7.2 Appropriate Selection of Solar Technology
From the entire range of solar technologies available, it is very important to select appropriate technology determined by the solar resources availability, type of applications, and space available for installations etc.
For water heating, industrial process heating, and drying application, the solar thermal technology is very appropriate. For instance, for low temperature applications with clear sky conditions, flat plate collector is appropriate whereas during overcast conditions, evacuated tube collectors may be more useful as they facilitate more efficient absorption of solar radiation, combined with excellent insulation provided by the evacuated tube. For applications where high–temperature process heat or steam is required, concentrating solar thermal technologies would be needed.
In the case of solar electricity generation, selection of appropriate technology is very important not only from the point of view of proper functioning but also from the point of view of maximizing economic benefits. Global solar radiation consists of direct and diffuse solar radiations. It is important to note that while solar thermal power plants can only use direct irradiance for power generation; photovoltaic systems can convert the diffuse irradiance as well. That means they can produce some electricity even with cloud-covered skies. The areas where photovoltaic systems and solar thermal power plants can operate overlap only in a narrow range.4Figure 7.22 illustrates the suitability of technology with respect to global solar radiation and power plant size.
Figure 7.22 Operational Areas for Solar Thermal Power Plants and Photovoltaic Systems Depending on the Installed Capacity and the Annual Global Solar Irradiation
Source: Contribution of Concentrated Solar Thermal Power for a Competitive Sustainable Energy Supply by Volker Quaschning; Norbert Geuder, Christoph Richter, Franz Trieb. http://www.volker-quaschning.de/downloads/CleanAir2003.pdf
Due to their modularity, photovoltaic operation covers a wide range from less than one watt to several megawatts. Moreover, photovoltaic systems can operate in stand-alone as well as in grid-connected mode. As explained earlier, there are different PV technologies but c-Si and thin film are most common. On the other hand in case of CPV, a few plants are under operation as pilot projects only.
Table 7.3 Selection of Appropriate PV Technology
One of the important factors in favor of thin film technologies is that they have better efficiencies with diffuse radiation. Therefore, where diffuse radiation component is high and skies are overcast, or if the PV is to be integrated with buildings with partial shading (or not facing the sun throughout the day), one can expect better annual energy output with thin film-based systems.
Concentrated solar technologies are more dependent on the DNI levels, hence the output and the profitability of solar thermal power plants is related to DNI levels of the locations. For economically viable systems, a minimum DNI of 5 kWh per sq m has been suggested. 5 Dish-Stirling systems are best suited for decentralized application with small capacity power requirements whereas the parabolic trough and solar tower power plants are best suited in the megawatt range.
For the CST plants, the selection of appropriate technology based on the application is listed in the following table.
Table 7.4 Selection of Appropriate Technology-based Application
As of now, the parabolic trough-based power plant technology has proved to be a mature technology, with the largest share in the installations among CSP worldwide. Even the first phase of Jawaharlal Nehru National Solar Mission (JNNSM) appears to have more parabolic trough-based CST plants coming up.
For the industrial heat application, compact LFR technology can be used because it is modular and its indigenization too could be faster.
4 Volker Quaschning et al. Solar Power–Photovoltaic or Solar Thermal Power Plants. Brussels: VGB Congress Power Plants 2001. 10-12 October 2001.
5 Siting guidelines for concentrating solar power plants in the Sahel: Y. Azoumahb et al. 2010. Case study of Burkina Faso. Solar Energy 84(8). Pp. 1545–1553. http://www.sciencedirect.com/science/article/pii/S0038092X10002100.