In order to reduce the pressure, the power grid puts forward requirements for the output stability of photovoltaic power stations, which has become a general trend. For example, Germany has proposed a maximum climbing rate of 10% per minute, that is, every moment and a minute ago, the difference in power output of photovoltaic power plants can not be higher than 10%. The newly introduced grid-connected standards in many countries require photovoltaic power plants to have the requirements of power failure and reduced output when necessary, as well as smooth climbing rate. In cloudy weather, a 50% climb rate is also common, so it must be dealt with (see figure below). Power electronics technologies such as component optimizers and micro-inverters can be smoothed to a certain extent, but the processing capacity is very limited, and the solution to the problem is simple and rough, either to let the component power generation deviate from the optimal power point, or to cut off excess output, in order to achieve the requirements of grid stability. At this time, the energy storage system is the key to play a role: once the electricity generation surges, it will charge (rather than directly cut off the excess power generation); Once the power generation explodes, it is discharged to achieve continuous and stable power generation on the grid.

Three important indicators of chemical energy storage materials and devices, one is the energy density, related to the continuity of charge and discharge; The second is power density, which is related to the ability to release energy instantaneously; The third is the number of charge and discharge, which determines the life of the energy storage device. The following figure shows the energy density, power density and charge-discharge life of lead-acid batteries, lithium batteries, lithium-ion capacitors, carbon-based electrochemical double-layer capacitors EDLC, and electrolyte capacitors. Unfortunately, such extremely demanding application scenarios as photovoltaic have very high requirements for energy, power and life of the energy storage system! The energy storage capacity and charge and discharge power of the energy storage system directly affect the control of the climbing rate.