Concentrating solar power is a collector solar power generation system. Concentrating solar power uses mirrors or lenses to focus a large area of sunlight into a relatively small light collecting area using optical principles. The light-collecting area on the generator is exposed to sunlight and the temperature rises. The solar energy is converted into heat energy by the principle of photothermal conversion, and the heat energy drives the generator through the heat engine to achieve the purpose of generating electricity.
1. Principle of concentrating solar power
The principle of concentrating solar power is to collect sunlight to the solar collector device through the reflector, use the solar energy to heat the heat transfer medium (liquid or gas) in the collector device, and then add water to form steam to drive or directly drive the generator to generate electricity. The principle of concentrating solar power and thermal power generation is basically the same, and the back-end technical equipment is exactly the same. The biggest difference is that the heat source used for power generation is different. Concentrating solar power uses solar energy to collect heat, and thermal power generation uses coal, natural gas, etc. to obtain heat.
2. Concentrating solar power vs pv power difference comparison
● The working principle is different
PV power converts photons into electrons, then into chemical batteries, and then from direct current to alternating current to power the house and grid. A lot of energy is lost in each link of the process, and this is only on a small scale of home energy storage. If it reaches a utility scale, it is conceivable that more energy is lost. Concentrating solar power generates electricity through the conversion process of "light energy-thermal energy-mechanical energy-electrical energy".
Concentrating solar power uses reflectors, condensers and other concentrators to gather the collected solar radiation heat energy to the heat collection device, and heat the heat transfer medium such as heat transfer oil or molten salt in the heating device. Then, the water is heated to high temperature and high pressure steam through the heat exchange device, and the steam drives the steam turbine to drive the generator to generate electricity.
The heat source used in the front-end of concentrating solar power is the same as that of photovoltaic, and the principle of back-end technical equipment and thermal power generation is basically the same. The advantages of both are combined to achieve the purpose of clean and stable power supply.
● Different application scenarios
In addition to centralized power generation, photovoltaics can also be distributed, such as solar facilities built on the roof of the home, which convert sunlight into electrons, and distribute electricity for home use or distribution to the public grid. Concentrating solar power can only be centralized at present, especially suitable for construction in areas with vast terrain and long sunshine time.
● Different ways of storing energy
PV power is greatly affected by the weather and the power supply is unstable. The traditional way of storing solar energy is to use lithium batteries. Regular energy storage lithium battery companies have high quality requirements for batteries. Lithium batteries are relatively expensive and may have safety issues. Concentrating solar power can store the excess heat energy in the energy storage container and release it at night or on rainy days, ensuring continuous and stable power generation for 24 hours. In contrast, the energy storage cost is low and it is clean and environmentally friendly.
3. The composition of concentrating solar power plant
Large concentrating solar power plant can be divided into four parts: heat collection system, heat transfer system, heat storage system, power generation system.
● Heat collection system: The heat collection system is responsible for absorbing solar radiation energy, heating the heat transfer medium, and providing energy for subsequent power generation. It is the core component of the concentrating solar power system. The heat collection system includes two core components: a concentrating device and a receiver.
The concentrating device is controlled by a central control system to track the position of the sun to collect and reflect (redirect) the maximum amount of sunlight, and concentrate the radiant energy on the receiver. The receiver uses the collected energy to heat the internal medium to achieve energy absorption, storage and transportation.
● Heat transfer system: The heat transfer system is an intermediate link that transfers the heat energy collected by the heat collection system to the subsequent system using the heat transfer medium. The most mainstream working fluid at present is molten salt.
Compared with water and heat transfer oil used in the early days, molten salt can maintain a wider working temperature range in the molten state, allowing the system to absorb and store thermal energy under low pressure conditions. However, since the high temperature molten salt has certain corrosion on the inside of the pipeline and the heat storage tank, the material requirements are relatively high.
● Heat storage system: Through the heat storage tank, the concentrating solar power system can centrally store the medium heated by the collector, and then pump it out to exchange heat with water to generate steam to drive the steam turbine to generate electricity. The cooled working fluid can then flow back to the collector system again for reheating.
The heat energy is stored in the heat storage tank, and it can continue to work for a period of time at night or in the case of insufficient light, thereby breaking the limitation of light time and realizing ultra-long power generation time. At the same time, the energy storage tank also has the ability to adjust the output power, and can adapt to the grid dispatching power generation according to the local electricity load. Compared with photovoltaic power station, concentrating solar power has its own heat storage system.
● Power generation system: The power generation system of concentrating solar power is not much different from traditional power plants. It still obtains high-quality superheated steam by heating water, and drives various steam turbines to generate electricity. Since the heat transfer medium used in concentrating solar power is recycled and generates almost no emissions, the power generation process is undoubtedly more environmentally friendly.
4. Types of concentrating solar power system
Concentrating solar power can be divided into four types: tower type, trough type, dish type and Fresnel type according to the way of collecting heat and energy. In the future, tower type will be the focus of development.
● Tower concentrating solar power system: The point-type focusing heat collection system utilizes a large-scale array of heliostat fields that automatically track the sun to accurately reflect the solar thermal radiation to the collector placed on the top of the tower. The sunlight projected on the collector is absorbed and converted into heat energy and heats the intermediate medium, so that it directly or indirectly generates steam at 540℃～560℃. Part of it is used to generate electricity, and the other part of the heat is stored for use in the morning and evening or when there is no sunlight.
● Trough concentrating solar power system: also known as trough mirror system, it is a line focusing heat collection system. The large-area trough parabolic mirror is used to reflect the solar thermal radiation energy, and the medium in the collector located at the focal line is continuously heated to convert the thermal energy into electrical energy. The trough concentrator is a one-dimensional tracking method of the sun, which belongs to medium and high temperature thermal power generation, and the power generation capacity is unlimited after series and parallel integration.
● Dish concentrating solar power system: also known as parabolic reflector Stirling system, it is a point-type focusing heat collecting system and is the earliest solar thermal power generation system in the world. The heat collection system is composed of many parabolic reflector groups. The receiver is located at the focal point of the paraboloid, collects solar radiation energy, heats the heat transfer medium in the receiver to about 750°C, and drives the Stirling engine to generate electricity.
● Fresnel type concentrating solar power system: The working principle is similar to the trough type concentrating solar power, but a Fresnel structure condenser composed of multiple flat or slightly curved optical mirrors is used to replace the parabolic mirror. A rectangular mirror field consisting of many flat, single-axis rotating mirrors automatically tracks the sun. The sunlight is reflected and concentrated onto secondary mirrors with quadric surfaces and linear collectors, which convert solar energy into heat energy, which in turn is converted into electrical energy.
5. Advantages of concentrating solar power
● The concentrating solar power technology is the only renewable energy power generation technology that can achieve friendly grid connection and effective peak regulation at the same time. It is fully capable of meeting the global power demand and effectively reducing carbon dioxide emissions. And the concentrating solar power technology can be mixed with other renewable energy power generation technologies to generate electricity, and the power generation effect is ideal.
● The localization of concentrating solar power equipment in China can promote the growth of the local GDP of the project, which will become one of the main driving forces for the introduction of global support policies.
● Compared with combined cycle or "secondary investment" technologies, concentrating solar power technology has a cost advantage to meet the growing electricity demand in emerging market-related countries. In addition, when the installed capacity of concentrating solar power increases from the current 5GW to be able to compete with wind power (500GW) or photovoltaic (400GW), the cost advantage will be more obvious.
At present, China's concentrating solar power is still in the stage of demonstration projects. Concentrating solar power has high requirements on the construction environment, which makes concentrating solar power unable to compete with photovoltaic power station in large-scale popularization. But it is undeniable that concentrating solar power will become an important form of energy storage. Concentrating solar power can play a role in synergistic and hybrid complementary power generation with wind power and photovoltaics, ensuring stable power output and increasing the proportion of renewable energy in the power system.