How PV Power Plants Run Safely in Hot Summer
In recent years, due to the greenhouse effect and the Nino phenomenon, high summer weather has generally occurred around the world. Excessive temperature not only leads to a decrease in power generation, but also seriously affects the operating state and service life of photovoltaic modules, causing the insulation performance of motor coil enameled wires of photovoltaic modules, cables, inverters and other electrical equipment to decline, and cable insulation to soften or even melt, resulting in The short circuit of the circuit will cause a fire in the photovoltaic power station, endangering personal safety and property safety.
1、Influence of high temperature on various equipment of photovoltaic power station
01 The effect of high temperature on the performance and power generation of photovoltaic modules
1) As we all know, a photovoltaic cell is a semiconductor device with negative temperature characteristics. The higher the temperature, the worse the power generation performance. At present, the power negative temperature characteristics of most photovoltaic modules on the market are around -0.2~-0.4%/℃, while The rated power of photovoltaic modules is measured under standard conditions of 25°C. When the panel temperature of photovoltaic modules is as high as 75°C, the loss of power generation due to high temperature will reach 10% to 20%.
2) Excessive temperature will not only lead to a decrease in photovoltaic power generation, but also lead to the displacement of the internal cells of the photovoltaic module, which will seriously cause a short circuit of the internal cells or wiring of the module, resulting in module failure. The main packaging material for photovoltaic modules is EVA, a plastic that melts at temperatures above 80°C. Since photovoltaic modules usually have a certain inclination angle during installation, when the temperature of the photovoltaic module panel is too high, the internal EVA melts, and the photovoltaic cells will sag due to gravity. If the module is not fixed properly during the packaging process or the internal fixation fails due to high temperature, internal short circuit, open circuit and other faults will occur due to cell displacement and other reasons, resulting in the module not working properly or damaged.
3) Long-term high temperature will also accelerate the attenuation of photovoltaic cells, which will affect the performance of photovoltaic power generation for a long time. The high operating temperature of the cells will also aggravate various hot spots, resulting in permanent deterioration or damage to the power generation performance of the cells.
02 Influence of high temperature on cable and electrical insulation
High temperature has a direct negative impact on the performance and life of insulating materials. Whether it is enameled wire of coils such as motors, transformers, and inductors, or wires and cables such as various plastic wires, they have limited resistance to high temperature. Excessive working temperature will lead to problems such as the decline of insulation performance, and in serious cases, it will lead to insulation collapse, causing short-circuit explosion or fire.
03 Influence of high temperature on electronic equipment such as inverters
1) The photovoltaic power station has electronic equipment such as inverters, which contain a large number of ordinary electronic components, integrated circuits and high-power switching transistors. Usually, the working temperature range of civil-grade electronic components is -35℃～70℃, and the working temperature of most photovoltaic inverters is -30～60℃. Beyond this operating temperature range, both ordinary electronic circuits and integrated circuits will enter an unstable state. This state will lead to circuit equipment shutdown in light, and serious circuit logic confusion and equipment damage.
2) There will be a large number of electrolytic capacitors in the photovoltaic inverter. At the same time, in order to stabilize the voltage at the photovoltaic input terminal and prevent interference, there are usually large-capacity electrolytic capacitors in varying numbers. These capacitors are very afraid of high temperature, and high temperature will cause capacitors. The internal electrolyte gradually volatilizes, resulting in a decrease in the capacitance of the capacitor or even scrapping.
3) The high-power thyristor in the photovoltaic inverter is also a device that is very sensitive to high temperature. Too high temperature will affect the correct operation and service life of the high-power thyristor, and too high a temperature will cause the high-power thyristor to burn out.
04 The effect of high temperature on photovoltaic connectors
At present, international standard MC4 connectors are widely used for the connection between photovoltaic power generation components and component strings, as well as for the DC terminal connection of combiner boxes, inverters and other components.
The MC4 connector is a single-core connector, which has many advantages such as good sealing, convenient connection, convenient maintenance and maintenance. But it also has defects such as being afraid of high temperature, easy to age, and afraid of rain. During the installation and use of component connectors, avoid exposure to sunlight, high temperature, rain, etc., so as to avoid aging of the connectors, corrosion of internal connectors, and cables, resulting in increased contact resistance, or even ignition, resulting in a drop in system efficiency or a fire accident.
In a small-scale photovoltaic power station, there are usually hundreds or thousands of such connectors. The poor working condition of any one of them will affect the increase of the internal resistance of the DC side, resulting in a decrease in the power generation efficiency of the power station. The poor contact will cause the connector to heat up or even burn the connector, which will lead to the burning of the combiner box and the inverter, and even lead to a large-scale fire.
2、Problems needing attention in operation and maintenance of photovoltaic power station in high temperature season
The DC side of photovoltaic power plants has high voltage, large current, many string connectors, and complex installation environment. Many connectors are exposed to sunlight or exposed to wind and rain, which are prone to poor contact and even fire, burning and other fire hazards. The high temperature in summer will add many uncertain hidden dangers to the photovoltaic power station, and the possibility of electrical failure and fire will increase. For electrical fires, the principle of “prevention first” must be implemented to prevent problems before they occur. Special attention should be paid to the ventilation and heat dissipation of equipment and parts such as photovoltaic modules, inverters, transformers, wires and cables, and joints. Abnormal temperature rise should be handled or shut down in time to avoid major accidents.
Once a fire occurs in the power facilities of a photovoltaic power station, the inverter should be turned off first, the AC power supply should be cut off, and then the photovoltaic module string circuit should be disconnected as soon as possible to ensure the safety of firefighting personnel and control the fire in the later stage. In the event of a fire in a photovoltaic power station, firefighters must wear insulating shoes when entering the above range, and insulating gloves when touching the equipment shell and frame. For 10-35kV high-voltage electrical fires, keep the minimum distance between the fire extinguisher nozzle and the charged body should not be less than 0.4-0.6m. Do not touch the body or the fire extinguisher in your hands with live wires or electrical equipment to prevent electric shocks during firefighting. Electrical fire extinguishers should use dry powder fire extinguishers, carbon dioxide, 1211, carbon tetrachloride fire extinguishers or dry sand, etc. Water and foam fire extinguishers are strictly prohibited.