Explained: Concentrated Solar Power (CSP)

What is concentrated solar energy (CSP)?

Concentrated solar power (CSP), is a method of generating electricity using mirrors. Mirrors are used to reflect, concentrate, and focus sunlight on a point. This heat is then converted into electricity. The heat is used to make steam which can be used to drive a turbine to produce electrical power. CSP technology allows for the continuous production of heat. You can use it on days when there is no sunlight, before sunrise and after sundown.

According to the International Energy Agency, CSP production increased by 34% in 2019, according to the IEA. This is a remarkable increase, but CSP still has a long way to go before it reaches its Sustainable Development Goals. (SDGs) require an average growth rate of 24% between 2030 and 2025.

What is concentrated solar power?

CSP technologies employ a mirror structure that concentrates sunlight’s energy onto a receiver. The receiver then converts it into heat. The heat is converted to steam, which drives a turbine that generates electrical power. Thermal energy storage systems can be used by CSP plants to store power until it is needed. This is useful for when there is little sunlight. CSP is a flexible source for renewable energy because it can store energy.

CSP systems can be combined with other power sources in order to create hybrid power plant. CSP systems can also be combined with thermal-fired power stations that burn fuels such as coal, natural gas, and biofuel.

There are four types CSP technologies.

1. Parabolic-trough systems This system concentrates solar energy by using curved, trough-shaped reflectors that are directed onto a receiver tube. The pipe is usually filled with thermal oil. This oil is heated and used to produce electricity in a steam-generator.
2. Power tower system – These systems employ mirrors called Heliostats, which track the sun’s energy and direct it onto a receiver located at the top of a tower. The receiver heats a fluid, often molten salts, and it is used to create steam that drives a turbine generator.
3. Linear Fresnel Systems Large numbers of collectors are arranged in rows. Mirrors are placed flat on the ground to reflect the sun onto the receiver pipes above. Fresnel, similar to tower and trough systems, can be integrated into a power block or directly generate steam.
4. Parabolic dishes systems A parabolic dish acts as a concentrator and reflects solar energy onto the receiver mounted on a structure that has a tracking system that tracks the sun. A heat engine then generates the heat from the collected heat. This dish can reach very high temperatures which could make it suitable for solar reactors.

Concentrated solar power has many benefits

CSP’s greatest advantage is its renewable nature. CSP’s unlimited supply means that it can be used continuously and will not run out. This makes it a renewable energy source. It reduces the carbon footprint. CSP is more friendly to the environment than fossil fuels that emit carbon dioxide. It can increase the quality of the air and slow down climate change.

CSP provides electricity in a steady source, unlike solar photovoltaics and wind power which only provide intermittent supply. CSP plants are able to store solar energy as molten salts. This makes the electricity generated predictable and reliable.

CSP can easily be integrated into existing steam-based power stations. CSP can be used even in power plants that run on fossil fuels. Because of the simplicity of operations and maintenance, CSP plants are also less expensive than those that use nuclear or hydrocarbon-based fuels.

You can combine concentrated solar power with other energy sources to create a safer energy grid. CSP can be used in the electricity mix to meet future electricity demands. CSP can also be used to aid in oil recovery. The steam it produces can then be used to concentrate heavy oils, making it easier to pump.

It can also be used to transportable energy. Ecofys , a renewable energy consultancy, published a study to examine the feasibility of CSP as a technology for producing cost-effective hydrogen that could be used to power transportation.

Concentrated solar power has its disadvantages

CSP has its flaws, despite the many benefits. It is heavily dependent on the location. CSP plants, like solar PV or wind power, require large areas of land to function. This makes them uneconomical in densely populated areas.

Concentrated solar power requires a lot water to run steam turbines and cool thermochemical reactors. Seawater could be a solution but it can cause solar radiation problems for the landscape. CSP plants are also able to attract animals by their light. Some species can even die from the heat.

CSP plants can also be expensive to operate. It is difficult to find thermal energy storage materials that can withstand high temperature. Molten salt is one example. It solidifies at low temperatures, and breaks down at high temperatures.

CSP is not always able to compete with other energy sources such as solar PV or fission-based nuclear power. Concentrated solar power is at risk of being obsolete as other breakthroughs are made.

Concentrated solar power is how efficient?

There are many factors that affect the efficiency of a CSP system. How efficient a concentrated solar power system runs will depend on the type of system, engine, and receiver. EnergySage states that most CSP systems are between 7 and 25% efficient.

Hydropower systems can achieve efficiency of up to 90%, while wind turbines can achieve efficiency up to 59%. Concentrated solar power systems have similar efficiency levels to solar PV. Most photovoltaic cells achieve an efficiency between 14 and 23 percent.

Where is concentrated solar energy used?

According to NS Energy online publication, global CSP installations grew by 24%, from 765MW to 5.4GW between 2009 and 2018.

Spain is home to 42% of all CSP plants worldwide. Spain’s Planta Solar 10 (PS10) was the first commercial utility-scale, solar power tower. As part of a ten year energy plan, the country plans to double its CSP capacity to 4.8GW by 2025.

The Ouarzazate Solar Power Station in Morocco, with a capacity of 515MW, is currently the largest CSP project anywhere. It consists of three plants and was operational since 2016. It can provide power consumption of around 1.1 million Moroccans.

The rank of the Moroccan plant will be lost to Noor Energy1, Dubai’s 700MW CSP project. Although the plant doesn’t have an expected completion date, it is part of Dubai’s Vision 2021 initiative to promote sustainable and environmentally-friendly development.

USA is well-known for its CSP projects. The country currently has 52 plants. The largest of these being the 392MW Ivanpah facility located in California. Since 2016, however, there have not been any new CSP-related projects in the USA.

What is the difference in solar PV and concentrated sun power?

The way that electric power is generated is perhaps the most significant difference between solar PV systems and CSP. CSP systems convert sunlight’s energy into electricity using mirror configurations. These mirrors drive heat engines and generate electrical power.

Photovoltaic panels on the other side use the sun’s energy rather than the sunlight’s. CSP does not convert light directly to electricity. PV, however, does. The solar PV cells absorb sunlight (rather than reflect heat), and stimulate electrons to create current. Inverters convert the direct current (DC), into an alternating current, and distribute it on the power network.

CSP systems store energy using Thermal Energy Storage Technologies (TES), which allows power to be used even when there isn’t enough sun. However, PV systems can’t store thermal power because they only use direct sunlight and not heat. CSP systems, on the other hand, are more efficient in energy storage and efficiency.

Above: A CSP Solar Trough Collector used to generate solar energy

What environmental effects can concentrated solar power have?

CSP plants are often found in areas with limited water supply because they require large amounts of space. To cool the thermal cycle, wet cooling towers and water are needed. Water is also required to clean mirrors in order to maintain their reflectivity. These areas are often criticised for using large quantities of fresh water, particularly when there is increasing water demand in North Africa and the Middle East.

CSP plants also have a visual impact on certain areas. CSP plants are often criticized for their ability to obscure natural landscapes, which is a common criticism.

They are still important for their environmental value and offer habitats to threatened species, despite the absence of agriculture in the sun belt region. These areas are more dry than other regions, which means it takes longer for communities and the landscape to recover from disturbances. The infrastructure required to run a CSP plant can have a negative impact on animal populations.

CSP plants are more resource-intensive than traditional fossil-fired plants and many of these materials can’t be recycled. Concentrated solar power plants can also produce harmful substances such as biphenyl. These dioxins can remain in the environment for years and can cause severe health problems.

CSP plants are linked to greenhouse gas emissions because the nitrous sodium used in energy storage releases nitrous oxide (N20), a compound that damages the ozone layer.

Concentrated solar power plants can also negatively impact fauna and flora. Traffic routes and construction work can disrupt the ecosystem and lead to mortalities for local fauna.

What is the future for Concentrated Solar Energy?

The global solar industry has seen rapid growth in the last decade. However, concentrated solar power has made a significant impact. Solar Spaces reports that there are more than 130 CSP projects worldwide, with an installed capacity of 5,500MW.

CSP tariffs have fallen to a level that is lower than ever, but there are still many challenges for concentrated solar power. CSP plants can be expensive to build, operate and finance, making it difficult to raise funds for new projects. Research will drive down the cost of CSP and investors will begin to see the potential in CSP. The future for concentrated solar power will be brighter once the CSP supply chain is improved and more people are interested in it.

Research is ongoing to determine how CSP could be used to make fuel from light and air. According to the IEA by the end century, carbon dioxide will have to be eliminated in order for global temperatures to stay below 2 degrees Celsius. Concentrated solar energy is expected to play a major role in helping remove carbon dioxide.

Researchers from the US Department of Energy’s Oak Ridge National Laboratory are studying how CO2 can captured from the air and extracted using amino acid chemistry.

Climeworks, a direct air capture company, has developed a carbon removal technology. This technology can capture atmospheric carbon using a filter and low-grade heat to provide energy.

Here is a video explaining how this technology works.