Solar energy generally refers to the radiant energy of sunlight. The nuclear reaction of "hydrogen" into "helium" in the sun constantly releases huge energy and radiates energy into space. This energy is solar energy. This nuclear fusion reaction inside the sun can last for billions to billions of years. The radiation power emitted by the sun into space is 3.8x10.23kw, of which one billion reaches the earth's atmosphere. 30% of the solar energy reaching the earth's atmosphere is reflected by the atmosphere, 23% is absorbed by the atmosphere, and the rest reaches the earth's surface with a power of 8 trillion kilowatts, which means that the energy that the sun shines on the earth every second is equivalent to the heat released by burning 5 million tons of coal. In a broad sense, solar energy is the source of a lot of energy on the earth, such as wind energy, chemical energy, potential energy of water and so on. The narrow sense of solar energy is limited to the direct conversion of solar radiation energy into light, heat, electricity and photochemistry.

Humans have a long history of using solar energy. As early as 2000 years ago, during the Warring States Period, China knew to use a steel four-sided mirror to focus the sunlight and ignite it. Using solar energy to dry agricultural and sideline products. With the development of modern times, the utilization of solar energy is increasingly extensive, including photothermal utilization, photoelectric utilization and photochemical utilization of solar energy. There are two ways to utilize solar energy: passive utilization (photothermal conversion) and photoelectric conversion. Solar power generation is a new way of renewable energy utilization.

Solar cells convert the energy contained in sunlight into electric energy through photoelectric conversion, solar water heaters use the heat of sunlight to heat water, hot water is used to generate electricity, and solar energy is used to desalinate seawater. At present, the use of solar energy is not very popular, and there are still problems of high cost and low conversion efficiency in using solar energy to generate electricity, but solar cells have been used to provide energy for artificial satellites.

Silicon photovoltaic cells mainly absorb the light energy emitted by the sun. Silicon photovoltaic cells are mainly extracted from sand and developed by Bell Laboratories.

According to records, human beings have used solar energy for more than 3000 years. The use of solar energy as an energy source and power has only a history of more than 300 years. It is a recent thing to really regard solar energy as "the supplementary energy urgently needed in the near future" and "the foundation of future energy structure". Since 1970s, solar energy technology has advanced by leaps and bounds, and solar energy utilization has changed with each passing day. The history of modern solar energy utilization can be counted from 16 15 when French engineer Solomon de Cox invented the world's first solar engine. The invention is a machine that uses solar energy to heat air to expand it to do work and pump water. During the period of 16 15 ~ 1900, many solar power generation devices and some other solar devices were developed in the world. Almost all of these power plants collect sunlight by concentrating light, and the engine power is not large. The working medium is mainly water vapor, which is expensive and of little practical value. Most of them are developed and manufactured by solar enthusiasts themselves. During the 20th century 100, the development history of solar energy technology can be roughly divided into seven stages.

Advantages: (1) universality: the sun shines all over the earth, and both land and sea, mountains and islands can be directly developed and utilized without mining and transportation. ?

(2) Harmless: the development and utilization of solar energy will not pollute the environment, and it is one of the cleanest energy sources, which is extremely valuable in today's increasingly serious environmental pollution. ?

(3) Huge: The solar radiation energy reaching the earth's surface every year is equivalent to13 trillion tons of standard coal, which is the largest energy that can be developed in the world today. ?

(4) Long-term: According to the current speed of nuclear energy generated by the sun, the storage of hydrogen is enough to last for several billion years, and the life of the earth is about several billion years. In this sense, it can be said that the energy of the sun is inexhaustible. ?

Disadvantages:?

(1) dispersion: Although the total amount of solar radiation reaching the earth's surface is large, the energy flow density is very low. On average, near the Tropic of Cancer, when the weather is clear in summer, the irradiance of solar radiation is the highest at noon. In the area perpendicular to the direction of sunlight, the average solar energy received is about 1 000 w; If the average day and night of the whole year is only about 200W W, only about half in winter and only about 1/5 on cloudy days, the energy flow density is very low. Therefore, when using solar energy, in order to obtain a certain conversion power, a set of collection and conversion equipment with a considerable area is often needed, and the cost is high. ?

(2) Instability: Due to the limitation of natural conditions such as day and night, season, geographical latitude and altitude, and the influence of random factors such as sunny, cloudy, cloud and rain, the solar irradiance reaching a certain ground is intermittent and extremely unstable, which increases the difficulty of large-scale application of solar energy. In order to make solar energy a sustainable and stable energy source and eventually become an alternative energy source that can compete with conventional energy sources, it is necessary to solve the problem of energy storage, that is, to store the solar radiation energy in sunny days as much as possible for use at night or in rainy days, but at present, energy storage is also one of the weak links in solar energy utilization. ?

(3) Low efficiency and high cost: The current development level of solar energy utilization is feasible in theory and mature in technology. However, some solar energy utilization devices cannot compete with conventional energy sources economically because of their low efficiency and high cost. In the future, the further development of solar energy utilization is mainly restricted by economy. ?