Introduction
Modern human civilization is built on and continues to be principally dependent on large quantities of energy to sustain it. As from the 19th century, fossil fuels have been the primary sources of energy for man. However, owing to the population and exponential industrial expansion, these traditional sources of energy have been stretched to the limits as they aim to satisfy the global energy demands. In addition to these, it has in the recent decades been acknowledged that fossil fuels are largely responsible for adverse effects on the environment. A wider exploitation of renewable energy sources has been seen as the key to enhancing the energy security for many nations as well as mitigating environmental effects caused by fossil fuels. Governments have therefore begun to place emphasis on renewable energy sources such as wind, wave, ocean currents and solar energy. These sources are to act as alternatives to the use of existing oil and natural gas sources.
Solar energy in particular has been seen as a feasible cost effective and environmentally friendly source of energy. This paper will critically review large scale solar power production. The paper will argue that solar power is one of the most efficient renewable energy technologies which if fully utilized can lead to an end in the world energy need problems and mitigate the environmental hazards. The paper shall particularly focus on Concentrating Solar Power technologies which have emerged as the most economical and large scale deployable solar solutions in recent times. A detailed discussion of the advantages and disadvantages of this technology shall be given and compromises that may be achieved in its use proposed.
Solar Power: A brief Overview
Solar power is the energy that is harnessed from the sun’s radiation by use of a variety of technologies. Currently, solar technologies fall broadly under two categories; thermal and photonic (OECD/IEA 2006, p.3). Thermal technologies operate by first converting solar energy to heat and then translating the heat energy into some other usable form e.g. electricity by the use of mechanical devices. Photonic technologies on the other hand directly absorb the particles of light and convert them into electricity without complete conversion to heat energy. Traditionally, solar power has been used on a small scale to power electric bulbs in homes or even heat water; it is not until recent years that the concept of large scale production of solar electricity has been conceived and implemented.
The prevalent technology for large scale production of solar electricity is thermal solar technology (Department of energy 2001, p.1). The particular technology that is used to tap the sun’s energy is known as the concentrating solar Power (CSP) technology. While the sun’s raw radiation is adequate for heating surfaces, its density is not sufficient for electricity production therefore necessitating the concentrating process so as to increase the density (EC 2007, p.7.). For the solar energy to be harnessed for electricity production, its density has to be significantly increased. This is what is referred to as “concentrating” and it is achieved by the use of mirrors or lenses. CSP technologies are hailed as revolutionary since on maturity, they promise to deliver “green electricity” over an infinite period of time. Philibert (2004, p. 8) notes that CSP provides electricity in more or less the same manner that most technologies that make use of fossil and nuclear fuels do. That is by generating high temperature heat and then using this heat to operate a conventional power cycle e.g. a steam turbine which generates electric power that can be used by consumers.
CSP technologies can be categorized into three groups based on the concepts that they employ. The first category is troughs which is the CSP technology that uses parabolic trough-shaped mirror reflectors to concentrate sunlight. This sunlight is transferred to absorbent receiver tubes which contain a running fluid. The heat absorbs is used to heat the liquid producing superheated steam which is then used to run conventional turbines to produce electricity (EC 2007, p.9).
The second category known as Solar Towers is made up of a single receiver placed on top of a tower that is surrounded by numerous mirrors which redirect the sun’s light and focus it on the receiver (Sherif 2009). It is important to note that these mirrors, known as heliostats, are movable to enable them trace the motion of the sun across the sky throughout the day. The receiver absorbs the sun’s heat in a heat transfer fluid that passes through the receiver. This energy is then used to heat water so as to produce steam which is then used to generate electricity by use of conventional steam generators.
The third category is known as the Engine system and it uses parabolic dishes to concentrate the suns heat to a receiver. The receiver then absorbs the energy and transfers it to an engine which converts it to heat. The heat is converted to mechanical power in a manner seminar to conventional engines; that is by compression and rapid expansion of the fluid resulting in energy which turns a piston (DOE 2001, p.3). The mechanical energy provided by the piston is converted to electricity.
Advantages of Solar Power
The most significant advantage of CSP technology is as a result of it being a renewable source of electricity. This means that this source of power can be counted upon to last as long as the sun shines; which is for millions of years to come. This is unlike the traditional fossil fuel plants which are un-renewable and are therefore predicted to run out as demand increases. Since CSP technologies primarily rely on the sun for their fuel, they are relatively immune to fuel-cost fluctuations that are prevalent with power plants that rely on fossil fuels (Goerner, Muren & Gimon 2010, p.1).
Most Western nations do not have enough fossil fuel reserves to enable them to be self sufficient. As such, these countries are forced to rely on imports from regions such as the Middle East so as to fulfill their energy needs. CSP presents a means by which the energy security of a country can be guaranteed since a country can utilize its available solar resources to provide energy to either completely meet its energy needs or at least supplement the imports (Philibert 2004, p.22). This will lead to increased energy security for the nation and a significant decrease in foreign spending. As such, CSP will make it possible for countries which lack an abundance of fossil reserves to move towards self sufficiency in energy needs.
The power needs of most country’s are at the peak during the day time since this is when most industries are operational. Nersesian (2007) notes that this is one of the advantages of solar power since optimal levels of energy are attained during the day since this is the time at which the sun radiates most heat. This greatly increases the efficiency of CSP plants since the plant can cater for the energy demands sufficiently. The surplus energy generated during this high radiation periods can also be stored in molten salts and used to drive the turbines at night therefore decreasing the need for relying on fossil fuels to power the plant when the sun has disappeared.
In the recent years, environmental issues have taken a central place in man’s life mostly as a result of the global warming phenomena which is mostly blamed on fossil fuel emissions. Clean energy sources are therefore sought after so as to help retard the rate at which adverse climatic changes are taking place. CSP provides the best opportunities for large scale energy production with limited green house gas emissions. This is because CSP requires only the sun as its fuel and as such, little or no carbon emissions are released into the atmosphere. Philibert (2004, p.22) also notes that CSP technologies will lead to the more efficient use of natural resources which will lead to an improvement of local air quality as pollution is decreased to a bare minimal.
From a human resource perspective, Goerne, Muren & Gimon (2010, p.2) highlight that CSP plants have the potential to create hundred of thousands of new jobs for the county’s population. The authors estimate that 460,000 permanent jobs would be created if large scale CSP production were to be undertaken in the U.S. These projects would also lead to the creation of over 8million temporary jobs in construction and on completion; the plants would create a colossal 200 gigawatts of power. In light of the increase in unemployment levels in the recent years mostly as a result of the credit crunch in 2008, CSPs present a means by which a nation can provide a sustainable means of living for its population while at the same time reaping huge benefits in the form of sustainable electricity production.
Disadvantages of Solar Power
The most visible negative effect of CSPs is the huge amount of land that large scale production plants demand. Goerner, Muren & Gimon (2010, p.8) estimate that for a 177 MegaWatts Concentration Solar Power plant, 1 square mile of space is required. As such, significant tracks of contiguous land will be required for large scale power production to be achieved. In addition to the huge chunks of land that are demanded by solar powered stations, the large scale installations or mirrors have a negative effect on the ecosystem. This is because for large scale production of electricity to be achieved, CSP technologies require relatively large surface areas which house the arrays of solar collectors that are to be used for capturing the sun’s heat. The deployment of these structures leads to the shading or complete coverage of large tracts of land. The ecosystem that exists on these shaded surfaces will therefore be affected by the lack of sunlight.
Presently, solar technology is still significantly more expensive than traditional energy production means. The reason for this inflated cost is mostly as a result of the huge initial capital required to set up a solar energy producing plant since the technologies have not yet matured. This high cost is also brought about by CSP plant components which are mostly specialized products that must be custom made by manufacturers. In addition to the technological cost of these components, the raw materials required for these components e.g. steel, aluminum and glass are market driven and the rising global demand for these commodities has led to the increase in their cost therefore pushing the cost for CSP plant installation even higher. As such, most nations are unable to invest in CPS due to lack of financial and the technological knowhow. This is especially the case in the African continent which despite having huge thermal reserves, the capital needed to set up large scale CSP plants is prohibitive. Many governments therefore prefer to use the traditional energy sources which are cheaper and their technologies matured.
While solar power appears to be an attractive source of “free energy” which can be harnessed from the sun, the efficiency of the same cannot be guaranteed due to some natural phenomena. The presence of clouds leads to the scattering and absorption of solar energy before it reaches the earth’s surface therefore affecting the radiation received on a power plant. A report by the Organization for Economic Cooperation and Development (2006, p.3) concedes that the presence of clouds is the predominant atmospheric condition that determines the amount of solar energy available for conversion at any solar power station. This presents one of the biggest challenges for large scale solar power production since consistency and reliability must be guaranteed in such systems. The proneness of solar power to environmental conditions hugely disadvantages it since there are conditions that are beyond man’s control and in most cases cannot be accurately predicted.
CSP technology is to a high degree dependent on water. This water is used for running the turbines as well as cooling the plants. Access to water is therefore a major constraint in the deployment of CSP since most of these plants use water both as a working fluid, heat-transfer fluid and cleaning fluid for the collectors (OECD/IEA, 2006). This huge water needs is significant since most of the plants are built in desert regions where water supply is scarce. As such, the huge consumption of water leads to an increase in the overall production cost. In addition to these, the cooling water system discharges may contain toxic chemicals that are acquired as the water runs through the solar power pipe systems. These discharges if released into the environment can result in the disturbance of the ecosystem.
Solar power plants are characterized by huge reflective structures that are used to concentrate the suns rays. CPS plants can therefore interfere with air transportation systems. Aircraft operations in particular may be affected if reflected light beams become misdirected into aircraft pathways. While these can be avoided by ensuring that flight paths are directed away from CSP plants, accidental interferences could lead to catastrophic results on the airplanes. It is for this reason that most CPS installations are made in fairly remote regions.
Compromises in Solar Power
Radical advances can be made by engaging in more research and development efforts in solar technology. The DOE (2001, p.6) proposes that investing in Concentrating solar power technologies which offer the lowest cost solar electricity for large scale power generations could greatly decrease the net cost of a Kilowatt-hour of solar power. These advances which include invention of low-cost thermal storage will allow CSP plants to operate for more hours during the day and use the stored energy to run the solar power generation plant into the evening hours. As governments and other investors begin to see the huge benefits to be reaped from solar power, CSP technologies will slowly make their way to utility market and compete favorably with other power sources. Sherif (2009) notes that there has been a resurgence of interest in concentrating solar technologies in the last few years mostly as a result of new technical inventions made in the industry. In addition to these, governments such as the European Union have offered grants and subsidizes therefore leading to more investors venturing into solar power projects (EC 2007).
As it has been illustrated in this paper, one of the demerits of large scale production of solar power is the expansive land resources that such a project would require. However, Nersesian (2007, 316) notes that the land used for solar thermal systems compares favorably with that used for coal-fired plants when mining and storage area are taken into consideration. It can also be argued that most of the land that is used for solar power production is of limited economic value. This argument is reinforced by the fact that most of the areas of the world which have high thermal resources e.g. Southwestern US, the Tibetan plateau, and Northern Africa has sparse population and is far away from major cities. While this does pose as a problem since these areas are far from the regions which have a high demand for electricity, Philbert (2004) suggests that investments in high-voltage transmission lines which could be used to transport electricity over the long distances that exist between the production stations and high-demand regions would make the utilization of the high thermal resource areas feasible.
One of the core issues with solar power is that it cannot be tapped into 24hours a day as a result of the night and cloud interruptions. Philibert (2004, p.8) theorizes that while at the present CSP technologies have to be used in conjunction with fossil fuels, it may be possible in future to achieve heat storage which will open up the possibility of continuous solar only operations. The concept that CSP technology utilizes to achieve this is thermal storage whereby heat is stored in insulated tanks and used to run turbines at a later time. On maturity, this storage technology would lead to the overcoming of the problem of storage of electricity as current methods are only able to store electricity for limited durations. However, Goerner, Muren & Gimon (2010, p.2) articulate that thermal storage has not yet proven to be financially viable at commercial scales and more research is still needed.
In most cases, CSP technologies recycle the water they use leading to relatively reduced water usage. To avoid overreliance in water by the CSP technologies, technical advances are being made that allow dry cooling of the steam cycle which results in a dramatic 90% decrease in the usage of water as compared to the wet-cooled plants (Goerner Muren & Gimon 2010, p.8). This greatly decreases the cost of running solar power plants in places where water is scarce. In addition to this, environmental hazards that might occur as a result of toxic water spillage are alleviated making CSP technologies more eco-friendly.
Conclusion
The concept of concentrating solar power technology to produce electricity on a large scale is technically and economically feasible and offers the means by which the word’s power problems can be solved with little of no adverse effects to the environment. The biggest attraction that these technology offers is the ability to offer clean energy for an indefinite period thereby assuring the energy security of a nation. This paper set out to research on large scale solar power production so as to provide a deeper understanding of this technology. To this end, a detailed analysis of concentrating solar power technology has been undertaken. From the discussions presented in this paper, it is clear that this technology if extensively exploited harbors the capacity to provide for the energy needs of a country.
While solar power does have some disadvantages, it has been demonstrated that some of these demerits such as thermal storage and relatively high capital costs are as a result of the relatively young nature of the technology and one can therefore expect them to wane off as the technology matures. Bearing in mind the environmental costs of energy productions, it is clear that solar power is far superior to fossil fuels or even nuclear energy. Energy policies that seek to benefit the environment should therefore pay close attention to CPS on a large scale as this technology has the potential to provide enough energy supply to meet a nation’s demands with low environmental cost for an indefinite future.
References
European commission, 2007, concentrating Solar Power: From Research to Implementation, Belgium: European Communities.
Goerner T, Muren R & Gimon, E, 2010, Concentrating Solar Power, Web.
Nersesian, R, 2007, Energy for the 21st century: a comprehensive guide to conventional and alternative sources, M.E. Sharpe.
Organization for Economic Cooperation and Development/International Energy Agency (OECD/IEA), 2006, Solar Energy Potential on the U.S. Outer Continental Shelf, Web.
Philibert, C, 2004, International Energy Technology Collaboration and Climate Change Mitigation, International Energy Agency.
Sherif R, 2009, Concentrating Solar Energy- Technologies and Markets Overview, CS MANTECH Conference, Web.
U.S. Department of Energy (DOE), 2001, Concentrating Solar Power: Energy from Mirrors.