The present paper looks into various issues concerning solar energy, such as main solar radiations, PV capacity, Concentrated Solar Power (CSP) technologies and energy storage materials, among others.
Main Solar Radiations
Solar radiations entail the electromagnetic radiations emitted by the sun, with the three main types including ultraviolet radiation, infrared radiation and visible light (Rahim et al., 2012).
Pyranometer
A typical pyranometer, which consists of a white disk for constraining acceptance angle to 180 degrees and two concentric hemispherical transparent covers made of glass, is mostly used in not only measuring the global solar irradiance incoming from a 2 π solid angle on a planar surface, but also the diffuse solar irradiance (Gd) provided that the contribution of the direct beam is eliminated (Rahim et al., 2012).
Installed PV Capacity
Available statistics demonstrate that Germany is the world’s top country in terms of installed photovoltaic (PV) capacity, with 7.6 gigawatts (GW) of newly connected systems (Mason et al., 2013).
LCOE
This abbreviation means the Levelized Cost of Energy, and is typically used to compare the cost of solar generated electricity produced by alternative means such as PV technology against electricity generated using traditional sources to come up with the price at which energy must be traded to break even over the lifetime of the technology (Branker et al., 2011). The LCOE has embedded assumptions, including “Direct Normal Irradiance (DNI) and meteorology of a particular location, as well as more general assumptions about the life of a plant and construction period, interest rate, and capital and operating rates” (Hinkley et al., 2011 p. 5).
Concentrated Solar Power (CSP) Technologies
Owing to the fact that nearly all of the world’s electricity is generated by first heating a fluid, CSP technologies denote yet another means of generating a hot fluid by focusing the radiation either along a line or at a point, which can then be used downstream in conventional power generation equipments such as steam turbines or stirling engines (Hinkley et al., 2011).
Most Mature CSP Technology
Among the known CSP technologies (e.g., Parabolic Trough, Fresnel Reflector, Solar Tower and Solar Dish), the Parabolic Trough is the most commercially viable CSP technology and is based on parabolic mirrors that concentrate the sun’s rays on heat receivers located on the focal line (IEA-ETSAP and IRENA, 2013).
Shams I CSP Plant
The electric power of the Shams 1 CSP plant, which is located in the United Arab Emirates and uses the Parabolic Trough CSP technology, is 100MW (IEA-ETSAP and IRENA, 2013).
Thermal Energy Storage Technology
Most commercial CSP plants use molten salt at 550°C for either heat transfer or energy storage purposes, as high-temperature molten salt has been shown to enhance both plant efficiency (e.g., 15%-17%) and thermal storage capacity. Available literature shows that most commercial CSP plants in Spain and the United States using synthetic oil as the transfer fluid and molten salt as the thermal energy storage technology are able to achieve a thermal storage capacity of around 7.5 hours, not mentioning that they can substantially improve the storage performance as well as raise the capacity factor by up to 50 percent (IEA-ETSAP and IRENA, 2013).
Different Storage Materials used in CSP Plants
The three storage materials mostly used in CSP plant in the United States and other developed and developing countries include molten salt, steam-based thermal storage and ammonia-based storage system. While the thermal capacity of molten salt has the potential to facilitate more storage capacity with substantially diminished storage volume and costs, hence enabling efficient and cheap heat storage as well as the use of efficient supercritical steam cycles, steam-based thermal storage is known to eliminate the need for a heat exchanger between the primary heat transfer fluid and the steam cycle. However, steam-based thermal storage is more challenging to use as it is substantially constrained by the use of steam and the high cost of pressure vessels. Ammonia-based thermo-chemical storage systems are particularly effective in CSP plants using the Big Dish technology, though they are still in their developmental phases (IEA-ETSAP and IRENA, 2013).
Advantages of CSP Technologies over PV
CSP technologies are able to achieve higher operating efficiencies and lower investment cost than PV as most of the technologies produce electricity by reflecting sunlight via solar collectors to heat a receiver to higher temperatures, before using turbines or stirling engines to transform this heat into mechanical energy and then to electricity. Additionally, unlike PV technology, CSP technologies employ an inherent thermal storage capacity that facilitates sustained power generation during cloud cover or after the sun goes down. It has also been documented that most CSP technologies are able to achieve a better hybrid operation capacity with other thermal storage fuels to successfully meet the base-load demand during the night. Most of the available PV technologies do not have this capability. In broader economic terms, CSP plants are known to create more job opportunities for local populations than PV technologies. Lastly, CSP technologies have the capacity to assist in the development of existing local industries, hence making them a rational choice in addressing the world’s energy crisis and fulfilling their renewable energy objectives (Mints, 2011).
References
Branker, K., Pathak, M.J.M., & Pearce, J.M. (2011). A review of solar photovoltaic levelized cost of electricity. Renewable & Sustainable Energy Reviews, 15(9), 4470-4482.
Hinkley, J., Curtin, B., Hayward, J., Wonhas, A., Boyd, R., Grima, C…Mikhail, A. (2011). Concentrating solar power – drivers and opportunities for cost-competitive electricity. Web.
IEA-ETSAP and IRENA. (2013). Concentrating solar power technology brief. Web.
Masson, G., Latour, M., Rekinger, M., Theologitis, I.T., & Papotsi, M. (2013). Global market outlook for photovoltaics 2013-2017. European Photovoltaic Industry Association. Web.
Mints, P. (2011). Smoke and mirrors: The argument about who wins – PV, CSP, or CPV – is currently all the rage. But is this just an unnecessary distraction? Renewable Energy Focus, 12(1), 42-46.
Rahim, M., Yoshino, J., & Yasuda, T. (2012). Evaluation of solar radiation abundance and electricity production capacity for application and development of solar energy. International Journal of Energy & Environment, 3(5), 687-700.