The generation of electric power through the exploitation of fossil fuels, such as coal, oil and natural gas, is one of the main factors influencing climate change due to the greenhouse gases emissions resulting from the process. In consideration, there is an increasing need to shift towards systems of power generation derived from renewable sources, which have a significantly lower environmental impact; among these are solar, wind, geothermal, hydraulic and ocean power generation. This essay will focus on solar power generation.
The energy contained in sunlight can be converted into electricity through the use of Concentrated Solar Power systems (CSP) or photovoltaic cells (PV). According to Machinda, Chowdhury, Arscott and Kibaara, CSP systems depend on the concentration of sunrays onto Heat Transfer Fluids, which are heated and subsequently turned into super-heated steam that is used to drive a turbine or engine to generate electricity. These systems are categorized in line focusing systems, which use rectangular mirror configurations tilted towards the sun to collect its energy (such as Linear Fresnel Reflectors and Parabolic Trough), point-focusing systems based on dish-shaped mirrors similar to a satellite (Solar Dish systems), and solar tower systems, which according to the NREL, “use a large field of flat, sun-tracking mirrors known as heliostats to focus and concentrate sunlight onto a receiver on the top of a tower”.
Photovoltaic cells, on the contrary, directly perform the conversion of sunlight into electricity by taking advantage of the physical properties of semiconductor materials. Solar panels are arrangements of photovoltaic cells composed of semiconductors with p-n junctions that are used to concentrate sun rays, which upon striking the panel’s surface raise the energy level of the electrons freeing them from their atomic shells (Penick and Louk, 3), and these are then forced to move in one direction effectively establishing a flow of electrical current. Figure 1 shows a general diagram that explains how solar cells work. Crystalline silicon (c-Si) is the most widely used type of solar cell, followed by thin-film PV technology and concentrating PV arrays. The result of this process is in the form of direct current (DC), which goes through inverters that convert it into alternating current (AC), which is the standard in generation and distribution systems.
Figure 1. - How solar cells work from Penick and Louk; “Photovoltaic Power Generation”; December 1998
Photovoltaic power generation is implemented through solar farms, which are large-scale systems composed of many panels distributed among extensive fields, used to supply power to grids shared by multiple users or, conversely, through individual systems used to power specific homes or businesses, mostly through the installation of solar panels on rooftops.
The main concern regarding solar power generation is related to its dependence on incoming radiation and the limitation of electricity output by uncontrollable weather conditions, which can result in stability issues for the connected grid. Moreover, during nighttime, PV panels stop producing electricity altogether. For this reason, battery systems are used to store power which can be delivered when needed, aiding in the mitigation of frequency and voltage issues. Furthermore, panels, troughs, reflectors and mirrors are equipped with solar-tracking technology that allow them to tilt according to the position of the sun and angle of incoming radiation and maximize sunlight energy collection.
Solar power generation has environmental impacts related to land use, which raises concerns on land degradation and habitat loss, manufacture of PV components and use of hazardous materials; however, its Composite Environmental Impact Index (CEII) is 52.38, which is considerably lower than the environmental impact of coal-fueled power generation, rated at 885.48, according to Cichocki. Moreover, technologies to recycle materials at the end of their life cycle are under development.
The efficiency of solar power generation varies depending on the type of system used and according to IRENA, it ranges from 11-16% for parabolic trough systems, 7-20% for solar tower systems, 22-24% for linear Fresnel systems and 25-28% for dish-stirling systems. Solar-to-electrical conversion efficiency for PV technologies is, according to Penick and Louk, up to 15% for single-crystal silicon cells and approximately 8% for thin-film cells. These percentages may seem low when compared to thermal efficiency ratings of thermal power plants (approximately 40%), but given that they are based on a renewable primary energy source, they represent an environmentally-friendly way to generate electricity and are thus valuable in the fight against climate change.
Solar power generation is quickly growing: according to the Fondation Energies Pour Le Monde, it accounted for 0.5% of the electricity produced worldwide in 2012, but rose to an approximate 1% in 2015, mostly through PV technologies. This is likely due to the drastic fall of prices that have made solar more affordable both for residential and non-residential purposes, which has been of approximately 70% from 2008 to 201, even as solar panel technologies have become smarter (Nunez). However, electric billing for conventional energy has not experienced a similar fall, which is the reason why so many buildings and households are now at least partially covered by PV cell systems.
In conclusion, these systems provide sustainable green energy that help to slow global warming as their carbon footprints are considerably lower than those of conventional electricity generation methods, provide energy security and independence, and for those who implement individual systems in their homes, save money in the long-term. Therefore, countries should seek to replace fossil-fuel power generation for renewable sources of energy such as solar power.
References
Cichocki, Andrezej. "Solar energy: better than fossil fuels, worse than anything else." 2009. Environmental Impact Website. 13 April 2016.
International Renewable Energy Agency. Concentrating Solar Power. Working paper. Abu Dhabi: IRENA, 2012.
Machinda, G, et al. "Concentrating Solar Thermal Power Technologies: A Review." 2011 Annual IEEE India Conference. Ed. IEEE. Hyderabad, 2011. 1-6.
Monde, Fondation Energies Pour Le. "Electricity Production in the World: General Forecasts." 2013.
National Renewable Energy Laboratory. "Concentrating Solar Power Basics." n.d. NREL Website. Web. 13 April 2016.
Nunez, Christina. "Solar Energy Sees Eye-Popping Price Drops." 2 October 2015. National Geographic. Web. 12 April 2016.
Penick, Thomas and Bill Louk. "Photovoltaic Power Generation." 1998.
