1. What is the optimal capacity ratio
The capacity ratio of a PV inverter is the ratio between the rated capacity of the PV array and the rated capacity of the inverter. For instance, if the rated capacity of the PV array is 100kW and the rated capacity of the inverter is 80kW, then the capacity ratio is 1.25:1.
Optimal capacity ratio: the capacity ratio enabling the PV power system to realize the maximum power generation, the highest reliability and the best cost-effectiveness in a specific application scenario. Determination of the optimal ratio needs comprehensive consideration of a number of factors such as geographic location, climatic condition, characteristics of PV module, inverter performance, and system cost.
2.Range of Tolerance Ratio
Tolerance ratios are normally in the range of 1:1 to 1.5:1, though actually much larger. A small tolerance ratio means that a relatively large capacity inverter is fitted, which better withstands the fluctuation in the output of a PV array. However, doing so may result in poor inverter utilization and increased system costs. A higher tolerance ratio increases the utilization of the PV square array and reduces the system cost, but it may increase the risk of overloading the inverter and affect the reliability of the system. In determining the range of tolerance ratio, the following factors have to be considered:
The output characteristic of the PV module includes the maximum power point voltage, current, and temperature coefficient of different types of PV modules. These will determine the output power of the PV square array and the degree of inverter matching.
Performance parameters of the inverter: Rated capacity, maximum input power, efficiency curve, and other performance parameters of the inverter will also affect the selection of the tolerance ratio. For example, some inverters have higher overload capacity and can support higher tolerance ratios.
Geographical location and climate: Solar radiation intensity, temperature, humidity, and other climatic conditions differ in different regions, which will influence the output power of the PV array and the efficiency of the inverter. In areas with high solar radiation intensity, higher tolerance ratios can be considered.
System cost and benefit: The capacity ratio of the selection also needs to consider the cost and the benefit of the system. Higher ratios can reduce the cost of the system, which may affect the reliability and power generation of the system. Therefore, it is needed to weigh the cost and benefit and choose the most appropriate capacity ratio.
3. Influencing Factors
Geographical location and climatic condition
Solar radiation intensity: The greater the solar radiation intensity, the greater the output power of the PV array, and the higher the tolerance ratio that needs to be selected. Temperature: Temperature has a great influence on the output power of photovoltaic modules. In a high-temperature environment, the output power of the photovoltaic module will decrease, and a lower capacity ratio needs to be selected.
Humidity: The surface of the PV module easily condenses in high-humidity areas, which has a great influence on power generation efficiency. Therefore, attention should be paid to the selection of waterproof performance when selecting the type of PV module and inverter; at the same time, it is appropriate to reduce the tolerance ratio.
Characteristics of photovoltaic modules
Power level: Different power level photovoltaic modules have different output characteristics, and appropriate capacity ratio shall be determined according to the actual situation.
Temperature coefficient: the smaller the temperature coefficient of a PV module is, the smaller its output power influenced by temperature will be; therefore, a higher ratio of tolerance can be adopted. Attenuation rate: the lower the attenuation rate of a PV module, the better its long-term power generation performance, therefore a higher ratio of tolerance can be adopted. Inverter performance
Rated capacity: The inverter-rated capacity is decided by the maximum input power that an inverter could bear. You need to choose the appropriate capacity ratio according to the output power of the PV array and the rated capacity of the inverter.
Efficiency curve: The efficiency curve of an inverter impacts the working efficiency of the power generation system. While choosing a capacity ratio, the characteristics of the efficiency curve need to be taken into account, and then a ratio selected that can help the system generate electricity at the highest possible efficiency.
Overload capacity: Different inverters are designed with different overload capacities, meaning that some support higher ratios than others. An inverter's overload capacity must be considered to ensure system reliability during its selection.
System costs and benefits
Initial investment cost: Higher tolerance ratios can decrease the cost of PV arrays, but increase the inverter cost. The balance between initial investment cost and system performance needs to be struck to find the proper capacity ratio.
Long-term power generation benefit: The capacity ratio can improve the utilization of the PV array and increase the power generation of the system with a higher value. However, the overload risk of the inverter and the reliability of the system should be considered to ensure the long-term power generation benefit.
4. Design Principles
Meet system performance requirements
The system shall operate stably under the condition of the different weather conditions to reach the purpose of maximum power generation of the PV power generation system. The efficiency and reliability of the inverter have to be considered to prevent overload, overheat, etc. Cost and Benefit Consider the cost-benefit at system design and reduce the investment cost and operating and maintenance cost on the condition of achieving the requirements of system performance.
Improve the long-term power generation efficiency of the system and maximize the return on investment.
Flexible adaptation to different application scenarios
According to different geographic locations, climate conditions, PV module characteristics, and user needs, select the appropriate capacity ratio.
Consider the scalability and upgradability of the system so that the capacity ratio can be easily adjusted when needed in the future.
Follow relevant standards and codes.
The design process shall follow the relevant national and industry standards and norms to ensure the safety and reliability of the system.
Domestic and foreign advanced design experience and cases should be referred to and the design scheme continuously optimized.
The optimal capacity ratio of the PV inverter is complex to determine because it comprehensively considers a number of factors, such as geographical location, climatic conditions, characteristics of PV modules, performance of inverters, and costs and benefits related to the system. In the design process, determine the most appropriate capacity ratio that can meet the demands of system performance, think over the cost and benefit of the system, and flexibly meet the requirements of different application scenarios in accordance with relevant standards and specifications to achieve maximum power generation, the highest reliability, and the best economic performance of the photovoltaic power generation system.
We hope this article will help you in the selection and design of PV inverter capacity ratio. If you have any questions or suggestions, please feel free to leave a message in the comment section.
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