What is the DC/AC ratio of a PV system?

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There are many technical parameters that need to be considered when designing a PV system, such as tilt angle, azimuth angle, module spacing, DC/AC ratio and other equipment technical parameters, among which DC/AC ratio is a parameter that needs to be considered. A reasonable capacity ratio not only ensures that the equipment operates in the best condition, but also ensures the utilization rate of the modules, which is directly related to the investment and cost recovery of the PV system.

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What is the tolerance ratio?

Tolerance ratio refers to the ratio of module power to inverter rated output power in PV power plant. If the PV system is designed according to the 1:1 capacity ratio, but due to the light conditions and temperature, the PV modules do not reach the nominal power most of the time, the inverter is basically operating at non-full load, and the capacity is wasted most of the time. The over-allocation design is an effective means to improve the overall utilization rate of the PV system, reduce the system power cost and improve the revenue.

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Influencing factors of capacity allocation ratio

There are many factors influencing the tolerance ratio, including
 Insufficient irradiation intensity
 High ambient temperature
 Stains and dust shading
 module orientation is not optimal throughout the day (tracking brackets have less influence on this factor)
 module power decay
 Intra- and inter-string matching losses

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What is the principle of calculating the capacity matching ratio?

According to different principles, there are three types of tolerance ratios. The first category is low capacity allocation, that is, the inverter module side capacity is lower than the rated capacity of the inverter; the second category is compensation over allocation, the system will not appear power limit as the principle to increase the system capacity ratio; the third category is active over allocation, the system LCOE lowest as the principle to increase the system capacity ratio, because there will be power limit of the inverter, the system will lose part of the energy, but the comprehensive investment and output, the system's kWh cost will be the lowest. However, the system's cost per kWh will be the lowest. Moderate increase of module and inverter capacity ratio can not only improve the utilization rate of inverter, but also improve the economic efficiency of power plant. You can read "How to calculate the cost of electricity" by Maysun.

The main reason for over-matching is that the PV modules do not reach the ideal peak power in the actual operation process.

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The advantages of over-matching

Reducing system investment costs and improving investment returns is one of the main goals of PV power plant system design and optimization. High over-matching requirements are also high, such as the ability to take on DC power hardware, and the ability to dissipate heat for long hours of operation. You can read "Inverter selection and installation" compiled by Maysun

1. It can compensate for the lack of light, reduce the power loss caused by temperature, dust, module attenuation, etc. It can make the PV plant reach the rated output power and provide stable power to the grid.
2. The inverter works longer in the morning and evening hours. Since the inverter needs the DC input power to reach its start-up threshold before it can start. Therefore, under the same sunlight intensity, increasing the capacity ratio can make the PV module output higher power, the inverter starts earlier and stops later, and the power generation time is longer, which can make better use of the local light resources.
3. Improving the utilization rate of inverters, in-situ boosters, distribution and substation equipment, diluting the investment cost of utilities, significantly reducing the project cost and lowering the cost of power generation.

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