Photovoltaic module capacity and inverter capacity ratio are used as volume ratio. Reasonable ratio design needs to be considered in conjunction with specific project conditions. The main influencing factors include irradiance, system loss, inverter efficiency, inverter life, inverter voltage range, component installation angle, etc. On the other hand, since inverters only account for about 5% of the system cost, in distributed photovoltaic power plant systems, the number of inverters is reduced due to over-provisioning of components, and investment returns are low, which will bring other problems. as follows.

1, different areas of different irradiance

According to the division criteria of the Wind Energy Solar Energy Assessment Center of the National Meteorological Administration, China's solar energy resources regions are divided into four categories, and the irradiance varies greatly in different regions. Even in the same resource area, there is a large difference in the annual radiation amount in different places. For example, in the same type I resource area in Tibet's Muer and Qinghai's Golmud, Seoul's annual radiation is 7998 MJ/m2, which is 17% higher than that of Golmud's 6815 MJ/m2. Means the same system configuration, that is, the same volume ratio, the power generation in the Seoul region is 17% higher than Golmud. To achieve the same amount of power generation, you can achieve this by changing the volume ratio.

2, system loss

In the photovoltaic system, energy is radiated from the sun to the photovoltaic modules, and the inverters are reached through DC cables, combiner boxes, and DC power distribution, and all the links have losses. As shown in the figure, the DC loss is usually about 7-11%, the inverter loss is about 1-2%, and the total loss is about 8-13% (the system loss here does not include the transformer behind the inverter and Line loss section).

That is to say, in the case of equal component capacity and inverter capacity, the actual output maximum capacity of the inverter is only about 90% of the rated capacity of the inverter due to various kinds of objectively existing losses, even when the light is best. The inverter is also not fully loaded.

3, 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, and when the inverter exceeds 60%, the efficiency is gradually reduced. Therefore, the total power of photovoltaic power should be controlled between 40% and 60% of the inverter power to obtain the best efficiency.

4, the life of the inverter

Photovoltaic inverters are electronic products, and their reliability is closely related to the operating temperature of the inverter. The temperatures of capacitors, fans, relays and other components are increased by 10°C, and the failure rate can be increased by more than 50%. The operating temperature is also related to power. According to statistics, the inverter operates at a power of 80-100% for a long period of time and a power ratio of 40-60%, and the lifetime is about 20% lower.

5, the inverter's optimal operating voltage range

The working voltage is about the rated operating voltage of the inverter, and the efficiency is the highest. The single-phase 220V inverter, the input voltage of the inverter is 360V, the three-phase 380V inverter, and the inverter input voltage is 650V. Such as 3kW inverter, with 260W components, working voltage 30.5V, with 12 pieces of work voltage 366V, the total power of 3.12kW is the best. The 30KW inverter is equipped with a 260W module, followed by 126 modules, each with 21 strings, a voltage of 640.5V, and a total power of 32.76kW.

In summary, the system power is between 40-60% of the rated power of the inverter, with the highest efficiency and longest service life. In order to optimize the performance of the inverter, depending on the lighting conditions, the components and the inverter have different ratios.

In a type of lighting area, the average sunshine duration is more than 5 hours, and the power generation time is calculated as 10 hours per day. It is recommended that the components and inverters be configured at 1:1, with an average power of about 50%;

In the second lighting area, the average sunshine duration is 4 hours, and the power generation time is calculated as 9 hours per day. It is recommended that the components and inverters be configured in accordance with 1.1:1, (4*1.1)/9, and the average power is about 49%;

In the three areas of the lighting area with an average sunshine duration of 3.5 hours, the power generation time is calculated at 8.5 hours per day. It is recommended that the components and inverters be configured at 1.2:1 (3.5*1.2)/8.5 and the average power is about 49.4%.

In the three regions where the average sunshine duration is less than 3 hours, the power generation time is calculated as 8 hours per day. It is recommended that the components and inverters be configured at 1.3:1 (3*1.3)/8 with an average power of about 48.75%.

The orientation of mountainous power stations is different, and the complexity and orientation of distributed PV roofs are different. Therefore, PV modules do not face south, and the inclination angle of Caigang tile roof is not the best inclination angle. The configuration of the inverter can be flexibly handled according to the specific situation.

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