What is grid-connected energy storage?

What is grid-building energy storage? How does it differ from the more familiar grid-following energy storage?

In terms of concept, in power systems, grid-following generally refers to generators or equipment operating as synchronous generators, whose speed and phase must be synchronized with the grid. In other words, these devices must "follow" the grid's frequency and phase to ensure stable power supply.

Grid-building, on the other hand, refers to the ability of a generating device or system to operate independently without external grid support and maintain stable voltage and frequency to supply power to the load. Grid-building capabilities generally refer to devices capable of "building and forming a grid," allowing them to continue operating during grid failures or establish independent microgrids in remote areas.

Simply put, the differences between the two can be summarized as follows:

• Grid-following: Generators synchronize with the existing grid.

• Grid-building: Generators independently form a grid to supply power to the load.

As a revolutionary energy storage technology, the core of grid-building energy storage lies in its PCS, which can autonomously set voltage and frequency parameters, just like traditional generators, to create a stable voltage source. It not only stores electricity but also actively adjusts to grid fluctuations, providing inertia support, suppressing oscillations, and even independently building microgrids.

In general, first, a grid-connected electrochemical energy storage system should have grid control capabilities, providing inertia and short-circuit capacity. During steady-state and transient conditions, the voltage amplitude and phase angle at the terminals of the grid-connected electrochemical energy storage converter should be able to maintain a certain level of stability, capable of sharing unbalanced grid power, with a power response time of no more than 5 ms.

Second, the grid-connected electrochemical energy storage system should be able to receive and respond to AGC and AVC commands sent by the dispatcher. Third, the grid-connected electrochemical energy storage system should have a black start function. During the black start period, there should be no significant circulating current or oscillation between the individual converters, and the maximum deviation in the effective current value should be no more than 5%.

Fourth, the grid-connected electrochemical energy storage system should have a certain frequency and voltage tolerance, capable of maintaining operation within a frequency deviation of ±2 Hz. The voltage at the terminal of the energy storage unit should be able to be flexibly adjusted within a range of 0% to 130% according to system needs. Finally, the grid-related parameters of the grid-type electrochemical energy storage system are centrally managed by the grid dispatching department. Before the grid-type energy storage system is connected to the grid, the coordination of key grid-related parameters and network source parameters should be completed, and the on-site parameter measurements should be completed.