As the world grapples with the urgent need to combat climate change and meet the ambitious net-zero emissions targets by 2050, countries across the globe are decarbonizing their power grid using renewable energy sources. Of the many renewable energy sources available today, solar energy is a promising option because of its abundance and scalability.

Concentrating solar power (CSP) systems are essential technologies helping to harness the power of the sun to meet growing energy demands while significantly reducing greenhouse gas emissions. By utilizing mirrors and lenses to focus sunlight, CSP systems can generate heat, which can be used for industrial heating applications or combined with turbines to generate electricity.

However, while seemingly simple in operation, there is more to CSP systems than meets the eye. For instance, there are several types of CSP systems with different operating principles and suitability for different application requirements. Therefore, understanding CSP technologies is necessary for engineers looking to use them for their projects.

Figure 1: Concentrating solar power (CSP) systems are essential technologies helping to harness the power of the sun to meet growing energy demands Source: Eyal Shtark/Adobe Stock

Types of CSP technologies

CSP systems can be broadly categorized into four main types: parabolic trough, linear Fresnel, power tower and dish-Stirling collectors.

#1 Parabolic trough collector

Parabolic trough collectors are the most developed CSP technologies. As its name suggests, a parabolic trough collector features a parabolic mirror that focuses incident sunlight onto a receiver placed along the parabola’s focal line. The receiver is typically made of an absorber tube and a glass cover.

Figure 2: A parabolic trough collector features a parabolic mirror that focuses incident sunlight onto a receiver placed along the parabola’s focal line. Source: Kjkolb/CC-SA 3.0

The absorber tube contains the heat transfer fluid (usually thermal oils or molten salt) that gets heated by the concentrated sunlight from the parabolic mirror. This hot fluid transfers the heat to a heat exchanger, generating steam to power a turbine and produce electricity.

#2 Linear Fresnel collector

The linear Fresnel collector (LFC) features multiple flat mirrors arranged in a linear fashion, with each mirror tilted at a specific angle to track the sun’s movement throughout the day. As the mirrors track the sun, they reflect and concentrate sunlight onto a receiver located above the mirrors.

The receiver system in the LFC comes in different types, such as the receiver tube (similar to the one used in parabolic trough collectors), heat absorbing plates, and receiver panels, all of which help to absorb the solar energy and transfer it to the working fluid. The choice of receiver system depends on the desired operating temperature, thermal efficiency, and specific application. For instance, LFCs with receiver tubes are often used for moderate operating temperatures of around 400° C, while heat-absorbing plates are more commonly used to achieve higher operating temperatures and handle higher thermal loads.

#3 Power tower

A power tower (PT) system is quite similar to the LFCs in the sense that it employs an array of mirrors to reflect and concentrate sunlight onto a receiver. However, unlike LFCs, a PT system is a point focus system. This means its mirrors are arranged so that they reflect the sunlight onto a single point where the receiver is located.

PT systems are capable of achieving high operating temperatures, typically above 500° C and sometimes exceeding 1,000° C. This makes them suitable for applications that require high-temperature heat, such as advanced power cycles and solar fuel production.

#4 Dish-Stirling

Dish-Stirling systems feature a large dish-shaped mirror, which focuses sunlight onto a receiver. The receiver absorbs the heat energy and transfers it to a working fluid within a Stirling engine.

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Understanding the area concentration ratio in CSP systems

The concentration ratio is an important parameter used in designing CSPs. It represents the degree to which the incoming sunlight can be focused or concentrated on the receiver. It can be calculated using:

Eq4

Where:

A_a = area of the mirror aperture

A_r = area of the receiver

Engineers typically want to design their CSP systems to have a high concentration ratio (larger mirror aperture area compared to receiver area). However, achieving a high concentration ratio can also present challenges. For instance, it requires precise alignment and tracking of the sun to ensure an accurate reflection of the incident ray onto the receiver.

Conclusion

CSP technologies are paving the way for harnessing solar energy to produce heat and generate electricity. While this article presents the basics of the different types of CSP technologies, there are several other things to consider when choosing one for a project. Therefore, it is recommended to reach out to CSP manufacturers to discuss specific application requirements.