In the PV grid-connected system, the power of the module and the inverter are related, and the power matching between the module and the inverter is not a fixed ratio of 1:1, but needs to be considered in conjunction with the specific conditions of the project. The main influencing factors are irradiance, system loss, inverter efficiency, inverter life, inverter voltage range, module installation angle, etc.
1, module installation tilt angle and orientation angle
When the plane of the object and the light is completely perpendicular, the power received is the maximum, if the object is placed at an angle, the plane of the object and the light into a certain angle, the power received will be discounted, the same area, the power received will be much less, the angle of the component and the sun is perpendicular, the power is the maximum.
2、Irradiance of the installation area
The output power of the module and irradiance related. Solar energy resources in good areas, due to clear days with few clouds, good air quality, high atmospheric transparency, the sun's radiation reaching the surface of the module is much higher than the average value of poor resources.
3, installation altitude
The higher the altitude, the thinner the air, the weaker the atmosphere on the solar radiation, the stronger the solar radiation reaching the ground. For example, the Qinghai-Tibet Plateau is the strongest area of solar radiation in China. And the thinner the air is, the worse the inverter heat dissipation is, and the altitude exceeds a certain height, the inverter should be derated to run.
4、DC side system efficiency
Photovoltaic system, energy from solar radiation to photovoltaic modules, through the DC cable, converter box, DC distribution to reach the inverter, in which each link has losses,. Different design solutions, such as the use of centralized, string, decentralized and other programs, DC-side losses are very different.
5、Inverter cooling conditions
The inverter should generally be installed in a well-ventilated place to avoid direct sunlight, which is conducive to heat dissipation. If, due to site constraints, the inverter has to be installed in a closed place that is not conducive to heat dissipation, we should consider the derating problem of the inverter and allocate fewer components.
6, component factors
Power positive tolerance: in order to meet the PV module attenuation of 25 years not more than 20%, many component factories have 0-5% positive tolerance for components just leaving the factory, such as 265W components, just leaving the factory the actual power may have 270W.
Negative temperature coefficient: The power temperature system of the module is about -0.41%/°C. The power of the module will rise when the temperature of the module drops. A 250W module, without considering the equipment loss, in the best sunny areas of China, such as northern Ningxia, northern Gansu, southern Xinjiang, etc., it is possible that the maximum output power may exceed 250W.
Double-sided modules: Double-sided modules can not only receive the radiation power of sunlight on the front side, but also receive the reflected radiation power of sunlight on the back side. Different objects, in different spectral bands, have different reflectivity of sunlight. Snow, wetland, wheat, desert, different features in the same band its reflectivity is different, the same feature in different bands reflectivity is also different
7、Inverter factor
Inverter efficiency: the efficiency of the inverter is not a constant value, there are power switching device losses and magnetic losses, at low power, the efficiency is relatively low, in 40% to 60% power, the efficiency is the highest, more than 60%, the efficiency gradually decreases. Therefore, the total power of PV power should be controlled between 40% and 60% of the inverter power to obtain the best efficiency.
Inverter life: PV inverter is an electronic product, its reliability and inverter operating temperature has a lot to do with it, where capacitors, fans, relays and other components temperature increase by 10 ℃, the failure rate can be increased by more than 50%. And the operating temperature is related to the power, according to statistics, the inverter long-term work in power 80-100% than power 40-60%, life expectancy is about 20% lower.
The best operating voltage range of the inverter: working voltage around the rated operating voltage of the inverter, the highest efficiency, single-phase 220V inverter, the inverter input rated voltage of 360V, three-phase 380V inverter, the inverter input rated voltage of 650V.
Conclusion
In some places, the PV system is based on the capacity of the module to calculate the system capacity, this time according to the actual maximum power output of the module to select the inverter, so as to avoid inverter current limit, according to the actual situation, the module and inverter can be 0.9:1 to 1.4:1 to configure. However, in some places, the system capacity is calculated according to the inverter AC output power. If the selling price of electricity is high and the module price is quite cheap, the power of the module can be increased in order to increase the power generation as much as possible. Modules and inverters can be configured from 1.4:4 to 1.8:1, depending on how many modules the inverter can connect.
