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Solar energy is clean and environmentally friendly, has no pollution, has high utilization value, and the statement that solar energy has no energy shortage. Its various advantages determine its irreplaceable position in energy replacement. Since ancient times, mankind has invented many methods of using solar energy. With the advancement of society and the development of science and technology, solar energy has begun to serve the life and production of modern society. In addition to early products such as solar water heaters and solar stoves, solar cells and solar power stations have come out one after another. Solar powered artificial satellites, solar cars, solar yachts, solar airplanes, solar phones, solar color TVs, solar radios, solar calculators, etc. Products are also constantly emerging.
At present, the direct use of solar energy by mankind is still in its infancy, mainly in the following ways.
1. Solar collector
A solar collector is a device that receives solar radiation and transfers heat to a heat transfer medium in a solar thermal system. According to different heat transfer working medium, it can be divided into liquid collector and air collector. According to the lighting method, it can be divided into two types: concentrating collector and endothermic collector. There is also a vacuum collector. A good solar collector should last 20 to 30 years. Collectors made since 1980 can last 40-50 years and rarely undergo maintenance.
Solar water heater devices usually include solar collectors, water storage tanks, pipes, and other components of pumps. In addition, in winter, heat exchangers, expansion tanks, and power generation devices are needed to prepare for the power plant cannot supply electricity. Solar water heaters first convert sunlight energy into heat energy, and then obtain hot water through natural circulation of cold and hot water. In the early 1970s, the global oil price increase was a blind "catalyst" for the development of solar water heaters. The United States and Japan each sold hundreds of millions of dollars worth of solar water heaters. Many areas in Australia, Greece, and Israel have widely used solar water heaters to supply hot water to homes. There are already more than 20,000 houses in the UK using solar water heaters, and more than 10% of houses in Japan use solar water heaters to supply hot water. More than 100,000 houses in Australia are equipped with solar water heaters.
Many countries are researching and developing new types of solar water heaters. For example, Austria has developed a new type of solar water heater, which is both a water collector and a water reservoir, independent of the direction of the sun. The outer shell of the sphere is made of glass, and inside the sphere is a chromium-nickel steel ball with a fixed capacity of 30 liters. An ordinary serpentine tube is used to feed cold water into the device, which is heated and kept warm by a high vacuum tube (similar to a thermos bottle) between the steel and glass balls. The test results show that under normal sunlight conditions, the device can heat water to 74°C within 6 hours. During the 12-hour night when the simulated ambient temperature is 18°C, the water temperature drops to 40.2°C.
2. Solar water heating system
In the early days, the most extensive solar energy application was used to heat water, and there are millions of solar water heating installations in the world today. The main components of the solar water heating system include three parts: collector, storage device and circulation pipeline. In addition, there may be auxiliary energy devices (such as electric heaters, etc.) for use when there is no sunlight, and there may also be forced circulation of water to control the water level or control the electric part or temperature and the pipeline connected to the load. Wait.
According to different circulation methods, solar water heating systems can be divided into the following two types:
Natural circulation:
This type of storage box is placed above the collector. The water in the collector is heated by solar radiation, and the temperature rises, causing the difference in water temperature in the collector and the water storage tank to produce a density difference, which causes buoyancy. This thermosiphon phenomenon promotes the natural flow of water in the water removal tank and the collector. Due to the density difference, the water flow is directly proportional to the solar energy absorption of the collector. This form has been widely adopted because it does not require circulating water and is easy to maintain.
Forced circulation:
The hot water system uses water to circulate the water between the collector and the storage tank. When the water temperature at the top of the collector is several degrees higher than the water temperature at the bottom of the water storage tank, the control device will start the water to make the water flow. There is a check valve at the water inlet to prevent the water from flowing backward from the collector at night, causing heat loss. The flow rate of this type of hot water system can be known (according to the flow rate of water), the performance is easy to predict, and the amount of heated water within a certain period of time can also be estimated. For example, under the same design conditions, the natural circulation method has the advantage of obtaining higher water temperature, but because it must use water, there are hydroelectric power, maintenance (such as water leakage, etc.), and the control device is always stopped, which can easily damage the water. And other problems exist. Therefore, except for large-scale hot water systems or situations where higher water temperature is required, forced circulation type is selected, and natural circulation type water heaters are generally used.
Japan has also successfully developed a solar thermal storage power generation system. A 1,000-kilowatt solar thermal storage power generation system has been installed in Niuo Town, Kagawa Prefecture, Japan. To heat the steam and superheat it; each of the four steam accumulators is 15 meters high, 2.5 meters in diameter, and has a working pressure of 4.2 MPa.
The working process of the whole system is as follows: the water is heated by the solar collector to become high-temperature steam, and sent to the molten salt heat accumulator to overheat, after being reduced to a certain value, it enters the steam turbine for power generation, and the exhaust steam is condensed and sent Into the air extractor and deaerator, use steam to heat and degas, and then send it back to the collector to complete a thermal cycle.
When the weather is fine and the amount of steam generated by the solar collector is greater than the required amount, the remaining steam is used to heat the molten salt and charge the cylinder to store the heat; in bad weather or at night, the collector produces The amount of steam is less than the required amount. At this time, the heat accumulator emits heat, and together with the steam from the heat collector, it enters the molten salt for heating and drives the steam turbine to generate electricity. By installing a heat accumulator, the fluctuating steam source is changed to stable and continuous steam, which stabilizes the power generation of the steam turbine and satisfies the electricity demand.
The use of solar energy for heating rooms in winter has been used for many years in many cold areas. Because the temperature in the frigid zone is very low in winter, it is necessary to have heating equipment indoors. If you want to save a lot of fossil energy consumption, try to use solar radiant heat. Most solar heating houses use hot water systems, and some also use hot air systems. The solar heating room system is composed of a solar collector, a heat storage device, an auxiliary energy system, and an indoor heating room fan system. The process is solar radiation heat conduction, and the heat energy is stored through the working fluid in the collector and then heated to the room . The auxiliary heat source can be installed in the heat storage device, directly installed in the room, or installed between the storage device and the room, and other different designs. Of course, it is also possible to directly use the heat energy in the heating room design without dual heat storage, or directly use solar energy for thermoelectric or photovoltaic power generation to reheat the room, or heat the room through the heating device of the cooling and heating room use. The most commonly used heating system is a solar hot water device, which passes hot water into a heat storage device (solid, liquid or phase change heat storage system), and then uses a fan to drive indoor or outdoor air to this heat storage device to absorb Heat, and then transfer this hot air to the room; or use another liquid to flow into the heat storage device to absorb heat. When the hot fluid flows into the room, the fan is used to blow the heated air into the room to achieve the heating room effect.
4. Solar off-grid power generation system
Solar off-grid power generation system includes:
(1) The solar controller (photovoltaic controller and wind-solar hybrid controller) regulates and controls the generated electric energy. On the one hand, it sends the adjusted energy to the DC load or AC load, and on the other hand, it sends the excess energy to The battery pack is stored. When the generated electricity cannot meet the needs of the load, the solar controller sends the energy of the battery to the load. After the battery is fully charged, the controller must control the battery not to be overcharged. When the electric energy stored in the battery is discharged, the solar controller must control the battery not to be over-discharged to protect the battery. When the performance of the controller is not good, it will have a great impact on the service life of the battery, and ultimately affect the reliability of the system.
(2) The task of the solar battery pack is to store energy, so as to ensure the load power consumption at night or on cloudy and rainy days.
(3) The solar inverter is responsible for converting direct current into alternating current for use by alternating current loads. Solar inverters are the core components of photovoltaic wind power generation systems. Due to the relatively backward, remote and difficult maintenance areas, in order to improve the overall performance of the photovoltaic wind power generation system and ensure the long-term stable operation of the power station, high requirements are placed on the reliability of the inverter. In addition, due to the high cost of new energy generation, the efficient operation of solar inverters is also very important.
The main product categories of solar off-grid power generation systems are A, photovoltaic modules B, wind turbine C controller D, battery pack E, inverter F, wind/photovoltaic power generation control and inverter integrated power supply.
The shortcomings of solar cells are high cost, large area of light collecting plate, difficulty in energy storage, and inability to generate electricity on cloudy and rainy days. Over the years, through a lot of research and trial production, the cost of solar cells has been continuously reduced, the varieties have been continuously renovated, and the output has continued to increase. From 1981 to 1984, the world's solar photovoltaic cell output has tripled, reaching 22,800 kilowatts of power generation capacity in 1984. It is estimated that the world's solar photovoltaic cell capacity will reach 5-10 million kilowatts at the end of this century.
In the world, there were reports about silicon solar cells in 1941. In 1954, a monocrystalline silicon solar cell with an efficiency of 6% was developed. In 1958, the solar cell was used for satellite power supply. Before the 1970s, solar cells were mainly used in space due to their low efficiency and expensive prices. After the 1970s, extensive research on solar cell materials, structure and technology has been made, and great progress has been made in improving efficiency and reducing costs. The scale of ground applications has gradually expanded. However, in terms of large-scale use of solar energy, compared with conventional power generation, The cost is still too high. The world’s first silicon solar cell was born in 1954, and then it was used as a power source for artificial satellites, replacing chemical batteries that could only be used for a few days, making the satellite power source work safely for more than 20 years.
At present, the highest laboratory efficiency level of solar cells in the world is: single crystal silicon battery 24% (4cm²), polycrystalline silicon battery 18.6% (4cm²), InGaP/GaAs double junction battery 30.28% (AM1), amorphous silicon battery 14.5% (Initial), 12.8 (stable), confirmed that the cadmium battery 15.8%, the silicon belt battery 14.6%, and the titanium dioxide organic nano battery 10.96%.
China began research on solar cells in 1958 and has achieved a lot of results in more than 40 years. At present, the highest laboratory efficiency level of solar cells in China is: 20.4% (2cm x 2cm) for monocrystalline silicon cells, 14.5% (2cm x 2cm), 12% (10cm x 10cm) for polycrystalline silicon cells, and 20.1% (1cm x cm) for GaAs cells , GaAs/Ge battery 9.5% (AM0), CulnSe battery 9% (1cm x 1cm), polycrystalline silicon thin film battery 13.6% (1cm x 1cm, inactive silicon substrate), amorphous silicon battery 8.6% (10cmx10cm), 7.9% (20cm) x20cm), 6.2% (30cm x 30cm), titanium dioxide nano-organic battery 10% (1cm x1cm).
5. Renewable energy solar grid-connected power generation system
Renewable energy grid-connected power generation system is a power generation system that directly feeds renewable energy generated by photovoltaic arrays, wind turbines, and fuel cells into the grid through grid-connected inverters without storing energy in batteries.
Because the electrical energy is directly input to the grid, the battery is not required, and the process of energy storage and release of the battery is eliminated. The electricity generated by renewable energy can be fully utilized, energy loss is reduced, and system cost is reduced. The grid-connected power generation system can use city electricity and renewable energy in parallel as the power source of the local AC load, reducing the load shortage rate of the entire system. At the same time, the renewable energy grid-connected system can play a role in peak regulation of the public grid. Grid-connected power generation system is the development direction of solar wind power generation and represents the most attractive energy utilization technology in the 21st century.
The main product categories of solar grid-connected power generation system A, photovoltaic grid-connected inverter B, small wind turbine grid-connected inverter C, large wind turbine converter (double-fed converter, full power converter).
6. Solar water reverse osmosis desalination system
The solar battery-powered reverse osmosis desalination system does not require an external power source, so it has obvious advantages in construction and operation in islands and desert areas. The desalination system is equipped with a battery of a certain capacity, which can eliminate the influence of weather, sunshine and other factors on the reverse osmosis water production during the year. In order to adapt the reverse osmosis system to changes in daily radiation, solar cells can be combined in-line or in parallel, and the desalination system can be combined in single or multiple rows to increase the production capacity of the seawater desalination system.
More than half of the electricity consumption of the reverse osmosis desalination system is used to pump seawater to the reverse osmosis membrane. Therefore, while improving the performance of the reverse osmosis membrane, making the reverse osmosis device compact, and further improving the process flow of the system, the energy recovery device is configured on the reverse osmosis equipment, and it is expected that the current reverse osmosis equipment can be made from seawater. The power consumption of taking 1m³ of fresh water drops from 9~10kWh to 6~7kWh.
7. Solar photocatalysis treatment of the environment
In the early 1980s, people began to study photocatalysis to treat the environment, but the application of ultraviolet light in artificial light sources was the main method. Although the effect was significant, the energy consumption was high and the cost was high. Therefore, researchers outside China proposed to combine solar energy with environmental protection and develop technologies for solar photocatalytic degradation and treatment of environmental pollution. The United States took the lead in conducting experiments. They pumped groundwater heavily polluted by trichloroethylene out of the ground, added TiO2 powder catalyst, and used a trough-type parabolic condenser to condense the sunlight, so that sewage flows through a glass tube set on the focal line for photocatalytic reaction. As a result, the concentration of trichloroethylene in the water dropped from 180ppb to less than 0.6ppb, while the standard for drinking water in the United States was 6pp. This is a typical example of the successful treatment of polluted water by solar photocatalysis in the world. At present, there are many projects that are being carried out to treat the environment by solar photocatalytic degradation, mainly including: photocatalytic removal of harmful substances in the air, degradation of organic pollutants and metal pollutants in wastewater, and advanced treatment of drinking water.
8. Use solar energy for cooling
According to reports, solar refrigeration has become a new air conditioning system. Scientists from the Carlos III University of Madrid and the Spanish Supreme Council for Scientific Research have developed a refrigeration technology that is beneficial to the environment. This technology uses solar cooling, thus reducing the greenhouse effect and will not harm the ozone layer.
A research team designed and manufactured an absorption cooler that uses solar energy for cooling. The machine using the new technology looks the same as the ordinary air conditioner, because the brominated slang heat exchange is also used, so the impact on the environment is minimized.
The research team is led by Marcelo Ischijedo, professor of thermal engineering. Researchers use a new solar cooling technology that is different from the existing refrigeration technology. By improving the cooling mechanism, it can produce cold water at 7 to 18 degrees Celsius when the external temperature reaches 33 to 43 degrees Celsius.
Professor Izquierdo pointed out in the research report that a commercial air compression chiller can produce cold water of 12 to 16 degrees Celsius when the external temperature is 28 to 34 degrees Celsius, while the core temperature of the compressor is 80 to 95 degrees Celsius. . Raquel Lizart, a member of the research team, said: "The machine we are developing can generate enough cold water to provide refrigeration for a 40-square-meter room, and the amount of water used is about 120 liters."
9. Use solar energy to develop biogas energy
A new technology of using solar energy to develop biogas energy was successfully developed in the China Agricultural Golden Sun Agricultural Science Research Center. This scientific and technological achievement enables biogas to be used as usual in winter, which completely solves the high construction cost, large area, and construction of traditional underground biogas digesters. Many problems such as long cycle and no gas production in winter. It can produce gas continuously for about 150 to 180 days with one filling. It is easy to use, clean and hygienic like liquefied gas, and has a life span of up to 20 years.
10. Solar Building
There are three types of solar buildings, namely passive: simple structure, low cost, and natural heat exchange to obtain energy; active: complex structure, high cost, and need electricity as auxiliary energy; "zero energy building": complex structure, The cost is high, and all the energy required by the building is provided by the "solar roof". The development of solar buildings is rapid. In the 1980s, the International Energy Organization (IEA) organized experts from 15 countries to conduct joint research on solar building technology, and developed countries in Europe and the United States built demonstration buildings for comprehensive utilization of solar energy. Tests have shown that the energy-saving rate of solar buildings is about 75%, which has become one of the most promising areas for development. Building energy consumption accounts for 1/3 of the world's total energy consumption, of which air-conditioning and heating energy consumption account for a considerable proportion, which is an important market for solar thermal utilization. The development of solar buildings not only requires architects and solar experts to cooperate closely with each other, but also requires fusion, penetration, and integration in concepts and technologies to form new architectural concepts and designs. At present, solar building integration has become an international requirement not only for high-performance solar components, but also for high-efficiency functional materials and special components, such as thermal insulation materials, light-transmitting materials, energy storage materials, smart windows (color-changing glass), and transparent thermal insulation. Materials, etc., these are the contents of future technology development.
11. Other uses of solar energy
Solar drying: After the 1970s, solar dryers developed rapidly, especially in rural areas, where solar drying experiments were done on many agricultural and sideline products.
Solar cookers: Solar cookers can be divided into two types: hot box type and concentrating type. China is the country that promotes the most solar cookers in the world.
In addition, solar energy is also widely used in communications, transportation, agriculture, disaster prevention, consumption, and electronic products.