Solar energy is generated by the sun's hydrogen through nuclear fusion and a kind of energy, the sun emits about only one 22 billionth of the energy to reach the earth's atmosphere, to the upper boundary of the earth's atmosphere, is about 1367W per square meter, to reach the photovoltaic module, converted into direct current, according to the current monocrystalline 300W module 18.3% efficiency, is about is 183W, then the middle of this 1184W energy where did it go?
1, absorbed and reflected by the atmosphere
There are thousands of kilometers of atmosphere over the earth, divided into troposphere, stratosphere, mesosphere, thermosphere and exosphere, about 30% of the sun's energy will be reflected into space, about 19% of the energy is absorbed by the clouds and atmosphere, into wind, thunder, rain and electricity, reaching the earth's surface accounted for about 51%. Since most of the Earth's surface is covered by oceans, the energy that can really reach the land surface is only about 10% of the energy that reaches the Earth's range of radiation. Nevertheless, the use of this energy can be equivalent to 35,000 times of the current global energy consumption.
2、Battery components only absorb the visible part of the energy
Knowledge of the spectrum of sunlight: sunlight is a mixture of different wavelengths of light that vary continuously and contains a variety of wavelengths of light: infrared, red, orange, yellow, green, blue, indigo, violet, ultraviolet, etc., which is visible by red, orange, yellow, green, indigo, blue, violet, visible to the human eye. The longer wavelength part is red light, wavelength longer than red light is infrared light, the shorter wavelength part is violet light, wavelength longer than violet light is ultraviolet light, although the wavelength range of the solar spectrum is very wide, from a few angstroms to tens of meters, but the size of the radiation energy according to the distribution of wavelength is not uniform. The largest area of radiation energy in the visible part, accounting for about 48%, the UV spectrum area of radiation energy accounted for about 8%, the infrared spectrum area of radiation energy accounted for about 44%, in the entire visible spectrum, the maximum energy at a wavelength of 0.475μm, solar cells can only absorb part of the energy, converted into electricity, the UV spectrum area can not be transformed into energy, the infrared spectrum area too long long wave can only be converted to heat.
In the solar spectrum, different wavelengths of light have different energies and contain different numbers of photons. Therefore, the number of photons produced by solar cells receiving light irradiation is also different. In general, silicon solar cells do not respond to ultraviolet light with wavelengths less than about 0.35 μm and infrared light with wavelengths greater than about 1.15 μm, and the peak response is in the range of 0.8 to 0.9 μm. Determined by the solar cell manufacturing process and material resistivity, the peak spectral response at lower resistivity is about 0.9 μm. In the spectral response range of solar cells, the longer wavelength region is usually referred to as the long-wave spectral response or red light response, and the shorter wavelength region is referred to as the short-wave spectral response or blue light response. In essence, the long-wave spectral response depends mainly on the lifetime and diffusion length of the oligons in the substrate, and the short-wave spectral response depends mainly on the lifetime of the oligons in the diffusion layer and the front surface compounding speed.
At present, there are two ways to improve the efficiency of the cell, one is to study new cell materials to broaden the range of response spectrum, such as cascade solar cells is to integrate the sub-cells made of semiconductor materials with different spectral response to make full use of the wavelengths of each segment of the solar spectrum, which can improve the utilization rate through multi-junction cell technology. The second is to correct the cell process, such as diamond wire cutting, surface passivation technology, laser processing technology, etc., to improve the solar energy utilization rate.
3, module encapsulation loss
After encapsulation into modules, due to the module area is larger than the total area of the cell, about 2 percentage points of full-area efficiency loss; second, due to the PV glass light transmission absorption loss of 0.5 percentage points; EVA film light transmission absorption loss of 0.5 percentage points; third, the interconnection strip / sink lead strip resistance loss of 1 percentage point. In total, the loss is about 4 percentage points. With the continuous development of module technology, multi-grid modules, double-glass modules without aluminum frame and MWT back-contact modules without main grid are now available, which can reduce the module encapsulation loss to less than 1%.
