What can solar energy be used for?

At present, the direct utilization of solar energy by human beings is still in the primary stage, mainly including solar heat collection, solar hot water system, solar greenhouse and solar power generation. Solar collector solar water heater device usually includes solar collector, water storage tank, pipeline and water pump. In addition, in winter, heat exchangers, expansion water tanks and power generation devices are needed in case the power plant cannot supply power. Solar collector is a device that receives solar radiation and transfers heat to heat transfer working medium in solar thermal system. According to the heat transfer working medium, it can be divided into liquid collector and air collector. According to the way of lighting, it can be divided into two types: concentrating heat collector and absorbing heat collector. There is also a vacuum collector: a good solar collector will take 20 to 30 years. Starting from 1980, the collector should be maintained for 40 ~ 50 years, with little maintenance. The most widely used solar energy in the early days of solar water heating system was to heat water, and now there are millions of solar water heating devices all over the world. The main components of solar hot water system include heat collector, water reservoir and circulating pipeline. In addition, there may be auxiliary energy devices (such as electric heaters, etc. ) When there is no sunshine, there may also be a device for forcibly circulating water to control the water level or the temperature of electrical components and pipes connected to the load. Solar water heating system can be divided into two types according to the circulation mode: 1 and natural circulation mode: this type of water storage tank is placed above the heat collector. Water is heated by solar radiation in the heat collector, and the temperature rises, which leads to different water temperatures in the heat collector and the water storage tank, resulting in density difference and buoyancy. This thermosiphon phenomenon promotes the natural flow of water in the water removal tank and collector. According to the relationship with the density difference, the water flow is directly proportional to the solar energy absorption of the collector. This type has been widely used because it does not need circulating water and its maintenance is very simple. 2. Forced circulation: the water in the hot water system circulates between the heat collector and the water storage tank. When the water temperature at the top of the collector is several degrees higher than that at the bottom of the water storage tank, the control device will start the water to flow. There is a check valve at the water inlet to prevent water from flowing back from the collector at night, resulting in heat loss. The flow rate of this kind of hot water system can be known (because the flow rate from water is known), so it is easy to predict the performance and calculate the heating water quantity in a certain period of time. For example, under the same design conditions, it has the advantage of obtaining higher water temperature than the natural circulation method, but because water must be used, there are problems such as water and electricity, maintenance (such as water leakage, etc.). ) and intermittent control device, easy to damage the water. Therefore, except for large hot water systems or occasions where high water temperature is needed, forced circulation water heaters are usually used. Greenhouse uses solar energy to warm rooms in winter, which has been used in many cold areas for many years. Because the temperature is very low in winter in cold areas, there must be heating equipment indoors. If you want to save a lot of fossil energy consumption, try to use solar radiation heat. Most solar greenhouses use hot water systems, and some also use hot air systems. Solar greenhouse system consists of solar collector, heat storage device, auxiliary energy system and indoor greenhouse fan system. Its process is solar radiation heat conduction, which stores heat energy through the working fluid in the collector and then supplies heat to the room. The auxiliary heat source can be installed in the heat storage device, directly in the room or between the heat storage device and the room. Of course, heat energy can also be directly applied to the design of direct-heating greenhouse without double heat storage, or directly use solar energy for thermoelectric or photoelectric power generation, and then heat the room, or use it as a greenhouse through heating devices in cold and warm rooms. The most commonly used greenhouse system is a solar hot water device, which introduces hot water into a heat storage device (solid, liquid or phase change heat storage system), then drives indoor or outdoor air into this heat storage device through a fan to absorb heat, and then transports this hot air indoors; Or another liquid flows into the heat storage device to absorb heat. When the hot fluid flows into the room, the heated air is blown into the room by the fan, thus achieving the effect of warming the room. Solar power generation directly converts solar energy into electric energy, and stores the electric energy in a capacitor for use when needed. Solar off-grid power generation system The solar off-grid power generation system includes 1 and solar controller (photovoltaic controller and wind-solar complementary controller) to adjust and control the generated electric energy. On the one hand, the adjusted energy is sent to DC load or AC load, on the other hand, the excess energy is sent to storage battery for storage. When the generated electric power can't meet the load, the solar controller transmits the electric energy of the storage battery to the load. After the battery is fully charged, the controller should control the battery not to be overcharged. When the electric energy stored in the battery is released, the solar controller should control the battery not to be over-discharged to protect the battery. When the performance of the controller is not good, it will greatly affect 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 to ensure that the load uses electricity at night or in rainy days. 3. Solar inverter is responsible for converting DC into AC for AC load. Solar inverter is the core component of photovoltaic wind power generation system. Due to the relatively backward, remote and difficult maintenance areas, in order to improve the overall performance of photovoltaic wind power generation system and ensure the long-term stable operation of the power station, high requirements are put forward for the reliability of the inverter. In addition, due to the high cost of new energy generation, the efficient operation of solar inverter is also very important. The main products of solar off-grid power generation system are classified as A, photovoltaic module B, fan C, controller D, battery E, inverter F, wind/photovoltaic power generation control and inverter integrated power supply. 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 power grid through grid-connected inverters without battery energy storage. Because the electric energy is directly input into the power grid, there is no need to configure the battery, which saves the process of energy storage and discharge of the battery, can make full use of the electric energy generated by renewable energy, reduce energy loss and reduce system cost. Grid-connected power generation system can use commercial power and renewable energy in parallel as the power supply of local AC load, reducing the power shortage rate of the whole system. At the same time, renewable energy grid-connected system can play a role in peak regulation of public power grid. Grid-connected power generation system is the development direction of solar wind power generation and represents the most attractive energy utilization technology in 2 1 century. The main products of solar grid-connected power generation system are classified as A, photovoltaic grid-connected inverter B, small wind turbine grid-connected inverter C and large fan converter (double-fed converter, full-power converter).

[Edit this paragraph] Space solar power supply

The first space solar cell was mounted on Vangtuard I launched in 1958, and it adopted a bulk structure with monocrystalline silicon substrate, with an efficiency of about 10%(28℃). 1970s, people improved the battery structure, adopted BSF, lithography and better anti-reflection film, so that the efficiency of the battery was improved to 14%. In 1970s and 1980s, the global production of terrestrial solar cells doubled every 5.5 years. However, the performance of space solar cells in space environment, such as radiation resistance, has been greatly improved. Due to the rapid development of solar cell theory in 1980s, the performance of solar cells on the ground and in space has been greatly improved. In 1990s, the research and development of thin-film batteries and ⅲ-ⅴ family batteries developed rapidly, and the structure of concentrating array became more economical, and the market competition of space solar cells was fierce. There are two main ways to continue to study higher performance solar cells: concentrating cells and multi-band gap cells. × Main performance of space solar cells Battery efficiency Because the efficiency of solar cells is generally different under different light intensity or spectral conditions, space solar cells generally adopt AM0 spectrum (1.367KW/㎡/m2), and the battery efficiency is generally tested by AM 1.5 spectrum (that is, the ground is sunny at noon,1.000 KWM-). The spectral efficiency of solar cells in AM0 is generally 2 ~ 4 percentage points lower than that of AM 1.5, for example, the efficiency of a Si solar cell with AM 1.5% is about 19%). ◎ 25℃, Efficiency of solar cell under AM0 condition Cell type area (cm2) Efficiency (%) Cell structure Ordinary silicon solar cell 64cm2 14.6 Single junction solar cell Advanced silicon solar cell 4cm2 20.8 Single junction solar cell GaAs solar cell 4cm2 1 .8 Single junction solar cell InP solar cell 4cm21 9.9 single-junction solar cell GaInP/GaAs 4cm2 26.9 monolithic stacked double-junction solar cell GaInP/GaAs/Ge 4cm2 25.5 monolithic stacked double Ge 4cm2 27.0 monolithic stacked triple-junction solar cell ◎ concentrating cell GaAs solar cell 0.07 24.6 100 x gainp/ GaAs 0.25 26.4 50x, monolithic stacked double-junction solar cells GaAs/GaSb 0.05 30.5 100X, mechanically stacked solar cells Space solar cells work outside the atmosphere, and the average solar irradiation intensity in low-earth orbit is basically unchanged, which is usually called AM0 irradiation, and its spectral distribution is close to that. Therefore, most space solar cells are designed and tested by AM0 spectrum. Space solar cells usually have high efficiency, so specific power output can be obtained under the condition of limited space emission weight and volume. Especially in some specific launch missions, such as microsatellites (weight 50 ~ 100 kg), the specific power per unit area or weight is required to be higher. Radiation resistance When space solar cells work outside the earth's atmosphere, they will inevitably be irradiated by high-energy charged particles, which will lead to the attenuation of battery performance. The main reason is that electron or proton radiation reduces the diffusion length of minority carriers. The degree of photoelectric parameter attenuation depends on the material and structure of solar cells. There are also reverse bias, low temperature, thermal effect and other factors, which are also important reasons for battery performance attenuation. Especially for laminated solar cells, the battery performance degradation may be more serious because of the significant difference in thermal expansion coefficient. Reliability of space solar cells The reliability of photovoltaic power supply plays a key role in the success of the whole launch mission. Compared with ground applications, the cost of solar cells/arrays is not important, because the balance cost of space power supply system is higher and the reliability is the most important. Space solar array must undergo a series of rigorous reliability tests, such as mechanical, thermal and electrical tests. Silicon solar cell Silicon solar cell is the most commonly used satellite power supply. Since 1970' s, due to the development of space technology, the power demand of various aircrafts is increasing. While accelerating the development of other types of batteries, the United States, Japan, ESA and other countries with more developed space technology have successively carried out research on high-efficiency silicon solar cells. Represented by Sharp Corporation of Japan, SUNPOWER Corporation of the United States and ESA, they are in a leading position in the research and development of space solar cells. Among them, the development of back field (BSF), back reflector (BSR) and double-layer antireflection film technology is the first generation of high-efficiency silicon solar cells. The typical efficiency of this battery can reach about 65,438+05%, and many satellites in orbit are currently using this battery. In the mid-1970s, COMSAT Institute proposed a non-reflective textured battery (to further improve battery efficiency). However, the application of this battery is limited: first, the preparation process is complicated, so as to avoid damaging the PN junction; Secondly, such a surface will absorb all wavelengths of light, including those infrared radiation whose photon energy is not enough to generate electron-hole pairs, which will increase the temperature of solar cells, thus offsetting the efficiency improvement effect of using suede; Thirdly, the electrode must be extended along the suede, which increases the difficulty of contact and the cost. In the mid-1980s, in order to solve these problems, some technical means of electronic device manufacturing were introduced into the manufacture of high-efficiency batteries, such as inverted gold pyramid textured surface, laser trench buried gate, selective emitter junction and so on. The adoption of these technologies not only further improves the efficiency of batteries, but also makes the application of batteries possible. Especially after solving the problem of band-pass filter to eliminate the temperature rise effect, the application of this battery has become the protagonist of space power supply. Although many technologies were put forward by some research institutes, they were all developed in some big companies. For example, the photovoltaic research center of the University of New South Wales in Australia has appeared the inverted pyramid suede and selective emission junction. The current technical level of Sharp Corporation of Japan and SUNPOWER Corporation of the United States is world-class, and some technologies have even been transplanted to the mass production of ground solar cells. In order to further reduce the compound influence of the back surface of the battery, the back surface structure is passivated to form a point contact, that is, a local back field. The typical structures of these high-efficiency batteries are PERC, PERL, PERT and PERF[ 1], among which the battery with the former structure has been applied in space. Typical high-efficiency silicon solar cells have a thickness of 100μm, also known as NRS/BSF (typical efficiency is 17%) and NRS/LBSF (typical efficiency is 18%). They are characterized by selective emission structure with inverted pyramid suede on the front, passivation structure on the front and back to reduce surface recombination, and complete back. In practical application, it is also found that although the battery with local back field technology is generally one percentage point higher than NRS/BSF, the anti-irradiation ability of local back field is usually poor. By the mid-1990s, space power supply engineers found that although the initial efficiency of this battery was relatively high, the final efficiency of the battery was about 25% lower than the initial efficiency, which limited the further application of the battery and the cost of space power supply could not be well reduced. In order to change this situation, the research institute led by Sharp put forward the structure of bilateral junction battery, which effectively improved the terminal efficiency of the battery, and was actually applied in HES and HES- 1 satellites. In addition, the researchers also found that satellites have strict requirements on the location of battery arrays. If the solar array is not facing the sun or is not facing the sun well, it will affect the power of the satellite power supply, which also limits the configuration of the satellite system to some extent. For example, the space station is a complex aircraft, and it is difficult for some battery arrays to ensure sufficient solar angle, so efficient batteries are needed to meet the requirements. Although the conventional high-efficiency battery has been partially applied at present, it still cannot meet the needs of large-scale power supply in space system because of its high α absorption coefficient and limited space and weight. The traditional battery structure is still limited to a great extent. In this case, Russia focused on improving the final efficiency of high-efficiency silicon battery in the early stage of research, and put forward the idea of double-sided battery in the research of battery array and achieved success, which really achieved high efficiency, long life and low cost. × Solar street lamp Solar street lamp is a kind of street lamp that uses solar energy as energy. Because it is not affected by power supply, does not need to bury wires in trenches, and does not consume conventional electric energy, it can be installed on site as long as it is sunny, so it is widely concerned by people, and it is called green environmental protection product because it does not pollute the environment. Solar street lamps can be used for lighting urban parks, roads and lawns, and also for areas with low population density, inconvenient transportation, underdeveloped economy and rich solar energy resources, so as to solve the household lighting problems of people in these areas.

[Edit this paragraph] Solar cells

Power generation principle of solar cells Solar cells are devices that respond to light and can convert light energy into electric energy. There are many materials that can produce photovoltaic effect, such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, selenium, indium, copper and so on. Their power generation principles are basically the same. Now take the crystal as an example to describe the photovoltaic power generation process. P-type crystalline silicon can be doped with phosphorus to obtain N-type silicon and form P-N junction. When light strikes the surface of the solar cell, some photons are absorbed by the silicon material; Photon energy is transferred to silicon atoms, which makes electrons migrate and become free electrons to gather on both sides of P-N junction, forming potential difference. When the external circuit is connected, under the action of this voltage, a current will flow through the external circuit, generating a certain output power. The essence of this process is: the process of converting photon energy into electric energy. The sun is the closest star to the earth and the central celestial body of the solar system, and its mass accounts for 99.865% of the total mass of the solar system. The sun is also the only celestial body in the solar system that emits light by itself, bringing light and heat to the earth. If there is no sunshine, the temperature of the ground will soon drop to near absolute zero. Due to the sunlight, the average temperature on the ground will remain at about 65438 04℃, which forms the living conditions for human beings and most living things. Except atomic energy, geothermal energy and volcanic eruption energy, most of the energy on the ground is directly or indirectly related to the sun. The sun is a fiery gas fireball, mainly composed of hydrogen and helium, with a radius of 6.96× 105km (radius of the earth's 109 times), a mass of about 1.99× 1027t (Earth's 330,000 times) and an average density of about the Earth's. The effective temperature on the surface of the sun is 5762K, while the temperature in the inner central area is as high as tens of millions of degrees. The energy of the sun mainly comes from the fusion reaction of hydrogen polymerization into helium. Every second, 6.57×101kg hydrogen gas is polymerized to generate 6.53× 1 1 kg helium gas, which continuously generates 3.90× 1023kW energy. These energies, in the form of electromagnetic waves, travel through space at the speed of 3× 105km/s and radiate in all directions. The earth only received 2.2 billion of the total solar radiation, that is,1.77×1.01.4 kW reached the upper edge of the earth's atmosphere. Due to the attenuation when passing through the atmosphere, about 8.5× 1.0 1.3 kW finally reaches the earth's surface, which is equivalent to the power generation of dozens of worlds. According to the current rate of nuclear energy generated by the sun, the reserves of hydrogen are enough to last 60 billion years, and the internal tissues of the earth are polymerized into helium due to thermonuclear reaction, and its life span is about 5 billion years. Therefore, in this sense, it can be said that the energy of the sun is inexhaustible. The structure and energy transfer mode of the sun are briefly described as follows. The mass of the sun is very large. Under the gravity of the sun itself, solar matter gathers to the core, and the density and temperature of the core center are very high, which makes the nuclear reaction happen. These nuclear reactions are the energy of the sun, which constantly radiates into space and controls the activities of the sun. According to various indirect and direct data, the sun can be divided into nuclear reaction area, radiation zone, convection zone and solar atmosphere from the center to the edge. (1) nuclear reaction area is the core of the sun within a radius of 25% (i.e. 0.25R), which concentrates more than half of the mass of the sun. The temperature here is about 15 million degrees (k), the pressure is about 250 billion atmospheres (1ATM =10/325 pa), and the density is close to 158g/cm3. The energy generated by this part accounts for 99% of the total energy generated by the sun and radiates outward in the form of convection and radiation. When hydrogen polymerizes, it emits gamma rays. When the rays pass through cold regions, they will consume energy, increase the wavelength and become X-rays, ultraviolet rays and visible light. (2) The radiation area outside nuclear reaction area is the radiation area, with the range of 0.25~0.8R, the temperature dropped to 65438 0.3 million degrees, and the density dropped to 0.079g/cm3. The energy generated by the sun's core is transmitted to this area by radiation. (3) Outside the radiation zone, the convection zone is the convection zone (troposphere), the range is 0.8 ~ 1.0r, the temperature drops to 5000K, and the density is 10-8g/cm3. In the convection area, energy mainly propagates through convection. Convection zone and its interior are invisible, and their properties can only be determined by theoretical calculation consistent with observation. (4) The solar atmosphere can be roughly divided into photosphere, chromosphere, corona and other layers, and the physical properties of each layer are obviously different. The lowest layer of the sun's atmosphere is called the photosphere, from which almost all solar energy is emitted. The continuous spectrum of the sun is basically the spectrum of the photosphere, and the absorption lines in the solar spectrum are basically formed in this layer. The thickness of the photosphere is about 500 kilometers. Chromosphere is the middle layer of the sun's atmosphere and the outward extension of the photosphere, which can extend to thousands of kilometers. The outermost layer of the solar atmosphere is called the corona, which is an extremely thin gas shell that can extend to several solar radii. Strictly speaking, the stratification of the above-mentioned solar atmosphere has only formal significance. In fact, there is no obvious boundary between layers, and their temperature and density change with height. It can be seen that the sun is not a blackbody with a certain temperature, but a radiator with many layers of radiation and absorption at different wavelengths. However, when describing the sun, it is usually regarded as a black radiator with a temperature of 6000K and a wavelength of 0.3 ~ 3.0 microns. At present, the recent development of solar energy utilization has gone from crystalline silicon and thin-film solar cells to new fields of solar energy technology such as organic molecular batteries, biomolecular screening and even bioenergy, which are developed in synthetic biology and photosynthetic biotechnology. A few days ago, it was learned from the Shanghai Science and Technology Commission that the researchers of East China Normal University successfully "reconstructed" chloroplasts in the laboratory with nano-materials, and realized photovoltaic power generation at a very low cost. Chloroplast is the place where plants carry out photosynthesis, which can effectively convert the light energy of the sun into chemical energy. Instead of "replicating" a chloroplast in vitro, this research team developed a new type of battery-dye-sensitized solar cell, which is similar in structure to chloroplast and tries to convert light energy into electric energy. With the support of Shanghai Nano Special Fund, after more than three years of experiments and exploration, the photoelectric conversion efficiency of this bionic solar cell has exceeded 10%, which is close to the highest level in the world. Professor Sun Zhuo, the project leader and director of the Engineering Research Center of the Ministry of Education for Optoelectronic Integration and Advanced Equipment of East China Normal University, demonstrated the sandwich structure of a new type of solar cell-hollow glass with nano "sandwich", and the mystery of photoelectric conversion was hidden in this composite film with a thickness of several tens of microns. The formula of nano "sandwich" is very unique: dye acts as a "light catcher" and nano-titanium dioxide is a "photoelectric converter". In order to make the dye "eat" sunlight as much as possible, the researchers also ingeniously sprinkled some "seasonings"-quantum dots made of nano-fluorescent materials, so that sunlight with different wavelengths can match the "appetite" of the light trap. As long as the formula is continuously improved, the photoelectric conversion efficiency of nano-sandwiches can be improved again and again. As the third generation of solar cells, the biggest attraction of dye-sensitized cells lies in cheap raw materials and simple manufacturing process. It is estimated that the cost of dye-sensitized battery is only equivalent to110 of silicon panel. At the same time, the requirements for lighting conditions are not high, and even if the indoor sunshine is not enough, its photoelectric conversion rate will not be greatly affected. Besides, it has many interesting uses. For example, using plastic instead of glass "splint" can make flexible batteries; When it is made into a display, it can generate electricity and emit light at the same time, thus achieving energy self-sufficiency. Solar energy is a clean and sustainable energy source. The development of solar energy technology can reduce the use of fossil fuels in power generation, thus alleviating the problems of air pollution and global warming.