Concentrated solar power

Concentrated solar power, often called CSP, is a method of capturing solar energy to produce heat.

Unlike standard solar panels that turn light directly into electricity, CSP systems collect solar thermal energy. This heat can be used for various tasks like cooking, desalination, or generating electricity. The process relies on using mirrors or lenses to focus a large area of sunlight onto a much smaller area. This concentrated light is then converted into intense heat. This heat can power a heat engine, such as a steam turbine, or drive a thermochemical reaction.

The mechanism of CSP begins with solar concentrators that use tracking systems. These mirrors or lenses follow the sun's movement across the sky during daylight hours. By concentrating the light, the system creates high temperatures at a specific receiver.

In a parabolic trough system, the light hits a tube filled with a working fluid. This fluid, which might be molten salt, absorbs the heat as it flows through the receiver. The heated fluid is then used as a heat source for a power generation system. This heat typically drives a steam turbine to produce electricity, similar to how fossil fuel stations operate.

There are four main optical types of CSP technology used today. The first is the parabolic trough, which uses long, curved mirrors.

These are classified as linear focus collectors because they focus light along a line. The second type is the concentrating linear Fresnel reflector, which is also a linear focus collector. The third type is the solar power tower, which uses a central receiver.

This is a point focus type because it concentrates light onto a single point. The fourth type is the solar dish, which is also a point focus system. Point focus collectors achieve much higher concentration factors than linear collectors.

The history of concentrating sunlight is filled with both legends and real inventions. A famous legend claims Archimedes used a "burning glass" to repel Roman ships in 213–212 BC.

While historians doubt this story, scientists have tested the idea with mirrors. In 1866, Auguste Mouchout used a parabolic trough to power a solar steam engine. Later, Frank Shuman built a solar thermal energy station in Egypt in 1913. The first modern concentrated solar plant was built by Professor Giovanni Francia in 1968. His plant in Italy used a tower design to produce 1 MW of power with superheated steam.

In the modern era, CSP has seen various stages of growth and technological shifts. The Solar One project in California was a major milestone in the 1980s. It was later converted to Solar Two in 1995, which used a molten salt mixture for storage. This mixture consisted of 60% sodium nitrate and 40% potassium nitrate. While solar photovoltaic (PV) technology grew rapidly due to falling prices, CSP growth has been slower. However, CSP remains highly valuable because it is a dispatchable form of energy. This means it can provide power even when the sun is not shining.

Global capacity numbers show how CSP fits into the wider energy landscape. In 2021, the global installed capacity for all solar was about 1 terawatt. At that time, CSP accounted for less than 1% of that total, standing at only 6.8 GW. By 2023, the total capacity grew to 8.1 GW, including new projects in China and Dubai. The DEWA project in Dubai set a record in 2017 with a price of US$73 per MWh. In the Atacama region of Chile, prices for solar power reached below $50/MWh in 2017 auctions. These numbers show that CSP is becoming more competitive.

CSP is uniquely useful when compared to photovoltaic solar energy. PV systems often struggle with the "duck curve," where power demand peaks at sunset.

This is exactly when PV capacity begins to ramp down. CSP can solve this by using thermal energy storage. It can store heat as sensible heat or latent heat, such as in molten salt. This allows CSP plants to continue supplying electricity during the night. This ability to store energy makes CSP a strong competitor to natural gas and battery-backed PV systems.