Tips for Replacing PV Modules in Existing Power Stations and Solutions to the Dilemma of Spare Parts (1)
For the existing photovoltaic power plants built and put into operation in the early stage, with the passage of the operation time of the power plant, the photovoltaic modules will inevitably have replacement problems caused by factors such as serious power attenuation, module damage, and related safety hazards. According to the feedback from the operation and maintenance personnel of some photovoltaic power plants, the main difficulties in component replacement are:
* As the photovoltaic modules on the market have been gradually replaced by high-power modules, the low-power modules of the same type on the power station have been withdrawn from the market.
* Even if there are spare parts in stock, there will be potential current mismatch problems if only a few components are replaced sporadically within the same string.
* In the absence of spare parts, having to replace older components with higher power components will present significant current mismatch issues.
In the face of the above problems, the following replacement ideas are proposed in this paper, which can not only help the power station to solve the problem of zero spare parts, but also reduce the mismatch and improve the power generation of the string.
This idea is mainly based on the fact that the capacity ratio of early photovoltaic power plants is low, and the modules have a certain attenuation. For string inverters, all branches of the string inverter or all components under a certain MPPT can be "batch replaced" with high-power components. For centralized inverters, local components can be replaced in batches, so that a more reasonable capacity ratio can be obtained, and the power generation can be increased.
At the same time, the removed photovoltaic modules can be used as spare parts after testing.
Solution of Photovoltaic modules
For photovoltaic power plants using string inverters, the following points need to be considered during specific implementation:
1) If the size of the new module is different from the original module, it is necessary to estimate the number of installations based on the length of the existing photovoltaic support.
2) Evaluate whether the original photovoltaic compact size is suitable and whether it is necessary to purchase compacts that match the new modules.
3) Whether the load of the photovoltaic support is satisfied.
4) If the size of the new module is different from the size of the original module, since the distance between the front and rear rows of the array is designed based on the size of the old module, whether the shadow loss caused by the installation of the new module will increase for the front and rear rows.
The PVsyst software can be used for simulation calculation to simulate the power generation before and after component replacement and analyze the power generation gain.
5) After the number of installable components is determined, the number of components designed for the string can be evaluated according to the allowable voltage range of the inverter. If the optimal number of components in a series cannot be achieved, it can be appropriately reduced.
6) For the multi-row installation of components, different wiring methods, such as the commonly used in-line type, C type, etc., will cause different shadow losses caused by the front and rear rows of components. This loss should be minimized, and a favorable string wiring method should be adopted after evaluation.
7) Make full use of the multi-channel MPPT tracking function of the string inverter and optimize the access method from the string to the inverter.
8) After the module is replaced, the rated capacity of the string has changed. Correspondingly, the string capacity of the operation and maintenance management platform should also be adjusted. The photovoltaic power station capacity of the whole station should be updated accordingly.
