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A Review on Concentrated Solar Power (CSP)
Concentrated solar power (CSP) technology is a process of harvesting of solar radiation energy into thermal energy generally to be used for power generation. A large field of movable mirrors known as Heliostats are used to reflect and concentrate solar radiation onto a central receiver. At the receiver, the concentrated solar radiations are converted to thermal energy and transmitted through a heat transfer fluid (HTF) to the steam generator for power generation. There are several types of concentrators, such as parabolic trough, central tower collector and Fresnel reflectors. In a CSP plant that includes thermal storage, the solar energy is first used to heat the synthetic oil or molten salt which is stored providing thermal energy at high temperature in insulated tanks.
According to the data from International Energy Agency (IEA), CSP generation increased rapidly in recent years, achieving a 15.6 TWh electricity generation in 2019. Moreover, with the sustainable development scenario, CSP technology is expected to generate 183.8 TWh electricity in 2030.
Currently, the Levelised Cost of Electricity (LCOE) of CSP plants remains relatively high compared to large scale PV and wind turbines. Below table shows the world average LCOE of different electricity methods.
In addition to electricity generation, CSP has many other industrial applications, such as:
A multi-institutional project funded by the US Department of Energy, cooperated by Sandia National Laboratory, Georgia Institute of Technology and Arizona State University, has proposed an innovative idea: the use of concentrated solar technology as an energy source for the production of ammonia, also known as Solar-Thermal Ammonia Production (STAP).
This new idea of ammonia production does not require fossil fuels, but uses concentrated solar radiation, which greatly reduces costs and lowers carbon dioxide emissions. This advanced thermochemical looping technology to produce and store nitrogen (N2) from air for the subsequent production of ammonia (NH3) via an advanced two-stage process. This project is currently in the early stages of technological maturity, and the Arizona State University team has now begun to conduct system modeling and analysis the thermodynamic and technical economic to look for the optimal operating conditions or system scale.
A Swiss company is on the way of using advanced CSP technology to produce cement, a technology that can generate a high temperature of 1,500 ℃ to replace industrial heat. This technology has the potential to significantly reduce carbon dioxide emissions during cement production. This solar thermal technology can not only replace fossil fuels to provide heat, but also capture the carbon dioxide produced by the reaction during the calcination process of producing cement.
Morocco’s Ourazazate Noor III CSP Tower
This CSP plant project with the largest single unit capacity in the world, the largest energy infrastructure project implemented in Morocco in recent years, this overseas project that has just been awarded the 2020-2021 National Quality Project Gold Award, carries a number of The world’s most and many firsts in the world, has won many national awards and overseas awards. it is a 150 MW gross CSP solar project using a 250 metres (820 ft) solar power tower with 7 hours energy storage. The model HE54 heliostat has 54 mirrors with a total reflective surface of 178.5 square metres (1,921 sq ft). The solar field has 7,400 of such mirrors.
Qinghai Supcon Solar Delingha 50MW Tower Molten Salt Energy Storage CSP Station
The station is one of the first CSP pilot projects in China, with an installed capacity of 50MW, a 7-hour molten salt energy storage system, and 27,135 heliostats. It has a reflective surface of 542,700 square meters and a designed annual power generation capacity of 146 million kWh, which is equivalent to the annual electricity consumption of more than 80,000 households. This plant can save 46,000 tons of standard coal each year, and reduce carbon dioxide gas emission by 121,000 tons, bringing good economic and social benefits.
The project has a total investment of 1.13 billion yuan, a total area of 2.4 square kilometers, and an annual operating cost of about 15.45 million yuan. The project started construction in March 2017, completed and put into operation in December 2018, achieved full-load operation in April 2019, and was officially handed over to production operation at the end of September 2019.
Engineers from a company in Denmark have developed, designed and optimized an asymmetric solar receiver.
According to calculations, once the technology is successfully applied to commercial CSP stations, it can greatly reduce the manufacturing cost of heat absorbers, especially the cost of tubing (up to about 42%). At the same time, it will also greatly reduce the capital cost, and ultimately effectively improve the overall efficiency of the system and reduce the LCOE of CSP.
Currently, the external receiver in tower CSP using molten salts as the heat transfer fluid is a cylindrical shape, with all of the small pipes making up the cylinder – about 20 meters high – the same length all around.
The study found an overall cost reduction from all partners. EPC costs would be reduced by over 14% and total plant efficiency increased by nearly 3%. The LCOE would be reduced by over 13%, meaning less solar energy will be needed to produce the same amount of electricity; reducing the space requirements for the solar field in a 100 MW plant by about 30%.
The greatest cost reduction in the asymmetric receiver was in materials. Overall receiver costs, in steel support, insulation, tracing and so on would be significantly lower and more pronounced in a smaller tower plant, with its smaller solar field, which has a higher optical quality. These overall receiver costs were reduced by over 13% in the 100 MW case but were reduced by more than 20% in the 50 MW case.
In direct materials costs – of just the tubing itself – an asymmetric receiver in a 100 MW CSP plant would save up to 29%, while a 50 MW CSP plant would see savings of up to 42%.
1.Ceramic particle heat storage system
Researchers are trying to use a tower-type CSP station equipped with a ceramic particle heat storage system to provide sustainable renewable energy for the production and drying process of pasta as much as possible, so as to continuously reduce the carbon emissions generated during the pasta production process.
The system will use tower concentrating technology and will build a reflector system containing about 500 heliostats (reflector area is about 6000 square meters) and a 20MWth ceramic heat storage system (which can output 800kWth of heat 24 hours a day). One-millimeter ceramic particles are flowing through the receiver. The solar energy heats them to temperatures of up to 1,000 degrees Celsius. This heat energy can be used to generate steam for power production or to produce industrial process heat. And then the high-temperature particles can be stored in a large insulated container.
Compared with the molten salt medium commonly used in commercial CSP stations, ceramic particles can withstand higher temperatures, are very low in cost, and do not pose a threat to the environment. More importantly, unlike molten salt, the ceramic particle system does not have the risk of fluid freezing, so no auxiliary heating measures are required.
2. Magnesium Silicate as heat transfer fluid and thermal storage material
The “Next-CSP” (Next-Generation Solar Thermal Power Generation) project supported by the European Union’s “Horizon 2020” Research and Innovation Program was completed on September 31, 2020. The project lasts for 48 months and aims to develop new technologies based on high-temperature particles as heat transfer fluid and heat storage medium to improve the performance and reliability of the concentrated solar thermal power generation system.
The NEXT-CSP project chose olivine, a natural magnesium silicate (one of the most common minerals on earth), to make heat transfer solid particles. Although it is not difficult to obtain raw materials, to make full use of this kind of particles requires some major technological innovations, such as the development of matching solar heat absorber technology and a new high-temperature heat exchanger composed of more than 1,300 steel pipes (Compressed air will flow in the tube to achieve heat exchange), in addition to achieving a more advanced combined cycle. On this basis, NEXT-CSP technology integrates the solar heat absorber, heat storage tank, heat exchanger, gas turbine and cold material tank into the tower concentrating power generation system.
The core of the NEXT-CSP project is to use innovative fluidized refractory particles as the heat transfer and storage medium to increase the operating temperature of the system to 750°C or higher, thereby significantly improving the efficiency of the CSP system. It is expected that the theoretical power generation efficiency of the CSP system using solid fluidized particles as the heat transfer and storage medium will be about 20% higher than that of the most advanced molten salt tower CSP power station. At the same time, the design can also reduce the power generation cost by about 25%, and significantly reduce the cost of storage media.
At present, CSP generation still faces many technical problems, including:
1.The investment cost is high, and the initial construction cost of CSP generation is higher than that of utility scale photovoltaic.
2.It is greatly affected by extreme weather. When the temperature is too low, the condensation of the heat transfer medium will cause damage to the pipeline and heat storage system and affect power generation. Therefore, the selection of the heat transfer medium should be determined according to the regional weather conditions.
3.The cost of operation and maintenance is high. From the perspective of China, the “Monitoring and Evaluation Regulations for Solar Thermal Power Generation Projects” approved by the National Energy Administration (China) proposes that a series of parameters such as the cleanliness of the mirror surface and the temperature of the heat transfer medium must be monitored. Therefore, CSP plant lacks effective cleaning and maintenance services.
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