When a company installs a BESS with backup capabilities, one of the most common questions is: what should happen when the grid fails?
Not every installation requires the same level of continuity. Some processes can tolerate a few seconds of downtime, while in others even a very brief interruption can cause a production shutdown, product loss or problems with control systems. This is where an STS (Static Transfer Switch) can come into play.
What is an STS?
An STS is a system that allows an electrical load to be transferred from one power source to another in a very short period of time. Unlike other mechanical switching systems, it uses power electronics, allowing the transfer to take place within milliseconds. In an industrial installation, the two sources could be, for example, the electrical grid and a BESS.
Installing a BESS does not automatically guarantee that the plant will continue operating in the event of a grid outage. To achieve this, the entire architecture must be assessed: which loads need to remain operational, how much power they require, how much interruption time they can tolerate, whether the PCS can operate in island mode, how the system disconnects from the grid, and how the protection systems are coordinated.
An STS can be part of this architecture, but it is not a complete solution on its own.
When does it make sense to install one?
Mainly when there are loads that are highly sensitive to interruptions:
- PLCs and control systems
- automated production lines
- servers and IT systems
- continuous processes
- equipment where even a very short power interruption can cause a shutdown or restart
In these cases, the key question is not only how long the outage lasts, but what impact that outage has on the company’s operations. A two-second interruption can ultimately result in thirty minutes of downtime.
STS or ATS?
Both systems allow loads to be transferred between two power sources. The main difference is that an ATS typically uses electromechanical components, while an STS uses power electronics and can perform the transfer much faster. This does not mean that an STS is always the best option. If the process can tolerate the transfer time of an ATS, there may be no need to introduce a more complex solution.
At Solventa6, before proposing an STS or any backup system, we first analyse one key question: which loads are truly critical and what level of continuity do they require?
Separating critical loads from non-critical ones can prevent the BESS from being oversized and allows us to design a more technically and economically efficient solution. Because in a BESS project, it is not only about deciding how many kWh of battery capacity to install. It is about defining what we want to keep running when the grid stops supplying power.
