3.3 Concentrated solar power (CSP): How does it work?
Theoretically, concentrated solar power is one of the simplest renewable energy technologies. The term “concentrated solar power” generally refers to both concentrated solar thermal power (CSTP) and concentrated photovoltaics. To begin with, let us start our discussion from concentrated solar thermal power technology.
Concentrated solar thermal power plants convert solar energy into heat of a working fluid and the heat is then converted into electricity. A typical concentrated solar thermal power plant employs mirrors or reflectors to focus solar radiation onto a small surface area where a working fluid has been enclosed. The fluid absorbs heat from focused solar radiation and channeled into a steam generator which turns a steam turbine and generates electricity.
There are several types of concentrated solar thermal power plants in operation. The key difference among them is that they employ different types of reflectors. But they all (except concentrated photovoltaics) share almost the same concept to convert heat into electricity: It is nothing but a steam-powered electric generator!
As we discussed in the previous article, several configurations of concentrated solar thermal power plants have been developed and some of them have been employed in commercial-scale.
Among them, followings are the most common configurations.
- Parabolic dish concentrator
- Parabolic trough
- Linear Fresnel
- Central receiver tower
In addition to above, several other configurations are available to concentrate solar radiation. However, most of them are not economically/ technically viable and thus have not yet been used to generate electricity in commercial-scale. So, let us concentrate our discussion on potential concentrated solar thermal power concepts only.
1. Parabolic dish concentrator
Figure 01: Parabolic dish concentrators with Stirling engines
These systems use parabolic dishes to concentrate solar radiation onto its focal point. The paraboloid is the three-dimensional counterpart of a two-dimensional parabola. A typical parabolic dish system employs a heat receiver (At its focal point) coupled with a Stirling engine to collect heat. Collected heat is then channeled into the Stirling engine which exploits the heat to generate electricity. Their dual-axis solar tracking systems always track the Sun’s path and guide the dish so that the full aperture of the dish is always exposed directly to sunlight. The unique and intrinsic configuration of these systems allows to achieve even over 1000 ˚C and offers the highest conversion efficiency over other concentrating solar power systems. An annual efficiency of 16-18% has been already demonstrated with parabolic dish systems . However, these systems are still too expensive for commercial electricity generation.
2. Parabolic Trough Systems
Figure 02: A parabolic trough reflector
The parabolic trough reflectors look like a parabola in the X-Y plane as shown in figure 03. Their three-dimensional design produces a linear focus along the Z-axis along which a heat absorbing tube runs. The absorbed heat is used to produce steam which turns a turbine connected to an electric generator. The demonstrated annual efficiency for this technology is 10- 15% .
Figure 03: Diagram of a parabolic trough system
This technology is technically feasible and economically cost-effective compared to other concentrating solar power technologies and therefore, parabolic trough technology is today’s most popular concentrating solar thermal technology.
In the next article, let’s discuss some other concentrating solar power technologies.
 Müller-Steinhagen, H., & Trieb, F. (2004). Concentrating solar power. A review of the technology. Ingenia Inform QR Acad Eng, 18, 43-50.
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