According to the way of generation, energy can be divided into primary energy and secondary energy. Primary energy is the energy directly obtained from nature without any change or conversion, such as crude oil, natural gas, biomass energy, hydropower, nuclear fuel, solar energy, geothermal energy, etc. The energy obtained from the processing or conversion of primary energy sources, such as coal gas, coke, gasoline, kerosene, electricity, and hydrogen energy, are all called secondary energy sources.
According to whether it can be reused, energy can be divided into renewable energy and non-renewable energy. For example, water energy is a renewable energy source, and coal and oil are non-renewable energy sources.
According to whether it causes environmental pollution after consumption, energy can be divided into polluting energy and clean energy. For example, coal and petroleum are polluting energy sources, while hydropower, solar energy, electric power, and phoenix energy are clean energy sources.
Classified according to form, characteristics or conversion and utilization levels, energy can be divided into solid fuel, liquid fuel, gas fuel, hydropower, nuclear power, electric power, solar energy, biomass energy, wind energy, ocean energy, geothermal energy, etc.
- Solar energy and its resources
Solar energy refers to the energy obtained through the conversion of light, heat, photoelectricity and photochemistry by using solar radiant energy. It is a one-time energy and rich in content, and it is free to use without transportation, and it is an ideal energy that does not pollute the environment.
According to calculations, the total power of energy emitted by the sun per second is about 3.8 x 1023kw, and its energy can last at least several billion years. One part of 2.2 billionth of the total radiant energy of solar energy reaches the upper boundary of the earth’s atmosphere, about 1.73 x 1014kW; reaching the surface of the earth is about 96.88 x 1012kW.
- Sunlight and solar spectrum
The energy of the sun is radiated into the universe in the form of light radiation, because light is also an electromagnetic wave. In addition to the properties of interference and diffraction, it also has the photoelectric effect and Compton scattering effect. Light can also be regarded as particles, called photons, which can explain the properties of high-energy particles of light.
Our daily visible light is part of the sunlight, and its wavelength range is 390 ~ 770m, the wavelengths less than 390nm are ultraviolet rays, and those greater than 770nm are infrared rays. In addition, X-rays and Y-rays have shorter wavelengths than ultraviolet rays. There are microwaves, shortwaves, and radio waves that have longer wavelengths than infrared.
In theory, the shorter the wavelength, the greater the energy of the photon, which means that light with a shorter wavelength is light with higher energy.
After sunlight enters the atmosphere, due to atmospheric refraction, scattering, and gas absorption, the spectrum that reaches the ground and the spectrum emitted by the sun have undergone a certain change.
When the solar energy reaches the surface of the earth, the radiation energy is mainly distributed in the visible light region and the infrared region. The former accounts for 50% of the total solar radiation, the latter accounts for 43%, and the ultraviolet region only accounts for 7%. The light radiation ability of 480nm wavelength is the highest.
- Intensity, amount and duration of sunshine
(1) Sunshine intensity Sunshine intensity refers to the energy density of sunlight per unit area and unit time. The unit can be expressed in two forms: if it is heat utilization, it is calories/(cm²·min) [cal/(cm²·min)] or kilocalories eight cm²·hour) [kcal/(cm²·h)] ; If it is electric energy utilization, it is milliwatt/cm² (mW/cm²·) or Joule/(cm²·min) [J/(cm²·min)]. The unit of sunshine intensity is converted into 1kW/m²=1.433 cal/(cm²·min).
The sunlight received by the earth is not a constant quantity, but a variable that changes over time, and sometimes it may change constantly due to factors such as weather and geographic location. Therefore, if solar cell modules are used to generate electricity, the output power will also change continuously with the different intensities of sunlight. This discontinuity is also the biggest shortcoming of the power generation of battery modules.
(2) The amount of sunshine Continuously measure according to the intensity of sunshine, and record daily and month by month in the corresponding time period. Based on these data, the average amount of sunshine in different months can be calculated.
The unit of the amount of sunlight is also different due to different utilization methods. When converted into heat energy, it is calories/cm² (cal/cm²), kilocalories/m² (kcal/m²), and joules/m² (J/m²); conversion When it is electric energy, it is kilowatt-hour/m² (kW.h/m²). 1MJ/m² =23.89cal/cm².
Normally the amount of sunshine is calculated by the cumulative day and month, so the day and month units are added to the denominator to expand the calculation range. For example, keal/(m²·d)[kcal/(m²·day)].
(3) Sunshine duration According to the regulations of the World Meteorological Organization (WMO) in 1981, the definition of sunshine duration is to take the direct sunshine intensity of 0 and 12kW/m² as a threshold. In sunny or cloudy weather, when the threshold is exceeded, the amount of sunshine is measured and calculated Provide daily and monthly sunshine hours.