What is Concentrated Solar Power (CSP)?
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Concentrated solar power, also referred to as concentrating solar power, is technology that uses special reflectors to concentrate the energy of the sun onto a small area known as a receiver. The receiver collects the heat and stores it as a gas, liquid, or even solid particles. The heat generated can instantaneously be used to drive an electricity-generating steam turbine, or stored to do so later.
Since concentrated solar power harnesses the heat energy of the sun, it is called a solar thermal energy source. This is in contrast to its better-known solar sibling, solar panels, which create energy from the light of the sun, through a process called solar photovoltaics.
While high costs and technical challenges have limited the adoption of this technology, that all seems to be changing amid growing interest. The Department of Energy is working to improve and promote the CSP’s as a viable source of renewable energy, while private CSP ventures backed by the likes of Bill Gates have recently achieved some success.
Read on to learn more about this promising solar technology.
All types of concentrated solar power operate in the same principle - using concentrated solar thermal energy to produce electricity. The two most common applications of the technology are parabolic trough systems and solar power towers.
Morocco’s Ouarzazate solar complex has 537,600 parabolic mirrors mounted on 19,200 solar collectors. Image source: HeidelbergCement
Parabolic trough CSP systems are a type of linear concentrator system. They get their name from the large, parabolically-curved, trough-shaped collectors that are used to concentrate sunlight onto a linear receiver tube.
The linear receiver tube is filled with a heat transfer fluid that absorbs thermal energy (heat) from the focussed sunlight. The collected heat can then be used immediately to run an electricity-producing heat engine, or be stored to generate power later.
Among the many different types of CSP, parabolic trough systems are considered the most cost-effective at the utility scale. There are already over 100 plants around the world, with the largest being the 580-megawatt (MW) Noor Ouarzazate Solar Complex in Morocco, pictured above.
Power tower: Thousands of mirrors reflect light onto the shiny section on the top of the towers, which is called the central receiver. Image source: HelioSCSP
In power tower solar plants, a tall central tower is surrounded by thousands or even tens of thousands of special flat reflectors known as heliostats. The heliostats adjust their position with the movement of the sun in order to focus solar radiation towards a central focal point, which is known as the receiver.
The receiver collects the thermal energy in a storage medium - which is usually molten salt or water - and the heat from which drives a turbine to produce electricity.
Because of their unique design and components, power towers are known by several different names, including solar towers, molten salt towers, or receiver power plants.
Projects that use salt receivers usually offer thermal storage, which means that the collected heat energy can be stored for several hours before powering the turbine.
The most famous power system is the Ivanpah project located in the Mojave Desert in California. Ivanpah uses 173,500 heliostats and water as the heat-absorbing material. When it opened in 2014, it was the world’s largest CSP plant, with an electricity generation capacity of 392 MW. Meanwhile, the world’s largest CSP plant with storage capacity is the 280MW Solana Solana Generating Station in Arizona.
As of 2020, there were 10 such plants, but there are several projects currently under construction globally. The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) believes this technology will eventually become cheaper than fossil fuel plants.
Here are some other, less commonly used, types of CSP tech:
Like parabolic trough systems, these are also a type of linear concentrator CSP system. They operate in much the same way - long rows of collectors concentrate sunlight into an absorber (receiver) tube. With linear reflectors, however, the mirrors are placed in a wave shape on the ground, and focus their light up to a downward-facing tube.
Left: Linear Fresnel Reflector system; Right: Parabolic Dish system. Images from: Office of Energy Efficiency & Renewable Energy
With a parabolic dish system, a dish-shaped collector is attached to a two-in-one receiver and electricity-producing heat engine. As each individual dish produces electricity, parabolic dishes can be used in a modular fashion, unlike other types of CSP which typically only work as part of a larger power plant.
In November 2019, a secretive company named Heliogen made a big announcement. The company - which is backed by billionaire Microsoft founder Bill Gates — had used Concentrating Solar Power to achieve record-high temperatures of over 1,800 degrees fahrenheit.
The breakthrough was achieved by applying Artificial Intelligence (AI) to the traditional CSP power tower concept. The AI is used to optimize the movements of the solar mirrors, which in turn provide increased amounts of heat-generating magnified (aka concentrated) sunlight.
The extreme heat it generates is ideal for industries that rely on such heat — like cement manufacturing — that are responsible for a high share of global carbon emissions.
In March 2021, Heliogen announced the first commercial deployment of its technology: to power a large Rio Tinto mine in the Mojave desert of California.
Heliogen’s facility in Lancaster, California. Image source: WRAL TechWire
The average cost of concentrating solar power is $0.182, or 18.2 cents per kilowatt hour as of 2019, the most recent year for which complete cost data is available.
We are referring here to the average levelized cost of energy (LCOE) for utility-scale power generation; in simple terms, the average cost for power plants to produce each unit of electricity.
CSP’s 2019 cost (LCOE of 18.2 cents) is 47% lower than its cost in 2010, when its LCOE was 34.6 cents - an impressive reduction in price over the decade.
That said, the energy source remains more expensive than other renewable energy sources like hydroelectric power, solar PV, and wind energy.
The DOE’s Sunshot Initiative, which backs emerging clean energy technologies, is more interested in the cost of CSP with thermal energy storage. According to them, the cost of baseload CSP energy (i.e. CSP that includes storage of 12+ hours) was 10.3 cents per kilowatt hour in 2017. The Sunshot Initiative hopes to see CSP’s baseload cost fall to just 5 cents per kilowatt hour by 2030.
Here is a table summarizing the pros and cons of Concentrated Solar Power, followed by a brief explanation of each:
|Clean and renewable energy source||More expensive than solar PV and wind power|
|Can double as a short-term energy storage system||Only feasible at the utility scale|
|Can compensate for intermittency of other renewables through timeshifting||Concerns over environmental impacts|
|Can generate heat for industrial applications|
No, CSP is not feasible for home energy use.
Current applications of CSP are at the utility scale - large power plants that cost millions (or billions) of dollars to build and that can power thousands of homes. Furthermore, CSP technologies are considered an expensive option when compared to solar power systems that use photovoltaic solar panels, or even fossil fuel generation.
If you want renewable energy for your home, your best option is to consider rooftop solar panels. They are a solution that has seen widespread adoption: there are already over 2 million residential solar installations in the country. Better yet, thanks to generous solar incentives and price drops over the last decade, solar systems now offer quick payback periods of between four and eight years in many states.
Find out if solar panels are worth it for you by getting a solar estimate using our calculator below.