The energy transition is in full swing, but in order to substantially speed it up we need smart solutions for storing energy. S4 Energy’s latest contribution, a unique combination of kinetic and chemical storage, is proving its usefulness on the ground: by helping TenneT TSO stabilise the Dutch grid.

As a specialist in energy storage, S4 Energy develops tailor-made solutions for a wide range of clients: from TSOs and DSOs to renewable energy producers and industrial users. “We build integrated solutions using various kinds of existing technology”, says Dominique Becker Hoff, director of projects. “However, we’ve also developed a new, proprietary technology. Our KINEXT units are built around an unusually large and efficient flywheel. Compared to existing flywheels, they have a much higher storage capacity, and can deliver large amounts of power, for minutes if necessary. And thanks to specially developed algorithms, they offer an exceptionally short response time, within milliseconds.”

Regulating high-voltage grids

KINEXT technology has a variety of use cases. One of the first customers to spot its potential was Dutch grid operator TenneT TSO. S4 Energy recently started providing FCR services to help TenneT deal with sudden frequency fluctuations, using a unique combination of KINEXT units, battery systems and algorithms which ensure that both technologies are used to their maximum potential.


Becker Hoff: “There’s a growing demand for frequency containment reserve throughout Europe, as more renewable energy sources feed into the grid. Especially since much FCR capacity is currently provided by coal-fueled electricity plants, which will be phased out at some point in the near future.”

Maximizing profits

S4 Energy certainly is prepared for a growing demand: the company has invested in a dedicated facility which can produce over 50 KINEXT units per year.


Not just for TSOs and DSOs, Becker Hoff emphasizes. “Grid stabilization is a major application of this technology, but certainly not the only one. For example, we’re currently in talks with a wind farm operator. A KINEXT unit could be used to store surplus energy on site, which can then be used to stabilize output. In combination with the efforts of grid operators to match supply and demand, we’re convinced this can make onshore wind turbines more profitable, even without subsidies.”

Another area in which smart storage technology can help maximize profits, is by regulating energy consumption in an industrial setting. Industrial facilities often face short, sudden voltage fluctuations, which may be caused by their own equipment or which ‘enter’ the site through their grid connection. It’s a costly problem, Becker Hoff says. “It may result in substantial fines by the grid operator, and in a worst-case scenario it may bring production to a halt. Our solution can minimize this risk by regulating energy consumption much more effectively. One of its main USPs is the speed with which the system can intervene: it can store and release large amounts of energy in milliseconds.”

Carbon footprint reduction

An added bonus for large-scale energy consumers is that KINEXT technology can reduce their environmental impact. “Traditional UPS systems, for example, largely rely on diesel generators. Smart energy storage can reduce or even eliminate a site’s dependence on diesel. So far, a major constraint on such storage-based UPS systems was their complexity. Typically, they consisted of a large number of smaller flywheels and/or batteries. The key advantage of our solution is its size, power and speed. A single KINEXT unit has the power and response time needed to quickly smooth out most fluctuations. In other words, it can act as a first line of defence in case of a power outage, taking the strain off battery systems and substantially extending their lifespan. Which means the whole set-up becomes more robust, more efficient. And in the long run, again, saves money.”