Concentrated Solar Power – How CSP Plants Work

Concentrated solar power is one of the most promising technologies for converting solar radiation into electricity in an efficient and sustainable manner. As the world urgently transitions towards cleaner energy sources, this technology is gaining attention for its ability to generate large-scale, reliable renewable electricity—especially in areas with high solar irradiance. The United Kingdom, although not ideally suited for CSP deployment due to its climate, still shows strong interest in the development and understanding of this solution as part of its wider energy strategy. Understanding how mirror-based CSP plants work, and why they represent a pivotal innovation, is key to envisioning a resilient and low-carbon future.

Unlike traditional photovoltaic (PV) panels, concentrated solar power systems use optical devices—primarily mirrors or lenses—to concentrate sunlight onto a specific point or line. This concentrated light is converted into heat, which is then used to generate electricity via a conventional thermal cycle, similar to that of a fossil-fuel power station. This thermodynamic method enables energy storage, offering a significant advantage: the ability to generate electricity even when the sun is not shining. For this reason, CSP plants are considered one of the few solar technologies capable of delivering dispatchable power—electricity available when needed.

What Is Concentrated Solar Power?

Concentrated solar power (CSP) is a renewable thermal energy technology that uses sunlight to generate heat, which is subsequently converted into electricity. Mirrors or lenses are used to focus sunlight onto a receiver, which heats a transfer fluid—typically oil or molten salts. This thermal energy is then used to create steam, which drives a turbine connected to a generator.

What makes CSP distinct from photovoltaic systems is that it doesn’t convert sunlight directly into electricity. Instead, it follows a process similar to that of a thermal power station, minus the fossil fuels. Because the heat is captured from the sun rather than from combustion, CSP can be integrated more readily into existing thermal infrastructure. This makes it a strategic tool for countries seeking a structured transition from fossil fuels to renewables.

Main Types of CSP Plants

There are several CSP technologies, each with unique configurations, efficiency levels, and cost structures. However, all rely on the same basic principle: concentrating solar energy using optical systems. The most widely adopted types include:

Parabolic Trough Collectors

These are the most common CSP systems in operation globally. They use curved mirrors to concentrate sunlight onto a linear receiver tube positioned at the focal line. A heat-transfer fluid flows through the tube, absorbing heat and reaching temperatures of around 400°C (750°F). The heat is then used to generate steam for electricity production.

Solar Power Towers

In these systems, a field of flat mirrors, called heliostats, track the sun and reflect sunlight onto a central receiver atop a tall tower. This setup enables the heating of molten salts to temperatures exceeding 500°C (930°F), which boosts thermal efficiency and simplifies storage integration.

Parabolic Dish Systems

These involve a dish-shaped mirror that focuses sunlight onto a receiver at its focal point. The collected heat usually drives a Stirling engine or similar device. While these systems are highly efficient on a small scale, they are mostly used in decentralised or research applications.

Linear Fresnel Reflectors

Fresnel systems use flat, slightly curved mirrors aligned in rows to concentrate sunlight onto an elevated receiver. Though they offer slightly lower efficiency than parabolic troughs, they are cheaper and easier to construct, making them suitable for certain project conditions.

How CSP Plants Generate Electricity

A concentrated solar power plant operates through a defined chain of energy conversion. Initially, solar radiation is concentrated by mirrors or lenses onto a receiver. This concentrated energy heats a fluid—typically synthetic oil or molten salt. The resulting heat generates steam, which then powers a turbine connected to an electricity generator.

One of the greatest strengths of CSP systems lies in their thermal energy storage capability. Heat collected during the day can be stored in insulated tanks filled with molten salts, allowing the plant to produce electricity during the night or in cloudy conditions. This feature addresses one of the primary drawbacks of renewable energy sources: intermittency.

Moreover, because the system relies on steam turbines, many CSP plants can be adapted for hybrid use with gas, or connected to combined-cycle setups. This creates flexible systems that reduce fossil fuel use while ensuring a stable electricity supply.

Advantages of Concentrated Solar Power

CSP offers significant advantages, particularly in regions with strong direct solar radiation. First and foremost is its energy storage capability. Unlike PV systems, CSP plants can store heat for several hours, ensuring electricity generation even after sunset. This ability to dispatch energy makes CSP a key contributor to grid stability.

Secondly, CSP plants—especially tower systems—can operate at high thermal efficiencies, allowing more of the captured solar energy to be converted into useful electricity. In addition, many components used in CSP facilities are recyclable, reducing the environmental footprint.

Another benefit is land usage. CSP systems can be installed on arid or unproductive land, avoiding competition with agriculture. Furthermore, dry cooling options exist for CSP plants in water-scarce areas, reducing the overall environmental impact.

Challenges and Limitations

Despite its potential, concentrated solar power faces several challenges. One of the most significant is high capital cost. Building a CSP plant requires substantial investment in mirrors, receivers, and thermal storage systems. Although costs have decreased, they still exceed those of other renewable technologies like PV or onshore wind.

CSP also depends heavily on direct normal irradiance (DNI), meaning it performs poorly in areas with frequent cloud cover or high humidity. This geographical limitation restricts CSP deployment to sunnier parts of the world.

The technology is also complex. CSP plants involve sophisticated optical, mechanical, and thermal systems that require specialised knowledge for installation, operation, and maintenance. This increases operational costs and necessitates a highly trained workforce.

Successful Projects Around the World

Several countries have successfully invested in CSP technology and are now global leaders. Spain was among the first to develop large-scale CSP, especially in Andalusia. Plants like PS10, PS20, and Gemasolar have demonstrated the effectiveness of thermal storage and round-the-clock solar generation.

Morocco has made substantial strides with the Noor Solar Complex in Ouarzazate, one of the largest solar installations worldwide. It meets a significant portion of Morocco’s electricity needs and has potential for cross-border power exports.

In Latin America, Chile has led CSP adoption with the Cerro Dominador plant in the Atacama Desert. It combines CSP and PV technologies to provide a well-balanced and continuous supply of renewable electricity.

Is There a Future for CSP in the UK?

The UK’s climate is not well suited for CSP deployment due to its relatively low levels of direct sunlight. However, CSP remains relevant for British energy strategy from a research and development perspective. UK-based companies and institutions are actively contributing to international CSP projects through innovation in storage materials, system design, and control algorithms.

Additionally, CSP could play a supporting role in decarbonising industrial processes worldwide—something the UK is investing in through international cooperation and green financing. While CSP may not become a core part of the domestic energy mix, it holds global strategic importance that aligns with the UK’s climate leadership goals.

Frequently Asked Questions (FAQ)

1. How does CSP differ from photovoltaic solar power?
CSP uses mirrors to generate heat from sunlight, which is then converted into electricity. Photovoltaics convert sunlight directly into electricity using semiconductors.

2. Can CSP produce electricity at night?
Yes. Thermal energy storage systems allow CSP plants to generate electricity hours after sunset by using stored heat.

3. What maintenance does a CSP plant require?
CSP systems need regular mirror cleaning, thermal system checks, and precise calibration of optical equipment. Skilled technicians are required.

4. Does CSP work in cloudy climates like the UK?
No. CSP depends on strong, direct sunlight. It’s most effective in dry, sunny environments and is not suitable for the UK’s weather conditions.

5. Can CSP support industrial decarbonisation?
Yes. High-temperature heat from CSP systems can be used in industrial sectors like cement and steel, offering a renewable alternative to fossil fuels.