The basic electrical parameters of photovoltaic modules mainly include output power, current, voltage, fill factor and temperature coefficient. The main body of the photovoltaic power station is the photovoltaic module, so the technical parameters of the photovoltaic module are the basic data for the design of the photovoltaic power station. Through the electrical parameters of the components, according to the selected inverter, the number of series and parallel of the components can be selected. The dimensions, weight and structure of the modules are also important technical parameters. They are necessary parameters for selecting suitable brackets, installation methods, and estimating site area. They cannot be ignored in the design of photovoltaic power plants.
Among them, STC (Standard Testing Condition) refers to the standard test conditions of ground photovoltaic modules: air quality AM1.5, solar radiation intensity 1000W/m², temperature 25℃. Briefly describe the key technical parameters.
①Pmax (maximum power) represents the peak wattage, that is, the power value under standard test conditions. The power corresponding to the point where the product of voltage and current on the I-V curve is the largest is the maximum power, and the voltage and current at this time are called respectively. Maximum power point voltage Vmpp and maximum power point current Impp.
②VOC (open circuit voltage) When the external circuit of the component is open, the current flowing through the battery is 0, and the effective maximum voltage of the component at this time is the open circuit voltage VOC
③ When the ISC (short-circuit current) component is short-circuited, the output voltage is 0V, and the current flowing through the battery is the short-circuit current ISC. ISC reflects the ability of the cell to collect photogenerated carriers, which is proportional to the light intensity.
④ηm (module efficiency) is the ratio of the maximum output power of the module to the solar energy received by the module under standard test conditions. Efficiency is an important parameter for comparing components with each other and is determined by the following formula:
ηm=[(maximum output power)/(module area×irradiance intensity)]×100%
In the formula, the maximum output power is Pmax, and the component area refers to the maximum area of the component. If there is a frame, the frame needs to be included.
⑤NOCT (Nominal Operating Cell Temperature) is the nominal operating temperature of the solar cell, which refers to the conditions under which the module installation angle is (45±5)°C, the solar irradiance is 800W/m², the ambient temperature is 20°C, and the wind speed is 1m/s , the temperature of the battery after the module runs steadily under no-load operation. At present, the latest standard is NMOT (Norminal Operating Temperature), that is, the nominal operating temperature of the module: the installation angle of the module is (37±5)°C, the solar irradiance is 800W/m², the ambient temperature is 20°C, and the wind speed is 1m/s. , the battery temperature after the module has stabilized around the maximum power point.
⑥Temperature coefficient (Temperature Coefficient) The temperature coefficient characterizes the relative change of each performance of the component when the temperature changes by 1°C. The temperature coefficients of power, current and voltage are different. The voltage changes with temperature relatively large, and the current changes relatively small with temperature.
⑦Max System Voltage (Max System Voltage) refers to the sum of the open circuit voltages after the components are connected in series in the system, and each material of the components needs to be able to withstand this voltage value.
Figure 1 shows the I-V curves of a 60-cell polysilicon module with a specification of 275W under different light intensities. The product of current and voltage at each point on the curve reflects the output power of the module under this working condition.
In order to facilitate installation, installation holes and grounding holes are generally designed on the component frame, as shown in Figure 2. There are 4 mounting holes on each component, and the component and support structure can be directly fixed through the mounting holes. The ground hole is used for grounding the metal part of the component to meet electrical safety requirements.