Photo-thermal power generation technology is a brand-new new energy application technology that is different from photovoltaic power generation. It is a process that converts solar energy into heat and then converts thermal energy into electricity. Using the solar thermal energy collected by condensers and other heat collectors, the heat transfer medium is heated to a high temperature of several hundred degrees, and the heat transfer medium generates high-temperature steam after passing through the heat exchanger, thereby driving the steam turbine to generate electric energy. The heat transfer medium here is mostly heat conducting oil and molten salt. Usually we divide the entire CSP system into four parts: heat collection system, heat transfer system, heat storage and heat exchange system, and power generation system.
Heat collecting system: The heat collecting system includes a light collecting device, a receiver, a tracking mechanism and other components. If the heat collection system is the core of the entire CSP, then the condenser device is the core of the heat collection system. The condenser device is a condenser lens or a heliostat. The reflectivity and focus deviation can all affect the power generation efficiency. At present, the efficiency of condensers produced in China can reach 94%, which is not much different from the efficiency of condensers produced abroad. The heat collection system collects solar energy and converts solar energy into heat energy.
Heat Transfer System: The heat transfer system is mainly the heat energy collected by the transmission heat collection system. Heat energy is transferred to the thermal storage system using a heat transfer medium. Heat transfer media are mostly heat-conducting oils and molten salts. In theory, the molten salt has a higher temperature than the heat transfer oil, and has a greater power generation efficiency and is also safer. Heat transfer systems typically consist of preheaters, steam generators, superheaters, and reheaters. The basic requirements of the heat transfer system are: small loss of the heat transfer pipe, small pump power to transport the heat transfer medium, and low cost of heat transfer. During heat transfer, the shorter the heat transfer pipe, the smaller the heat loss.
Heat storage and heat exchange systems: Individuals believe that CSP technology fully embodies the advantages of contrasting photovoltaic power generation technologies in heat storage and heat exchange systems. It will store solar heat energy. It can generate electricity at night, and it can also adapt to the grid to generate electricity according to the local electricity load. The heat storage device is often composed of a vacuum heat insulator or a heat accumulator covered with a heat insulating material. The requirements for heat storage medium in the thermal storage system are: high density of energy storage, abundant sources and low prices, stable performance, non-corrosiveness, good safety, large heat transfer area, good thermal conductivity of heat exchanger, and heat storage medium Better stickiness. At present, China is studying a variety of new technologies and new materials for heat storage, and some experts have proposed the use of ceramics and other inexpensive solid heat storage in order to achieve the effect of reducing power generation costs.
Power generation system: Generators used in solar thermal power generation systems include steam turbines, gas turbines, low boiling point fluid turbines, and Stirling generators. These power generation devices can be selected based on the temperature level of the turbine inlet heat, heat, steam pressure, and other conditions. For a large-scale CSP system, because its temperature level is basically the same as the thermal power system, a conventional turbine can be selected; when the operating temperature is above 800°C, a gas turbine can be selected; for a low-power or low-temperature solar power system, the low Boiling point steam turbine or Stirling engine. Currently used steam turbines are mostly air-cooled. Although the photo-thermal technology power generation system is similar to a thermal power generation system, it still has certain differences. This requires the turbine to have features such as frequent start-stop, quick start, low-load operation, and high efficiency.
Introduction to the main technologies and representative power plants of solar thermal power generation 1. Main technologies of solar thermal power generationSolar thermal power generation, usually called concentrating solar power generation, obtains thermal energy by concentrating solar radiation, converts thermal energy into high-temperature steam, and steam drives turbines to generate electricity. Solar thermal power generation technology is adopted to avoid the expensive silicon crystal photoelectric conversion process, which can greatly reduce the cost of solar power generation. Moreover, this form of solar energy utilization has an advantage that other forms of solar energy conversion cannot match: solar heated water can be stored in huge containers and can still drive steam turbines for several hours after the sun goes down. Current solar thermal power generation can be divided into trough power generation, tower power generation, and Fresnel power generation according to solar energy collection methods.
According to rough statistics, as of February 2016, among the solar thermal power plants built and under construction in the world, the number of trough-type power plants is the largest, accounting for approximately 80% of the total number of solar thermal power stations built and under construction, and the proportion of tower-type power stations exceeds 11%. %, Fresnel-type power station is the least, accounting for less than 9%.
Due to the high overall efficiency of the tower-type CSP system, it is more suitable for large-scale and large-capacity commercial applications. In the planned and constructed solar thermal power plant project, the proportion of towers has exceeded the trough technology. Judging comprehensively, the future tower-type CSP technology may be the main technical school of CSP.
2. Representative power station(1) Andasol solar thermal power plant in Spain
The Andasol solar thermal power station is located near Guadix, Spain's sunny and rich Andalusia. It is Europe's first commercial running solar trough thermal oil power station, which consists of three 50MW installed projects. Andasol No. 1 power station was built in July 2006 and put into operation on the grid in March 2009; Andasol No. 2 power station was built in February 2007 and completed in mid 2009; No. 3 power station was built in August 2008, 2011 It will be completed and put into operation in September. The Andasol 1&2 power station was developed by ACS Cobra (75%) and the Sun Millennium (25%). After the solar millennium bankruptcy, it was transferred to ACS Cobra. The No. 3 power station developer is a consortium of five German companies Ferrostaal/Solar Millennium/RWE/RheinE./SWM.
The classical significance of the Andasol trough power station is that it is the world's first commercial CSP station equipped with a large-scale molten salt heat storage system. By adding 7.5 hours of heat storage system, the annual power generation hours of the power station are greatly increased, and the capacity factor is greatly increased. It reached 38.8%. Afterwards, the storage capacity of many trough power plants in Spain was set as 7.5 hours as Andasol.
(2) Spain Gemasolar solar thermal power station
Gemasolar solar thermal power station is located in Fuentesde AndalucÃa, near Seville, Spain. It is an iconic power station under Torresol Energy and has an installed capacity of 19.9 MW. It began trial operation in May 2011.
Gemasolar uses innovative molten salt heat transfer technology. The heat storage system can continue to generate electricity for 15 hours without sunlight, helping to avoid power supply fluctuations. The power station can achieve 24 hours of uninterrupted power generation in multiple months of the year, even if Night or lack of sunshine in winter. As the world's first commercial CSP station that combines a tower system with molten salt heat transfer and heat storage media, the operation of Gemasolar has become an important milestone in the development of molten salt type tower CSP technology.
(3) Solana solar thermal power station in the United States
The Solana solar thermal power plant is located near Gila Bend, 70 miles southwest of Phoenix, Arizona, and was built at the end of 2010. It was completed in 2013. It was the largest trough power station in the world at that time, and the first thermal storage in the United States with molten salt. Solar thermal power station.
The power station is built by Spain's AbengoaSolar company, with a total installed capacity of 280MW and an annual power generation capacity of 944 million kWh, which can meet the electricity demand of 70,000 households. The total investment of the power station is as high as 2 billion U.S. dollars, and the U.S. Department of Energy loan guarantees provide 1.45 billion U.S. dollars in financing support. Arizona's largest power company, APS, is the PPA contractor for the project. The contract price is 14 cents/kWh, and the acquisition period is 30 years. The total power sales revenue can reach 4 billion US dollars in 30 years.
(4) Ivanpah Solar Thermal Power Plant
The Ivanpah solar thermal power station is located in the Mojave Desert, California, 64 kilometers southwest of Los Angeles. The project was developed by BrightSource Energy Corporation and was put into production in February 2014. The total planned capacity is 392MW, and the three installed aircraft are 133MW, 133MW and 126MW respectively. The construction of the tower-type power station accounted for about 30% of the installed capacity of the total installed solar thermal power plant at that time, and it is also the largest installed capacity of solar thermal power stations in the world.
The project has a total investment of 2.2 billion U.S. dollars and has received a US$1.6 billion U.S. Department of Energy loan guarantee. Technology giant Google invested US$168 million, and NRG Solar invested US$300 million. This also makes it the largest investment in solar thermal power generation projects in history. Ivanpah Solar Thermal Power Plant signed PPA power purchase agreement with Pacific Gas and Power Company (PGE) and Southern California Edison Power Company (SCE). The No. 1 power station installed 126MW, No. 2 and No. 3 power plants installed 133MW. No. 1 power stations and 3 No.2 power station can be purchased by PGE, and No. 2 power station can be purchased by SCE.
(5) CrescentDunes solar thermal power station
The CrescentDunes solar thermal power station is located in Tonope, Nevada, USA, and has an installed capacity of 110MW. It is the world's first large-scale power station using molten salt tower type solar thermal power generation technology. The power station is developed and operated by SolarReserve, and it will be commissioned in 2015 to meet the electricity demand of 75,000 households.
The commissioning of the project proves that the reliability of tower-type molten salt technology applied to 100MW-class large-scale power plants is a leap-frog step in the development of molten salt tower-type solar thermal power generation technology.
(6) Morocco Noor series solar thermal power station
The Noor solar thermal power plant is located in the southern part of Morocco. It is Morocco's first large-scale commercial solar thermal power project with a total installed capacity of 510MW. The Noor1 trough power station with the first phase of 160MW installed was put into operation in February 2016, and the follow-up Noor2 (200MW, trough) and Noor3 (150MW, tower) power stations are under construction. It will be sufficient to meet the electricity demand of 1 million Moroccan households. The above three solar thermal power stations are equipped with a molten salt heat storage system, in which Noor1 project heat storage duration is 3 hours, Noor2 project heat storage time is 7 hours, Noor3 project heat storage time is 8 hours, to meet the power after the sun sets demand.
At present, conventional renewable energy hydropower, photovoltaic power generation, wind power generation and other power generation technologies all have seasonal, intermittent, and stability problems. The combination of CSP and thermal storage systems or thermal power generation can achieve continuous and stable power generation, with adjustable, easy grid connection, and less environmental impact throughout the entire life cycle. Photothermal heat requires no reactive power compensation and high power quality. Therefore, the pace of development of solar thermal power generation has been rapid over the past decade. In particular, the United States and Spain, both countries with rich solar energy resources, are among the best in the world in both technology and commercialization. The Renewable Energy Policy Network released the 2014 Global Status Report on Renewable Energy and conducted research and analysis on the status quo of the development of CSP. The report shows that by the end of 2013, the global installed capacity of solar thermal power generation has increased by nearly 900,000 kilowatts compared to 2012, an increase of 36%, and total installed capacity of solar thermal power generation has exceeded 3.4 million kilowatts. In ten years, the installed capacity of CSP has increased by nearly 10 times. From the end of 2008 to the end of 2013, the annual average growth rate of installed global installed capacity of CSP has remained at around 50%.
CSP policies mainly include on-grid tariffs, renewable energy quotas, net metering tariffs, fiscal and taxation support policies, and green power prices, among which on-grid tariffs and quotas are most commonly used. The on-grid tariff mechanism (FIT), that is, the government mandated that grid companies purchase renewable energy power generation within the coverage of the grid within a certain period of time in accordance with a certain price. The on-grid price forms usually include fixed electricity prices and floating electricity prices. Spain was the first country to adopt the FIT subsidy mechanism to promote the development of the CSP industry. The PPA is an electricity purchase agreement that defines at what price and rules electricity companies (generally public utilities) purchase renewable energy. As the United States has the second largest installed capacity of solar thermal power plants in the world, most of the solar thermal power stations have signed a long-term electricity purchase agreement (PPA) with the grid company. The construction of the oldest trough-type solar thermal power station SEGS power plant in the United States is a 30-year long-term power purchase agreement signed with the local power grid company. The on-grid tariff is 13 to 14 cents/kWh. The largest installed capacity of power plants in the world, the 392,000-kilowatt U.S. Ivanpah solar thermal power plant and Pacific Gas and Power Company (PG&E) and Southern California Edison Power Company (SCE) signed a 25-year PPA power purchase agreement, No. 1 12.6 The power generated by the 10,000 kilowatt power station and the 3rd 133,000 kilowatt power station can be acquired by PG&E, and the power generated by the 2nd 133,000 kilowatt power station can be acquired by SCE.
(a) SpainAccording to the data released by the Spanish grid operator REE:
In 2013, CSP met 1.8% of the country's total electricity demand. In the first four months of 2014, Spain's CSP met the electricity demand of 1.6% in the country. In May, Spain's CSP met 3.7% of the country's electricity demand. In Spain, the installed capacity of CSP increased by 35 million kilowatts in 2013, representing a growth rate of 18%. By the end of 2013, the total installed capacity reached 230 million kilowatts, ranking first in the world. Spain is also investing in the construction of the world's first Gemasolar CSP station that can achieve continuous 24 hours of continuous power generation, with up to 15 hours of heat storage system. This is unmatched by photovoltaic power generation.
1. Electricity price policy
Spain mainly adopts the FIT subsidy mechanism in terms of its CSP policy. It is mainly divided into two types of electricity prices, which can be selected as follows:
(1) Fixed electricity price: 0.27 EUR/kWh in the previous 25 years, 0.22 EUR/kWh after 25 years (Royal Act No. 661/2007).
(2) Adjustable electricity price: Ordinary electricity price + additional subsidies (maximum not exceeding 0.3673 euros/kWh, minimum not less than 0.2712 euros/kWh (Royal Act No. 661/2007).
(3) The Royal Act No. 661/2009 has revised the above policy. Fixed electricity price: 0.28 EUR/kWh in the first 25 years, 0.23 EUR/kWh after 25 years; Adjustable price: normal price + additional allowance (highest More than 0.36 Euro / kWh, minimum not less than 0.26 Euro / kWh).
(4) In 2012, the electricity price subsidy for new-built solar thermal power stations was cancelled. The auxiliary gas-fired power generation part of the original power stations also cancelled electricity price subsidies, and demanded a 7% energy tax.
2. Policy analysis
Spain was the first country to use the FIT subsidy mechanism to promote the development of the CSP industry. In 2002, the on-grid tariff for CSP was 0.12 EUR/kWh, and in 2007 it increased the quota to about 0.27 EUR/kWh. . Thanks to the implementation of the FIT subsidy policy, the development of CSP projects has become a remarkably profitable renewable energy project in Spain. The financing and deployment of power plants can be realized quickly. In the short term, the installed capacity of CSP power generation in Spain has increased significantly by leaps and bounds. , The total installed capacity has long occupied the world's first. However, in recent years, Spain’s development has obviously been more than enough. Some of the CSP plants that were announced earlier will be forced to suspend. This includes the Andasol4 solar thermal power station with an installed capacity of 50,000 kilowatts, the two 50 kilowatts power station at Bogaris, and four solar thermal power station projects of about 200,000 kilowatts. The reason is that due to the national fiscal payment crisis caused by the FIT subsidy policy, the Spanish government was forced to cancel the electricity price subsidy for newly-built solar thermal power stations in 2012, and the auxiliary gas-fired power generation part of the original power station also canceled the subsidy for electricity price, while adding 7% energy. tax.
The disadvantage of the higher fixed FIT subsidy mechanism is that it is difficult to promote the long-term development of CSP technology and the continuous decline in costs, because if the current technology level can guarantee the project's significant yield, the developer will not promote technological innovation. positive. Therefore, the Spanish FIT subsidy mechanism failed to guide the industry to develop in the direction of lower electricity price costs. At the end of 2012, the Spanish government was forced to terminate the FIT policy mechanism due to the financial crisis. Recently, the Spanish government announced or will adopt a new subsidy mechanism and will retroactively replace the implementation of the previous FIT policy, specifically setting the return rate of the CSP project to be about 7.4%, which is slightly lower than the government’s original proposal of 7.5%. . However, this policy has not yet been finalized.
(b) United StatesThe United States was the first country to build a solar thermal power station. As early as the early 1980s, Luz Corporation developed and tested key components of a trough solar thermal power system. During the eight years between 1983 and 1991, Luz Company established 9 solar thermal power plants in the Mojave desert in California, USA. The total installed capacity reached 358,800 kilowatts, which was incorporated into California Edison Power Grid. It is fully proved that CSP can be commercialized or technically feasible. With the world's largest installed capacity of the thermal power plant Ivanpah power station officially put into operation, as of the end of March 2014, the United States has already installed a total installed capacity of 1.435 million kilowatts of solar thermal power generation, ranking second in the world. Bernard Chabot, a renewable energy consultancy company in the United States, released a new analysis report on renewable energy in California. The report shows that in May 2014, CSP met 0.6% of California's electricity demand.
1. Electricity price policy
The United States is special in terms of its CSP policy. It does not use project bidding methods to develop CSP projects, nor does it have a clear, unified, on-grid tariff incentive as in Spain. Instead, it implements a loan guarantee system through the financing of CSP stations. , Federal Investment Tax Credit (ITC) and Renewable Energy Quota Policy. For example, the U.S. federal energy investment tax credit policy gives a maximum of 30% tax concession to solar power plant construction costs, and makes the plan valid for 8 years and expires at the end of 2016.
2. Policy analysis
So far, the U.S. Department of Energy’s loan guarantee program has supported a total of 5 CSP projects, with a total support quota of US$5.835 billion and total installed capacity of 1.282 million kilowatts. The Solana trough power station and the Ivanpah tower power station received US$1.446 billion and US$1.6 billion in loan guarantees from the US Department of Energy. These loan guarantee programs have set up successful financing cases for large-scale, significant CSP projects. The loan guarantee program can reduce investment risks and enable the project to be completed. It can also speed up the emerging technologies to enter the commercialization process as soon as possible. However, it is very difficult to get support for loan guarantees. Only a few significant points can be supported by loan guarantees. At the same time, the loan guarantee program also has the risk of failing to recover debt. In 2011, the bankruptcy of Solyndra, a photovoltaic innovation company, caused the US Department of Energy’s over US$500 million debt to fail to recover, which led to the forced suspension of the loan guarantee support program for renewable energy projects that year. The 30% ITC policy on investment tax credits is also due to expire in 2016, which will bring uncertainties to the development of the raging US CSP industry.
Compared with foreign countries, although there is no effective incentive policy, China’s CSP market has not yet started and the investment prospects are not clear. However, under the framework of the country’s development of emerging strategic industries, with the implementation of the renewable energy quota system, The large power generation group and several private enterprises have started to deploy. Several dozens of megawatts of commercialized CSP projects have been established in the northwest and southwest regions. At present, China has basically produced major equipment for solar thermal power generation. Some of the components have commercialized production conditions, and the solar thermal power generation industry chain has taken shape. The National Development and Reform Commission, the National Energy Administration and the Ministry of Science and Technology continue to pay attention to and support solar thermal power generation projects. In 2006, the Ministry of Science and Technology promulgated the Outline of the National Medium- and Long-Term Scientific and Technological Development Plan (2006-2020), and the 2007 National Development and Reform Commission’s Medium- and Long-Term Development Plan for Renewable Energy, and the National Energy Administration issued in 2011. In the 12th Five-year Plan of the National Energy Technology, solar thermal power generation is clearly listed as a priority and a priority direction for development. However, the commercialization of domestic solar thermal power generation still lags behind. At present, the total installed capacity of domestic completed and put into operation is only a dozen or more megawatts of districts, and the number of buildings under construction does not reach 100,000 kilowatts. This is far from reaching the 1 million kilowatts required by the “12th Five-Year Plan†for solar thermal power generation. The reasons can be roughly attributed to: (1) Delay in the introduction of electricity pricing policies, and the inability of investment income to advance in real terms; (2) Major central enterprises want to preempt resources before the outbreak of CSP market; (3) Technology for project implementation The difficulty in all aspects is far greater than the initial plan and it is difficult to advance as expected.
In terms of CSP policy, we should seriously reflect on lessons learned from CSP policies such as the United States, Spain, and India. Spain's FIT tariff policy and U.S. energy investment tax credits, loan guarantees, and other policies should be effectively combined, while avoiding India’s set-up. The disordered competition caused by the low ceiling price will be more conducive to promoting the development of the CSP industry. Therefore, do not choose only one of these methods. FIT and loan guarantees are good tools for promoting the development of CSP. Loan guarantee can promote the rapid start of the project early, and FIT can guarantee the project's profitability after it is put into production. However, FIT should be set at a reasonable level. It needs to consider the industry's long-term development goals, meet market expectations, and guide it to a better direction. The loan guarantee policy requires careful evaluation of the risk of the project and avoids the risk that the US Department of Energy cannot recover the debt.
Since the first solar thermal power station US SEGS power station was put into production in the 1980s, the development of CSP has been more than 30 years. The technology still has great room for innovation and optimization, and the LCOE (cost per kWh) also has a significant decline. . As a policy-oriented industry, CSP should be based on the actual situation in China, and formulate a localization policy for CSP, which will undoubtedly play a decisive role in the long-term and orderly development of China's CSP industry.
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