01-Why does centralized energy storage have security risks? We can explain it from the perspective of electrical energy dimensions.
Voltage and current are one-dimensional, simple voltage, if there is no current, there is no danger, such as 10KV, 220KV high-voltage lines, we use an insulator to contact, because the resistance is very large, there is almost no current, so there is no risk. In the same way, the simple current, if the voltage is very low, as low as 48V, it will not harm the human body.
Power is the product of voltage and current. It is two-dimensional. When the power reaches a certain level, it will be dangerous. In a photovoltaic system, components, inverters, switches, and cables all have power, so these devices must be protected, mainly for insulation protection and temperature protection.
Energy storage battery is the product of voltage, current and time. It is three-dimensional. It can store the energy emitted by photovoltaic modules for several hours or even days. It has the highest risk program in photovoltaic systems. Because in the event of an accident, the storage battery may release the energy stored in a few days within a few seconds, and the power may be amplified by tens to hundreds of times. If an accident occurs in centralized energy storage, it will be transferred and superimposed with each other, and the risk factor will increase with the capacity of the power station.
02-The safety risks of energy storage power stations can be explained from the perspective of equipment principles and protection.
The battery is divided into two polarities, positive and negative. The two poles must be insulated. The load and the battery must be electrically isolated to prevent conduction, because the load cannot be controlled by the energy storage station. This insulation and isolation mainly rely on insulating materials and electrical switches. However, the insulating material and the conductive material are not very strict, and they will be converted into each other under certain conditions. The insulating material may be carbonized at high temperature and become conductive material. The isolation switch may also break down under high pressure. The power device switch tube is Under reverse high voltage and surge impact, abnormal conduction may also be possible.
Power storage is the most effective way to solve the volatility of new energy sources such as photovoltaic and wind power, and photovoltaic wind power is the most critical way for the country to achieve the goal of carbon neutrality. From the perspective of the main path of carbon neutrality, in the power industry, photovoltaic power Energy storage is the main line of the entire power exploration. Therefore, although power storage encounters some difficulties, the state will not cancel it. Instead, it will increase its development and continue to move forward.
Centralized energy storage needs to be equipped with very strong safety protection measures, and the cost will be very high; the string distributed energy storage adopts a DC coupling method to disperse the energy storage batteries and place them together with the string inverters. This can reduce the risk of energy storage power stations.
Currently, there are two ways of photovoltaic energy storage:
One is centralized AC coupling, where photovoltaic power generation is first inverted into AC power, and then from the AC end into the storage battery through DC-AC conversion.
The other is the distributed DC coupling of the string, the photovoltaic power generation enters the storage battery through DC-DC conversion from the DC end.
At present, centralized energy storage basically adopts AC coupling, because the domestic grid-connected inverter technology and two-way PCS technology are very mature. DC coupling is mainly used for off-grid power stations and small grid-connected energy storage projects.