Factors affecting the output characteristics of photovoltaic cells and components
Since the output power of photovoltaic cells and components depends on the solar light intensity, the distribution of the solar spectrum, and the temperature, shadow, and crystal structure of the photovoltaic cell. Therefore, the measurement of photovoltaic cells and components is carried out under standard conditions (STC), and the measurement conditions are defined by the European Commission as No. 101, with the following conditions: spectral irradiance of 1000 watts/square meter; spectrum AM 1.5; battery temperature of 25 degrees Celsius .
Under this condition, the maximum power output by the solar photovoltaic and battery modules is referred to as peak power, and its unit is expressed as watts (Wp). In many cases, the solar cell's illumination and temperature are constantly changing, so the peak power of the component is usually measured with a simulator and compared to a standardized photovoltaic cell from an international certification body.
(1) The effect of temperature on the output characteristics of photovoltaic cells and modules
As we all know, when the temperature of photovoltaic cells and components is high, the work efficiency is degraded. As the temperature of the photovoltaic cell increases, the open circuit voltage decreases. In the range of 20-100 degrees Celsius, the voltage of the photovoltaic cell decreases by about 2 mV for every 1 degree Celsius increase; while the photocurrent rises slightly with the increase of temperature, about every Increasing the temperature of the battery by 1 degree Celsius increases by a thousandth. In general, for every 1 degree Celsius increase in temperature, the power is reduced by 0.35%. This is the basic concept of temperature coefficient. Different photovoltaic cells have different temperature coefficients, so the temperature coefficient is one of the evaluation criteria for photovoltaic cell performance.
(2) Influence of light intensity on the output characteristics of photovoltaic cells
The light intensity is proportional to the photocurrent of the photovoltaic cell and the module. In the range of 100-1000 watts per square meter, the photocurrent always increases linearly with the increase of light intensity; while the light intensity has little effect on the voltage, at the temperature. Under fixed conditions, when the light intensity varies from 400-1000 w wm, the open circuit voltage of the photovoltaic cells and components remains basically unchanged. Therefore, the power and light intensity of the photovoltaic cell are also basically proportional.
(3) Influence of shadow on photovoltaic cell and component output characteristics
The effect of shadows on the performance of photovoltaic cells and components cannot be underestimated, and even local shadows on photovoltaic components can cause significant reductions in output power. Therefore, care should be taken to avoid the generation of shadows and clean the surface of the components in time to prevent the hot spot effect. When a single battery is completely blocked, the solar cell module output is reduced by about 75%. Although the components are equipped with diodes to reduce the effects of shadows, if the effects of local shadows are underestimated, the performance and investment efficiency of the completed PV system will be greatly reduced.
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