Is STS Always Needed for Peak Shaving?

When the energy storage system is only used for peak shaving and valley filling, the STS (static transfer switch) grid-connected and off-grid switching system is not necessary, and the specific judgment needs to be made according to the application scenario and demand.

The following is a comprehensive analysis:

1. The relationship between the core function of peak shaving and valley filling and STS

Peak shaving and valley filling mainly optimizes electricity costs by charging the energy storage system during the low electricity price period and discharging during the peak period. Its core is the charging and discharging strategy and economic scheduling, which belongs to the energy management category under the grid-connected operation mode. At this time:

- Only grid-connected operation is required: the energy storage system is connected to the grid through the PCS (converter), and automatically charges and discharges according to the time-of-use electricity price strategy, without frequent switching of grid-connected and off-grid states.

- Conditions without STS: If the system only needs to respond to the price difference and the power supply of the grid is stable (no frequent power outage risk), the STS grid-connected and off-grid switching function is not necessary.

2. The role and application scenarios of STS

STS is mainly used to quickly switch to off-grid mode when the grid is abnormal (such as power outage or voltage fluctuation) to ensure continuous power supply to critical loads. Its necessity depends on the following scenario requirements:

- High power supply continuity requirements: For example, hospitals, data centers or high-tech manufacturing industries require millisecond switching (such as within 2ms) to avoid production interruptions or equipment damage.

- Low grid reliability: In areas with frequent grid failures or power restrictions (such as seasonal power outages in plateau forests), STS can be combined with energy storage systems to achieve seamless switching and improve power supply reliability.

3. Economic and technical trade-offs

- Cost considerations: STS systems will increase equipment investment and complexity. If only peak shaving and valley filling are required, there is no need to pay extra hardware and operation and maintenance costs for STS.

- Technical simplification: The peak shaving and valley filling function can be controlled separately by EMS (energy management system), without involving complex logic of on-grid and off-grid switching.

4. Exceptions

If peak shaving and valley filling need to be combined with **demand side response** or **virtual power plant** functions (such as participating in grid dispatching or reserve capacity trading), STS may become an auxiliary tool to support rapid response to grid instructions, but such requirements have exceeded the scope of simple peak shaving and valley filling.

Summary

- Scenarios where STS is not needed: industrial and commercial users with stable power grids, no need for high-reliability power supply, and only seeking electricity price arbitrage.

- Scenarios where STS is needed: complex systems with frequent power grid fluctuations, need to ensure the continuity of power supply to key loads, or need to expand functions (such as demand response).

When making actual choices, it is recommended to conduct a comprehensive assessment based on the specific power consumption environment, load characteristics, and investment budget.