Photovoltaic Class: How to configure the power of components and grid-connected inverters

Some readers are asking, what equipment is related to the module power and how should it be designed? In the photovoltaic grid-connected system, the module power is related to the inverter, and the power matching between the module and the inverter is not a fixed ratio of 1:1. It needs to be considered comprehensively based on the specific situation of the project. The main influencing factors include irradiance, system loss, inverter efficiency, inverter life, inverter voltage range, module installation angle and other aspects.

1. Component installation inclination angle and azimuth angle

When the plane of the object is completely perpendicular to the light, the received power is the largest. If the object is tilted and the plane of the object and the light form a certain angle, the received power will be discounted. For the same area, the received power will be much less. When the angle between the component and the sun is perpendicular, the power is the largest.

2. Irradiance of the installation area

The output power of the module is related to the irradiance. In areas with good solar energy resources, due to the few clouds on sunny days, good air quality and high atmospheric transparency, the radiation from the sun reaching the surface of the module is much higher than the average value in areas with poor resources.

3. Installation altitude

The higher the altitude, the thinner the air is, and the less the atmosphere weakens the solar radiation, so the stronger the solar radiation reaching the ground is. For example, the Qinghai-Tibet Plateau is the area with the strongest solar radiation in my country. The thinner the air is, the worse the inverter heat dissipation is. When the altitude exceeds a certain height, the inverter must be derated.

4. DC side system efficiency

In a photovoltaic system, energy is radiated from the sun to the photovoltaic module, and then passes through the DC cable, combiner box, and DC power distribution to the inverter. There are losses in each link. Different design schemes, such as centralized, string, and distributed schemes, have very different DC side losses.

5. Inverter heat dissipation conditions

The inverter should generally be installed in a well-ventilated place away from direct sunlight, which is conducive to heat dissipation. If the inverter has to be installed in a closed place that is not conducive to heat dissipation due to site restrictions, the inverter derating problem should be considered and fewer components should be used.

6. Component Factors

Positive power tolerance: In order to ensure that the attenuation of photovoltaic modules does not exceed 20% in 25 years, many module manufacturers have a positive tolerance of 0-5% for modules that have just left the factory. For example, the actual power of a 265W module may be 270W when it leaves the factory.

Negative temperature coefficient: The power temperature coefficient of the module is about -0.41%/℃. When the module temperature drops, the module power will increase. Without considering the equipment loss, a 250W module may have a maximum output power of more than 250W in the areas with the best sunshine in my country, such as northern Ningxia, northern Gansu, southern Xinjiang, etc.

Bifacial modules: Bifacial modules can not only receive the radiation power of sunlight on the front side, but also the reflected radiation power of sunlight on the back side. Different objects have different reflectivity to sunlight in different spectral bands. Snow, wetlands, wheat, deserts, different objects have different reflectivity in the same band, and the same object also has different reflectivity in different bands.

7. Inverter factors

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. At 40% to 60% power, the efficiency is the highest. When it exceeds 60%, the efficiency gradually decreases. Therefore, the total power of the photovoltaic power should be controlled between 40% and 60% of the inverter power to obtain the best efficiency.

Inverter life: Photovoltaic inverters are electronic products, and their reliability is closely related to the inverter operating temperature. If the temperature of components such as capacitors, fans, and relays increases by 10°C, the failure rate will increase by more than 50%. The operating temperature is related to power. According to statistics, the life of an inverter that works at 80-100% power for a long time is about 20% lower than that of an inverter that works at 40-60% power.

The best operating voltage range of the inverter: The operating voltage is around the rated operating voltage of the inverter, with the highest efficiency. For a single-phase 220V inverter, the rated inverter input voltage is 360V; for a three-phase 380V inverter, the rated inverter input voltage is 650V.

in conclusion

In some places, the capacity of the photovoltaic system is calculated according to the capacity of the components. At this time, the inverter is selected according to the maximum power actually output by the components to avoid inverter current limiting. According to the actual situation, the components and inverters can be configured at 0.9:1 to 1.4:1. However, in some places, the system capacity is calculated according to the AC output power of the inverter. If the electricity price is high and the component price is quite cheap, in order to increase the power generation as much as possible, the power of the components can be increased. The components and inverters can be configured at 1.4:4 to 1.8:1, depending on how many components the inverter can connect.