As photovoltaic poverty alleviation efforts deepen, many problems have begun to emerge. For example, in some remote areas, construction workers have found that the grid voltage is consistently too high during grid connection, triggering frequent voltage fault alarms and causing inverter shutdown protection, severely impacting photovoltaic revenue. To address this issue, manufacturers often provide solutions from the inverter side, such as widening the protection voltage range (adjusting the factory AC voltage to 160-300 AC for different regions). While this method solves the inverter's shutdown protection problem, the excessively high grid voltage output can still damage some household appliances.
This phenomenon is quite common, and many forum posts have provided professional technical analyses, yet many practitioners still express confusion. Here, I would like to offer a simple explanation through some analogies to help everyone avoid these situations from the very beginning of power plant design.
As we all know, a photovoltaic grid-connected system is the process of converting direct current (DC) into alternating current (AC) through an inverter and transmitting it to the power grid. If we compare the power grid to the ocean, the inverter can be seen as streams, and grid connection is like these streams flowing into the ocean, while the AC cables used for grid connection are the riverbeds where these streams converge.
To illustrate this, let's draw an analogy:
In some remote areas or areas with weak power grids, during grid-connected power generation, the output AC voltage of the inverter often has to be increased due to the influence of line impedance (narrow riverbeds, many blockages) to ensure that the AC power flows efficiently to the grid (rivers flow into the sea). However, this can lead to two problems: first, the output voltage may exceed the inverter's own protection voltage, causing the inverter to report errors and execute protective shutdowns; second, the capacity of the transformer at the grid connection point may be small (i.e., "insufficient water storage in the sea," which is why many places limit grid connection capacity to around 30%), making it easy for the power to overload and raise the grid voltage (like an insufficient reservoir overflowing).
In fact, the above two situations are the two main reasons for excessively high grid voltage: insufficient grid connection capacity leading to inadequate load consumption, or a weak grid highlighting line impedance. So, how can we solve these problems?
Undoubtedly, the solutions are twofold: first, increase the cable specifications and select appropriate grid connection points; second, increase the capacity of transformers to improve "water storage capacity." The latter two are easy to understand: selecting a grid connection point near the nearest transformer is the most common method, and increasing transformer capacity simply means increasing the capacity of existing transformers. This leaves only increasing the cable specifications. To use a vivid analogy, this is like widening the riverbed and clearing silt near the sea to significantly reduce resistance in the middle of the river.
Another situation worth mentioning is that when multiple devices are connected to the grid, if they are all connected to a single phase, it can easily raise the voltage of that phase (similar to multiple rivers flowing into a narrow riverbed, causing overflow), leading to a bias in the grid voltage and resulting in a phenomenon similar to excessive grid voltage. Therefore, it is recommended that when multiple devices are connected to the grid at the same connection point, the devices should be distributed as evenly as possible across the three phases (as shown in the figure below).
The above aims to provide a simple analogy to give everyone a vivid understanding of the causes of power grid overvoltage faults. However, the ultimate goal is to avoid these potential hazards from the initial design stage of photovoltaic power plant construction, thereby improving design efficiency and contributing to poverty alleviation through photovoltaic power.
