Principles of solar photovoltaic power generation

Add Time：2020/5/7    Views：283

Photovoltaic power generation is a technology that uses the photovoltaic effect of semiconductor interfaces to directly convert light energy into electrical energy. The key element of this technology is the solar cell. After the solar cells are connected in series for protection, a large-area solar cell module can be formed, and then a photovoltaic power generation device can be formed by cooperating with components such as a power controller.

1. Photovoltaic effect

If light shines on the solar cell and the light is absorbed in the interface layer, photons with sufficient energy can excite electrons from the covalent bonds in P-type silicon and N-type silicon, resulting in electron-hole pairs. The electrons and holes near the interface layer will be separated from each other by the electric field effect of space charge before recombination. The electrons move toward the positively charged N region and the holes move toward the negatively charged P region. Through the charge separation of the interface layer, an outwardly measurable voltage will be generated between the P region and the N region. At this time, electrodes can be added on both sides of the silicon chip and connected to a voltmeter. For crystalline silicon solar cells, the typical value of the open circuit voltage is 0.5 ~ 0.6V. The more electron-hole pairs generated in the interface layer by light, the greater the current. The more light energy the interface layer absorbs, the larger the interface layer, that is, the cell area, and the greater the current formed in the solar cell.

2. Principle

The sun illuminates the semiconductor p-n junction to form a new hole-electron pair. Under the action of the p-n junction electric field, holes flow from the n-region to the p-region, and electrons flow from the p-region to the n-region. After the circuit is connected, a current is formed. This is how the photovoltaic cell works.

There are two ways of solar power generation, one is light-heat-electricity conversion, and the other is light-electricity direct conversion.

(1) The light-heat-electricity conversion method uses heat energy generated by solar radiation to generate electricity. Generally, a solar collector converts the absorbed heat energy into working fluid vapor, and then drives the steam turbine to generate electricity. The former process is a light-heat conversion process; the latter process is a heat-electricity conversion process, which is the same as ordinary thermal power generation. The disadvantage of solar thermal power generation is its low efficiency and high cost. It is estimated that its investment is at least higher than that of ordinary thermal power generation. The power station is 5 to 10 times more expensive.

(2) Light-electricity direct conversion method This method uses the photoelectric effect to directly convert solar radiation energy into electrical energy. The basic device of light-electricity conversion is a solar cell. A solar cell is a device that directly converts sunlight energy into electrical energy due to the photovoltaic effect. It is a semiconductor photodiode. When the sun shines on the photodiode, the photodiode will convert the sun's light energy into electrical energy. Current. When many batteries are connected in series or parallel, they can become a square array of solar cells with relatively large output power. Solar cell is a promising new power supply, with three advantages of permanence, cleanliness and flexibility. The long life of solar cells, as long as the sun exists, the solar cells can be used for long-term investment at a time; with thermal power generation, nuclear power generation In contrast, solar cells do not cause environmental pollution.