In general, we think that efficiency of photovoltaic power generation is designed to be 75%-80%, and it should be operated according to this standard during operation. But in reality, it has encountered such a situation: efficiency of today is 95%, but tomorrow is only 55%. And there are many fluctuations in efficiency values in a month. So everyone has doubts about the efficiency of the power station system: Is there something wrong with the monitoring system? Or is there something wrong with the power station? How to improve the efficiency of photovoltaic power generation?
The generated energy of photovoltaic power plant is determined by three factors: system capacity, peak hours and system efficiency. When the location and scale of the power station are determined, the first two factors are basically determined. System efficiency is the main breakthrough to increase power generation. Combining these three factors, improving the power generation efficiency of photovoltaic power plants can start from the following aspects
1. Solar radiation
When the conversion efficiency of the photovoltaic module is constant, the amount of power generated by the photovoltaic system is determined by the intensity of the solar radiation. Under normal circumstances, the utilization efficiency of photovoltaic system for solar radiation is only about 10%. Therefore, solar radiation intensity, spectral characteristics, and climate conditions need to be considered.
2. Tilt angle of photovoltaic module
The azimuth of the PV module is generally selected in the south direction to maximize the power generation per unit capacity of the PV power plant. As long as it is within ±20° of due south, it will not have much influence on the amount of power generation. If possible, it should be 20° to the southwest as far as possible.
3. Photovoltaic module efficiency and quality
Calculation formula: theoretical power generation = annual average total solar radiation * total PV module area * photoelectric conversion efficiency and the effect of photoelectric conversion efficiency on the power generation of the power station is relatively straightforward.
4. Matching loss of photovoltaic modules
Any series connection will result in current loss due to PV module current differences; any parallel connection will result in voltage loss due to PV module voltage difference. The loss may reach more than 8%. In order to reduce the loss of matching loss and increase the power generation of the power station, we must pay attention to the following aspects.: 1. Reduce the matching loss, try to use the PV modules with consistent current; 2. The attenuation of the PV modules should be as consistent as possible; 3. Use isolation diode.
5. Ensure good ventilation of the PV module
Data shows that for every 1 °C rise in temperature, the output power of the crystalline silicon PV module drops by 0.04%. Therefore, it is necessary to avoid the influence of temperature on power generation and maintain good ventilation conditions.
6. The loss caused by dust cannot be underestimated
The panel of the crystalline silicon is tempered glass, and long-term exposure to the air causes organic matter and a large amount of dust to accumulate. Dust blocking reduces PV module output efficiency and directly affects power generation. It can also cause PV module "hot spot" effects that can cause component damage.
7. Shadow and snow
In the site selection process of photovoltaic power plants, it is necessary to pay attention to the shielding of light. Avoid areas that may block light. According to the circuit principle, when the PV modules are connected in series, the current is determined by a PV module with the least current. So if there is a shadow on a PV module, it will affect the power generation of this series of PV modules. Similarly, the snow should be removed in time.
8. Maximum output power tracking (MPPT)
MPPT efficiency is a key factor in determining PV inverter power generation, and its importance far exceeds the efficiency of the PV inverter itself. MPPT efficiency is equal to hardware efficiency multiplied by software efficiency. The hardware efficiency is mainly determined by the accuracy of the current sensor and the accuracy of the sampling circuit. The software efficiency is determined by the sampling frequency. There are many ways to implement MPPT, but no matter which method is used, the power change of the PV modules is measured first, and then the power change is reacted. The key component of this control is the current sensor. Its accuracy and linearity error directly determine the hardware efficiency. The sampling frequency of the software is also determined by the accuracy of the hardware.
9. Reduce line losses
In the photovoltaic system, the cable accounts for a small part, but the influence of the cable on the power generation cannot be ignored. It is recommended that the line loss of the DC and AC circuits of the system be controlled within 5%. The cables in the system must meet the requirements, such as the insulation performance, the heat and flame resistance, the moisture and light resistance, the type of cable core and the size of the cable, etc.
10. The efficiency of the inverter
The PV inverter is the main component and an important component of the photovoltaic system. In order to ensure the normal operation of the power station, it is particularly important to properly configure and select the inverter. In addition to the technical specifications of the entire photovoltaic power generation system and reference to the product manual provided by the manufacturer, the following technical indicators are generally considered: 1. Rated output power 2. Output voltage adjustment performance 3.Efficiency 4. Starting performance.