As the global demand for renewable energy continues to grow, photovoltaic power generation technology has developed rapidly. As the core carrier of photovoltaic power generation technology, the photovoltaic power station's design rationality directly affects the power generation efficiency, operational stability and economic benefits of the power station. Among them, the capacity ratio is a key parameter in the design of photovoltaic power stations and has an important impact on the overall performance of the power station.
01
Overview of photovoltaic power station capacity ratio
Photovoltaic power station capacity ratio refers to the ratio of the installed capacity of photovoltaic modules to the capacity of inverter equipment. Due to the instability of photovoltaic power generation and the large impact of the environment, the capacity ratio of photovoltaic power stations simply configured according to the installed capacity of photovoltaic modules at 1:1 will cause a waste of photovoltaic inverter capacity. Therefore, it is necessary to increase the capacity of the photovoltaic system under the premise of stable operation of the photovoltaic system. For photovoltaic system power generation efficiency, the optimal capacity ratio design should be greater than 1:1. Rational design of capacity ratio can not only maximize power generation output, but also adapt to different lighting conditions and cope with some system losses.
02
Main influencing factors of volume ratio
Reasonable capacity-to-distribution ratio design needs to be comprehensively considered based on the situation of the specific project. Factors that affect the capacity-to-distribution ratio include component attenuation, system loss, irradiance, component installation inclination, etc. The specific analysis is as follows.
1. Component attenuation
Under the condition of normal aging and attenuation, the current attenuation of modules in the first year is about 1%, and the attenuation of the modules after the second year will change linearly. The decay rate in 30 years is about 13%, which means that the annual power generation capacity of the module is decline, the rated power output cannot be maintained continuously. Therefore, the photovoltaic capacity ratio design must take into account the component attenuation during the entire life cycle of the power station to maximize the matching of component power generation and improve system efficiency.
2. System loss
In the photovoltaic system, there are various losses between the photovoltaic modules and the inverter output, including the loss of series and parallel components and shielding dust, DC cable loss, photovoltaic inverter loss, etc. The losses in each link will affect the inverter of the photovoltaic power station. the actual output power of the converter.
In project applications, PVsyst can be used to simulate the actual configuration and shading loss of the project; generally, the DC side loss of the photovoltaic system is about 7-12%, the inverter loss is about 1-2%, and the total loss is about 8-13%; Therefore, there is a loss deviation between the installed capacity of photovoltaic modules and the actual power generation data. If a photovoltaic inverter is selected based on the module installation capacity and a capacity ratio of 1:1, the actual maximum output capacity of the inverter is only about 90% of the rated capacity of the inverter. Even when the lighting is at its best, the inverter will Not working at full load reduces the utilization of the inverter and system.
3. Different areas have different irradiances
The module can only reach the rated power output under STC working conditions (STC working conditions: light intensity 1000W/m², battery temperature 25°C, air quality 1.5). If the working conditions do not meet the STC conditions, the output power of the photovoltaic module must be less than its rated power, and the time distribution of light resources within a day cannot all meet STC conditions, mainly because of the large differences in irradiance, temperature, etc. in the morning, middle and evening; at the same time, different irradiances and environments in different regions have different impacts on the power generation of photovoltaic modules. , so in the early stage of the project, it is necessary to understand the local lighting resource data according to the specific area and conduct data calculations.
Therefore, even in the same resource area, there are large differences in irradiation throughout the year. This means that the same system configuration, that is, the power generation capacity is different under the same capacity ratio. To achieve the same power generation, it can be achieved by changing the capacity ratio.
4. Component installation inclination angle
There will be different roof types in the same project of user-side photovoltaic power stations, and different roof types will involve different component design inclination angles, and the irradiance received by the corresponding components will also be different; for example, in an industrial and commercial project in Zhejiang There are color steel tile roofs and concrete roofs, and the design inclination angles are 3° and 18° respectively. Different inclination angles are simulated through PV and the irradiation data of the inclined surface are shown in the figure below; you can see the irradiation received by components installed at different angles. The degree is different. For example, if distributed roofs are mostly tiled, the output energy of components with the same capacity will be lower than those with a certain inclination.
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Capacity ratio design ideas
Based on the above analysis, the design of the capacity ratio is mainly to improve the overall efficiency of the power station by adjusting the DC side access capacity of the inverter; the current configuration methods of the capacity ratio are mainly divided into compensation over-provisioning and active over-provisioning.
1. Compensation for over-allocation
Compensating over-matching means adjusting the capacity-to-match ratio so that the inverter can reach full load output when the lighting is best. This method only takes into account part of the losses existing in the photovoltaic system. By increasing the capacity of the components (as shown in the figure below), the system losses during energy transmission can be compensated, so that the inverter can reach full load output during actual use. effect without peak clipping loss.
2. Active over-allocation
Active overprovisioning is to continue to increase the capacity of photovoltaic modules on the basis of compensating for overprovisioning (as shown in the figure below). This method not only considers system losses, but also comprehensively considers factors such as investment costs and benefits. The goal is to actively extend the full-load operating time of the inverter to find a balance between the increased component investment cost and system power generation revenue, so as to minimize the system's average level cost of electricity (LCOE). Even when the lighting is poor, the inverter still operates at full load, thereby extending the full-load operating time; however, the actual power generation curve of the system will have a "peak clipping" phenomenon as shown in the figure, and it will be at the limit during some periods of time. Send working status. However, under the appropriate capacity ratio, the overall LCOE of the system is the lowest, that is, the revenue increases.
The relationship between compensated over-matching, active over-matching and LCOE is shown in the figure below. LCOE continues to decrease as the capacity-matching ratio increases. At the compensation over-matching point, the system LCOE does not reach the lowest value. If the capacity-matching ratio is further increased to the active over-matching point, the system's LCOE LCOE reaches the minimum. If the capacity ratio continues to be increased, LCOE will increase. Therefore, the active over-distribution point is the optimal capacity ratio value of the system.
For the inverter, how to meet the lowest LCOE of the system requires sufficient DC side over-provisioning capability. For different regions, especially those with poor irradiation conditions, higher active over-provisioning solutions are needed to achieve extended inversion. The rated output time of the inverter can be maximized to reduce the LCOE of the system; for example, Growatt photovoltaic inverters support 1.5 times over-provisioning on the DC side, which can meet the compatibility of active over-provisioning in most areas.
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conclusion and suggestion
To sum up, both compensated overprovisioning and active overprovisioning schemes are effective means to improve the efficiency of photovoltaic systems, but each has its own emphasis. Compensatory over-provisioning mainly focuses on compensating system losses, while active over-provisioning focuses more on finding a balance between increasing investment and improving revenue; therefore, in actual projects, it is recommended to comprehensively select an appropriate capacity-provisioning ratio configuration plan based on project needs.