Overview of solar thermal power generation

Solar thermal power generation is a technical form that uses solar concentrators to convert the solar radiation energy into heat energy, and then into electric energy in various ways.

Solar thermal power generation includes concentrated solar thermal power generation (CSP), solar semiconductor thermoelectric power generation, solar chimney power generation, solar pool power generation, solar thermoacoustic power generation, etc.

Concentrated solar thermal power (CSP) is a technology that has been commercialized and applied on a large scale.

CSP is a technical form of power generation through the “light heat work” conversion process, which is similar in principle to the traditional fossil fuel power station. The biggest difference between the two is that the input energy is different. Solar thermal power generation uses solar energy: the concentrator converts low-density solar energy into high-density energy, converts solar energy into heat energy through the heat transfer medium, and does work through the thermal cycle to realize the conversion to electric energy.

Basic principle of solar thermal power generation

The principle of solar photothermal power generation is that the sunlight is gathered to the solar energy collection device through the reflector, and the principle of solar photothermal power generation is that the sunlight is gathered to the solar energy collection device through the reflector, the heat transfer medium (liquid or gas) in the collection device is heated by the solar energy, and then the water is heated to form steam to drive or directly drive the generator to generate electricity. There are three types of solar thermal power generation systems: trough type, tower type and dish type.

Trough type

1. Point focusing technology: the heliostat automatically tracks the sun, and the focused sun is reflected into the heat absorber at the top of the tower. The heat transfer medium in the heating tube of the heat receiver converts the solar energy into heat energy, and then generates electricity through the thermal cycle.

2. The condensing ratio is 300-1000. The overall efficiency of the system is high.

3. Type of heat absorber: water / steam, molten salt, air and other power stations at the initial stage of commercialization often use water / steam as the working medium (mainly considering that the technical risk is small and the structure is relatively simple)

4. The working temperature range of heat transfer medium is 250~1200c, and steam turbine or gas turbine can be used.

  Basic principle of solar thermal power generation

Tower type

1. Line focusing technology: the parabolic trough reflector is used to gather the sunlight on the heat absorption tube located at the focal line, heat the heat transfer working medium (oil or water) in the tube, and then generate steam through the heat exchanger to drive the steam turbine generator unit to generate electricity.

2. The condensing ratio is between 70-80; Low overall efficiency of the system

3. Working medium in the heat absorber: synthetic oil, water, etc. the current working temperature of the medium is generally within 400C.

4. The 354mwsegs power station in the United States was built in the 1980s and has been in operation for more than 20 years.

  Basic principle of solar thermal power generation

dish

1. Point focusing technology: by using a rotating paraboloid reflector, the incident sunlight is gathered at the focal point of the mirror, where a solar energy absorber can be placed to absorb the heat energy and heat the working medium to drive the steam turbine generator unit for power generation, or a solar Stirling power generation device or a high ratio concentrating photovoltaic system (CPV) can be placed to directly generate power.

2. Condensing ratio 1000-3000; High system efficiency

3. The scale of single machine is small, which is very suitable for distributed generation. In January this year, the world’s first commercial dish Stirling system was put into operation in the United States, with a total capacity of 1.5MW and composed of 60 single 25kW systems.

4. As of october2010, California has approved a total of 1372.5mw dish Stirling power plant project.

Characteristics of solar thermal power generation

There are two ways to use solar energy: one is to convert solar radiation into electric energy through photovoltaic cells. The common way to use solar energy is solar cells; Another way is to convert solar radiation into heat energy through solar collectors. The simplest one is the roof water heater used at home.

At present, solar thermal power generation has become a key field of global venture capital. Its principle is to gather the sun’s rays in a pipe or container containing a certain liquid through a condensing device. With the help of solar heat energy, the liquid is heated to a certain temperature to produce steam, which then drives the turbine to generate electricity. The heat energy is converted into electricity. This kind of power generation is called solar thermal power generation.

Since solar thermal power generation requires sufficient direct solar radiation to maintain a certain power generation capacity, the desert is the most ideal site for plant construction. Compared with traditional power plants, solar thermal power plants have two major advantages: the whole power generation process is clean without any carbon emissions; It uses solar energy without any fuel cost.

Solar thermal power has another feature, that is, the cost of thermal energy storage is much lower than that of battery storage. For example, an ordinary thermos can store as much energy as a laptop battery, but the cost of the battery is obviously much higher. The ability to store solar thermal energy means that solar thermal power plants can overcome the disadvantages of possible interruption of power generation in traditional power plants.

However, the price has become a major obstacle to the promotion of solar thermal power generation. For example, in the southwest of the United States, after considering federal tax incentives, the electricity price of solar thermal power plants is about 13 cents to 17 cents per kilowatt hour. The U.S. Department of energy has set a goal to reduce the price of solar thermal power generation to 7 cents to 10 cents per kilowatt hour by 2015 and to 5 cents to 7 cents per kilowatt hour by 2020, so that solar thermal power generation can compete with traditional power generation methods such as coal power.

Examples of solar thermal power generation

Experimental power station

The first solar thermal power generation experimental power station in Asia – after six years of scientific research and construction, China’s first and Asia’s largest tower solar thermal power station – Badaling solar thermal power generation experimental power station was completed in Yanqing and successfully generated power in August 2012. This also makes China the fourth country in the world to master solar thermal power generation technology after the United States, Spain and Israel.

As a key project of the national “863” plan, the whole project research and development started at the end of 2006, and the construction of the experimental power station was broken in July, 2009. Since there is no precedent in China, there are no technical parameters and design specifications at the beginning of the project. The design of heliostat has gone through four generations of research before it is finalized.

The experimental power station is located in dafutou village, Badaling town. The thermal power generation experimental base covers an area of 208 mu. The base includes a 119 meter high heat collection tower and 100 heliostats with a total area of 10000 square meters. After the formal completion of the collector tower, the heat absorber originally placed on the steel tower was successfully installed on the top of the collector tower and officially put into use.

In june2013, the power generation of the power station can be connected to the State Grid. In the second half of the year, the power station will also start to build a 1MW trough thermal power generation system. After it is put into use, the power generation will be further increased.

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