Grid connected PV system (Source: Pasolar) Importance and uses The main justifications for installing PV systems are to help preserve the limited and fast depleting fossil fuel based resources in the world, to prevent air pollution, and to be independent, or partially independent, from the utility companies. The environmental benefits are huge when we consider the destructive effects of using fossil fuels. Solar power is “ultra clean, natural and a sustainable source of energy” (Solar Power Notes). Solar power systems are used for supplying electricity to both domestic and commercial places. In contrast to non-renewable energy sources, solar power is in abundant supply and easily accessible. It is particularly useful where a connection to the grid is either not possible or would be too expensive such as in remote places. In this case, the system would be standalone without grid connection and therefore the need for an inverter. Common uses of solar power technology are the following: Producing solar electricity for general use For solar heating appliances such as hot water systems For solar cooling appliances For solar lighting appliances Solar power also has special applications such as in the space industry where it is known as spaced based solar power (Medin, 2010), and for seawater desalination (Glueckstern, 1995). Another big advantage for solar power is due to the free availability of sunlight. After the initial investment to set up a solar power system, the electricity supply will be free. It may take only a few years to recoup the costs after which there are clear economic benefits. Long-term strategies Long-term improvement of solar power generation through Power electronics will definitely depend on its market performance. There is a need to look into the high cost of PV modules. The design concept can be addressed such that thinner slices of silicon material are used in making the PV cells; hence a reduction in cost, as less production material is consumed. However, in our future design, a balance must be between decreasing the thickness and improving the efficiency of the cell. The thin film design option is known to have added advantages of lower weight and better appearance, which are good factors for customer appeal, and hence better marketability. Consumers of power generated from solar sources with the use of PV modules are presently faced with huge, discouraging upfront costs. This does not predict well for future development and improvement of Solar power generation through power electronics. Feed-in tariffs presently serve in some parts of the world to support the upfront costs. However, there is a need to strategise the feed-in-tariff in such a way that it becomes part of the regulation governing pricing the marketing of power electronics for solar energy. Market-viability for photovoltaic systems is also helped by separating cell and module production, since these require different levels of expertise, permitting assembly on location in places with end-use markets (IEA, “Renewables for Power Generation”). A long-term strategy by connecting numerous independent PV systems, together along with other renewable sources such as wind turbines, with the grid could also alleviate the need for conventional large power stations (Carrasco et al.). This kind of distributed energy system could be taking shape already as more and more people are creating their own solar systems, and could be the solution for future energy needs given the increasing demand for electrical power. Research on distributed energy systems by Hatziargyriou et al. suggested that microgrids can be created that would offer several economic and environmental benefits compared to the existing power systems. Solar PV systems could therefore play a major role in establishing such microgrids once the economic challenges of cost and technical challenges such as improving efficiency are overcome. Summary and conclusions Solar PV systems work by converting sunlight into electricity. Harnessing this process poses two main technical challenges: improving the efficiency and maintaining constant power. It was shown that efficiency can be improved by having more suitable panel characteristics and arranging cells more usefully. For example, multi-junction arrangements are more efficient than single junction cells. The importance of solar power will increase in the future because of the decreasing availability of fossil fuels to generate electricity and the deteriorating impact of using non-renewable sources on the environment. The main obstacle to using solar power generation at present is the huge initial investment required despite the fact that the electricity supply will then be free once a PV system is installed. However, this cost is likely to fall, as it already has done over the years, as demand increases. Ultimately, solar power PV systems will become the most preferred method for generating electricity (Bharati et al.). It is also possible to connect solar PV systems to the utility grid, which requires the use of an inverter for converting the system’s DC to the grid’s AC. When solar systems become more widely established, which is inevitable, they could potentially play a very important role in establishing distributed energy systems. Works Cited Bharati, Kamlesh Kumar; Samuel, Paulson & Gupta, Rajesh. “Solar energy conversion system using power electronics”. N.d. < http://www.mnnit.ac.in/departments/eed/iee_sem/sem_proced/vol1/Solar%20Energy%20Conversion%20System%20Using%20Power%20Electronics.pdf> 4 December 2010. Carrasco, J. M.; Franquelo, L. G.; Gialasiewicz, J. T. et al. “Power electronic systems for the grid integration of renewable energy sources: a survey.” IEEE Transactions on Industrial Electronics, Vol. 53, Issue 4, pp. 1002-1016. 2006. DOE. “A consumer’s guide: Get your power from the Sun”. U.S. Department of Energy. 2003. 4 December 2010. Geuder, Norbert et al, “Comparison of Solar Terrestrial And Space Power Generation for Europe” (4th International Conference on Solar Power from Space, SPS’04,30 June- 2 July 2004) http://www.climatetechnology.gov/stratplan/comments/Hoffert-1.pdf Glueckstern, P. “Potential uses of solar energy for seawater desalination”. Desalination, Vol. 101, Issue 1, pp. 11-20. 1995. Greenpeace, “Solar Generation” 12 April 2010 Guidelines for Generation Based Incentive for Grid Interactive Solar PV Power Generation Projects, No. 32/61/2007-08/PVSE , Govt. of India, Ministry of New and Renewable Energy 13 April 2010 Hatziargyriou, Nikos; Asano, Hiroshi; Iravani, Reza & Marnay, Chris. N.d. “Microgrids”. 4 December 2010. IEA, “Renewables for Power Generation”, 2003 . 14 April 2010 Knier, Gil. “How to photovoltaics work?” NASA Science News. National Aeronautics and Space Administration. 2002. < http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/> 4 December 2010. Locke, Susannah. “How does solar power work?” Chemist Paul Alivisatos explains how to generate electricity from sunlight. Scientific American, October 20, 2008. Medin, Kristin. “Disruptive technology: a space-based solar power industry forecast.” Online Journal of Space Communication, Issue No. 16. 2010. 4 December 2010. Pasolar. “Lesson 5: Photovoltaics (PV) system basics. “ N.d. 4 December 2010. Solar Power Notes. “Importance of solar energy.” N.d. 4 December 2010. Read More