The calculation method of photovoltaic power generation capacity is as follows:
Theoretical annual power generation = total annual average solar radiation * total battery area * photoelectric conversion efficiency
However, due to various factors, the power generation of photovoltaic power plants is actually not that much.
Actual annual power generation = theoretical annual power generation * actual power generation efficiency
So what are the factors that affect the power generation of photovoltaic power plants, let's take you to understand.
1. The amount of solar radiation
A solar cell module is a device that converts solar energy into electrical energy, and the intensity of light radiation directly affects the amount of electricity generated.
2. The tilt angle of the solar cell module
The data obtained from the weather station is generally the amount of solar radiation on the horizontal plane, which is converted into the amount of radiation on the inclined plane of the photovoltaic array to calculate the power generation of the photovoltaic system. The optimal inclination is related to the latitude of the project location. The approximate experience values are as follows:
A. Latitude 0°～25°, the inclination angle is equal to the latitude
B. Latitude is 26°～40°, and the inclination is equal to latitude plus 5°～10°
C. The latitude is 41°～55°, and the inclination is equal to the latitude plus 10°～15°
3. Conversion efficiency of solar cell modules
Photovoltaic modules are the most important factor affecting power generation. At present, the conversion efficiency of polycrystalline silicon modules of first-line brands on the market is generally above 16%, and the conversion efficiency of monocrystalline silicon is generally above 17%.
4. System Loss
Like all products, during the 25-year life cycle of photovoltaic power plants, the efficiency of components and the performance of electrical components will gradually decrease, and the power generation will decrease year by year. In addition to these natural aging factors, there are also various factors such as the quality of components and inverters, circuit layout, dust, series-parallel loss, and cable loss.
Generally, the power generation of the system decreases by about 5% in three years, and the power generation decreases to 80% after 20 years.
1. Combination loss
Any series connection will cause current loss due to the current difference of the components; parallel connection will cause voltage loss due to the voltage difference of the components; and the combined loss can reach more than 8%.
Therefore, in order to reduce the combined loss, we should pay attention to:
1) The components with the same current should be strictly selected in series before the installation of the power station.
2) The attenuation characteristics of the components are as consistent as possible.
2. Dust cover
Among all the various factors that affect the overall power generation capacity of photovoltaic power plants, dust is the number one killer. The main impacts of dust photovoltaic power plants are:
1) By shading the light reaching the module, it affects the power generation;
2) Affect heat dissipation, thereby affecting conversion efficiency;
3) The dust with acid and alkali is deposited on the surface of the module for a long time, which erodes the board surface and causes the board surface to be rough and uneven, which is conducive to the further accumulation of dust and increases the diffuse reflection of sunlight.
So the components need to be wiped clean from time to time. At present, the cleaning of photovoltaic power plants mainly includes three methods: sprinkler, manual cleaning, and robot.
3. Temperature characteristics
When the temperature rises by 1℃, the crystalline silicon solar cell: the maximum output power decreases by 0.04%, the open circuit voltage decreases by 0.04% (-2mv/℃), and the short circuit current increases by 0.04%. To reduce the effect of temperature on power generation, the modules should be well ventilated.
4. Line and transformer loss
The line loss of the DC and AC circuits of the system should be controlled within 5%. For this reason, a wire with good electrical conductivity should be used in the design, and the wire needs to have a sufficient diameter. During system maintenance, special attention should be paid to whether the connectors and terminals are firm.
5. Inverter efficiency
Because the inverter has power devices such as inductors, transformers and IGBTs, MOSFETs, etc., losses will occur during operation. The general string inverter efficiency is 97-98%, the centralized inverter efficiency is 98%, and the transformer efficiency is 99%.
6. Shadow, snow cover
In a distributed power station, if there are tall buildings around, it will cause shadows to the components, and should be avoided as much as possible in the design. According to the circuit principle, when the components are connected in series, the current is determined by the least block, so if there is a shadow on one block, it will affect the power generation of the components. When there is snow on the components, it will also affect the power generation and must be removed as soon as possible.