The largest solar thermal power plant in the United States is located in California’s Mojave Desert in San Bernardino County. The Ivanpah Solar Power Facility is a 386-megawatt facility built and operated by the U.S. Department of Energy. It uses distributed power towers and large flat mirrors called heliostats, which are forms of concentrated solar thermal power (CSP) technology.
These massive solar therm power plants generate a considerable amount of energy by using heat to turn steam generators, and they operate at very high temperatures. Coal, natural gas, and nuclear power plants also use thermal energy but must burn a fuel source. Despite photovoltaic solar power plants being more popular and widespread, concentrated solar thermal power (CSP) plants have also proven to be a reliable and effective technology for utility-scale solar plants.
However, CSP systems are not very widespread, and further research is needed to advance this technology. Of the 4,116 billion kilowatt-hours (kWh) of electricity generated at utility-scale power plants in the U.S. in 2021, solar thermal power plants generated about 3 billion kilowatt hours. A combination of high costs and technological issues has led to slow deployment, thus CSP projects are relatively rare.
How CSP Technology at Solar Thermal Power Plants Works
CSP technology uses mirrors to focus the sun's heat (solar thermal energy) to rotate steam turbines or engines, generating electricity. Plant operators can also store the energy generated from CSP plants to produce electrical power later. There are several types of CSP energy technologies, including parabolic trough, compact linear fresnel reflector, power tower, and dish-engine.
Like fossil and nuclear power plants, CSP plants commonly use wet-cooling, a process that counts on water to cool the steam turbines. Unfortunately, this is a water-intensive process which is an issue in water-constrained areas. There is another technique called dry cooling, but it uses fans to cool the turbines, and therefore is not as energy efficient.
Some CSP plants are hybrid systems that use fossil fuels, such as natural gas, along with solar energy. However, this does create greenhouse gas emissions. In addition to electricity generation, CSP technology can also be used for desalination and process heat.
Types Of CSP Technologies Used at Solar Thermal Power Plants
Several types of CSP technology are used in the U.S., and they share some common themes. They all use mirrors to focus sunlight onto a central receiver that circulates a fluid. CSP plants operate at high temperatures and use thermal energy to produce power. Let’s examine the various types of CSP plants.
Parabola/Trough
Parabolic trough systems use long, rectangular U-shaped mirrors to focus sunlight onto receiver tubes that run the length of the mirrors. The fluid that flows through the tubes is heated and sent to a heat exchanger to boil water in a steam generator. Depending on the system design, some concentrated solar power (CSP) plants have mirrors that can track the sun.
Typically, the mirrors are aligned in a north-south layout to maximize the concentration of solar energy, allowing them to track the sun as it moves from east to west across the sky and continuously focus sunlight on the tubes. There are several such solar thermal power plants in the U.S., particularly in Arizona, Nevada, and California.
These CSP plants utilize the efficient heat collection capabilities of parabolic trough technology, demonstrating the effectiveness of CSP plants in harnessing solar energy for electricity generation.
Dish CSP Technology
Solar dish systems contain a mirrored dish that is a similar shape to a large satellite dish. Numerous small, flat mirrors direct and concentrate sunlight onto the solar receiver, which absorbs it and transfers it to an engine generator.
The solar dish points directly at the sun and concentrates the energy at a focal point, and the fluid temperature can reach temperatures of 1,380°F or greater. There are no utility-scale solar thermal dish projects in commercial operation in the U.S. However, parabolic dish CSP technology can also be utilized on smaller-scale projects with one small dish.
Power Tower
These power plants contain a solar power tower system with heliostats to concentrate sunlight on a receiver at the top of the tower. Although some CSP plants use water as a heat-transfer fluid, experimentation is being conducted with molten nitrate salt due to its excellent heat transfer and energy storage abilities. This alternative offers excellent heat transfer and energy storage capabilities, allowing solar tower facilities to store heat and produce energy on demand.
The Ivanpah Solar Power Facility, as mentioned earlier, is one of the two operational solar power tower systems in the United States. These systems demonstrate the potential for efficient energy generation and storage in solar power applications.
CSP Energy Storage
CSP plants use solar radiation for power generation, but the heat can also be stored for later use. Several thermal energy storage technologies have been tested and implemented, including the two-tank direct system, single-tank thermocline system, and two-tank indirect system. CSP storage systems have been tested and in use since 1985.
This enables these plants to be a flexible option for generating power when needed most, even if the sun’s energy is unavailable. Therefore, energy storage capabilities allow renewable energy to generate a larger share of the total energy mix while ensuring a sustainable and reliable power supply.
CSP Technology for Desalination Plants
CSP technology is increasingly recognized as a viable solution for desalination, particularly in arid regions where solar energy is abundant, but water scarcity creates significant challenges. CSP plants can provide a sustainable energy source for desalination processes, addressing two critical global issues: the demand for clean energy and a reliable water supply.
The Need for Energy in Desalination
Desalination plants are energy-intensive operations, typically consuming substantial electricity to convert seawater into fresh water. Traditional methods, such as reverse osmosis, require significant energy inputs, often sourced from fossil fuels, which can increase carbon emissions and operational costs. By integrating CSP technology, desalination plants can harness solar energy, drastically reducing their carbon footprint and energy costs.
Benefits of Concentrated Solar Power for Desalination
Sustainable Energy Supply: CSP plants generate electricity by concentrating sunlight, making them an excellent fit for sunny regions that are often water-scarce. This synergy allows CSP plants to power desalination processes while also contributing to the region's overall energy mix.
Energy Storage Capabilities: CSP palnts often incorporate thermal energy storage, allowing them to store heat generated during the day and use it to produce electricity at night or during cloudy periods. This capability ensures a continuous power supply for desalination, which can operate 24/7, thus improving water availability.
Synergistic Solutions: By co-locating CSP plants with desalination facilities, operators can create a symbiotic relationship where excess energy from the CSP plant can directly supply the desalination process, optimizing resource use and enhancing efficiency.
FAQs About CSP Technology & Solar Thermal Power Plants
Let’s look at some of the most common questions regarding this solar technology.
How Do CSP and Photovoltaics Compare?
Solar PV panels use light, not heat, to make electricity. Both CSP and photovoltaics are used in utility-scale power plants, but PV technology is much more widespread and doesn’t require water for cooling. Utility-scale PV plants are also easier to construct than CSP facilities, and they do not require the same high level of solar radiation as CSP.
Thus, utility-scale PV plants are more common, even in states with moderate levels of solar radiation. By contrast, CSP plants are commonly situated in the Southwestern U.S., Spain, Morocco, India, South Africa, Israel, and Australia, due to their excellent solar resources.
However, CSP technology has a couple of distinct advantages. It produces alternating current (AC) power, so no inverter is needed. Likewise, CSP plants are often designed to store heat for generating electricity at a later time. This means that CSP plants can be used to meet peak energy demand because the power is dispatchable.
However, utility-scale energy storage technologies for PV systems that use lithium-ion batteries have advanced considerably in recent years. Yet, these battery energy storage systems (BESS) are commonly relatively small by comparison to the energy storage abilities of CSP plants. As battery technology advances and costs decrease, BESS at PV plants will likely have greater capacities and become more widespread.
What is the Largest CSP Plant in the World?
The Noor Complex Solar Power Plant in Morocco remains one of the largest CSP plants globally, with a capacity of 580 MW, supplying electricity to about 1 million people. This solar thermal power plant uses molten salt for heat storage, generating energy even after sunset. The plant utilizes significant amounts of water for cooling and mirror cleaning, but newer designs aim to reduce this dependency. Diesel is used minimally, mainly as a backup for temperature maintenance of the molten salt system during specific operations.
What are the advantages and challenges of CSP technology?
Thanks to thermal energy storage, CSP technology offers several advantages, including generating electricity even when the sun is not shining. This makes CSP a reliable and dispatchable renewable energy source. Also, CSP technology can achieve high thermal efficiencies and can be integrated with industrial processes requiring high-temperature heat.
However, CSP technology also faces challenges. The initial capital costs for CSP plants are high, and they require significant amounts of land and water, which can be limiting factors. Therefore, CSP systems are generally best suited to areas with high direct sunlight, limiting their geographic applicability. Technological advancements and economies of scale are essential for reducing costs and expanding the deployment of CSP technology.
Concentrating Solar Thermal Power Could Change Power Plants Forever
Although technological and cost issues are holding back more widespread use of CSP plants, the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories are conducting extensive CSP research to help overcome challenges and develop next-generation approaches. Yet, the rapid decrease in the price of photovoltaics (PV) has made CSP less cost-competitive by comparison. Addressing cost issues will be essential for CSP plants to become more widespread and practical.
One big advantage of CSP technology is its ability to store heat to generate clean energy when power demand is highest. This enables CSP to compete with other dispatchable energy sources, like natural gas.
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