A hybrid energy storage system combining lithium-ion batteries with mechanical energy storage in the form of flywheels has gone into operation in the Netherlands, from technology providers Leclanché and S4 Energy.

Switzerland-headquartered battery and storage system provider Leclanché emailed Energy-Storage.news this week to announce that what began as a small-scale pilot of the twinned technologies has now gone to grid-scale and into commercial operation.

The hybrid system combines 8.8MW / 7.12MWh of lithium-ion batteries with six flywheels adding up to 3MW of power. It will provide 9MW of frequency stabilising primary control power to the transmission grid operated by TenneT and is located in Almelo, a city in the Overijssel province in the east Netherlands.

The system’s provision of services into the market will be managed by S4 Ancillary Services, a joint venture (JV) part-owned by flywheel manufacturer and supplier S4 Energy. S4’s partner in the JV is a local government-owned entity, Energiefonds Overijssel, which aims to accelerate the transition to clean energy in the province. Overijssel is targeting 20% renewables by 2023 and the storage system helps the local grid to manage increased shares of variable renewable generation.

“We believe that the combination of these two technologies provides a clear advantage for enhanced ancillary services and the further integration of renewables into the grid,” Leclanché VP for system engineering Daniel Fohr said.

Hybrid combination plays to complementary strengths of each technology
S4 Energy launched into the frequency containment reserve market using a combination of its KINEXT flywheels and batteries in 2017. According to the company’s project director Dominique Becker Hoff, the flywheel supplies instantaneous power for very short periods of time without losing capacity. The 5,000kg KINEXT flywheel operates at 92% efficiency, storing energy as rotational mass.

An ever increasing demand for quickly available and cost effective energy worldwide stands opposite the issues of climate change and growing environmental awareness in our society. As a consequence, the demand for improved technologies in the field of energy storage, especially with regard to regenerative energies, is ever rising. This development is a major booster for developing new technologies and innovative production processes in this area. The diversity of the particular applications thereby lets new technologies face various challenges. Depending on the time the energy needs to be stored, and the number of according charges and discharges, different technologies are to be considered – but all of them have one thing in common: they essentially depend on vacuum technology.

Vacuum for flywheel technology

The short-term storage of energy has shortly been revolutionized by an innovative technology: mechanical flywheel energy storages. They are used as stationary or mobile systems in different applications. Part two of the series on “vacuum for energy storage” by Pfeiffer Vacuum focuses on stationary flywheel systems. Stationary flywheel systems are, for example, used as Uninterruptible Power Supply (UPS) in data storage centers and hospitals. Moreover, grid balancing tasks – which become more and more important due to an increased use of solar and wind energy – can also be supported by flywheel systems. A long lifetime even when facing many load cycles as well as the possibility to provide the stored energy instantly when needed make them the ideal choice for this application. Although the basic principle of saving energy through a rotating mass can easily be understood, designing an efficient and safe system is quite challenging.

Design of a flywheel mass storage

One of the main components of a flywheel is its rotor. It is usually either made of tempering steel or fiber-reinforced synthetics. The choice of the right material is demanding. Requirements are a high specific tensile strength to withstand the enormous forces as well as a low elastic modulus to keep the tight tolerances and to allow a high energy density, just to name a few. The rotational speed of the rotor can be several ten thousands of rotations per minute – some models even reach up to ninety thousand rotations per minute. Therewith, a high energy density can be reached.

Convergent Energy + Power, a US-Canadian project developer which has attracted investment from the venture capital arm of Statoil, has acquired 40MW of flywheel energy storage already in operation in grid-balancing markets in New York State and Pennsylvania.

Rockland Capital, an investment company focused on the energy sector in North America, acquired renewables integrator Beacon Power in 2012 and in doing so created a limited liability entity, Stephentown Spindle, to develop a 20MW flywheel project in Stephentown, New York. Spindle then went on to also develop the second 20MW flywheel project, Hazel Spindle, in Hazle Township, Pennsylvania.

The former went into operation in 2011, the latter in 2014, providing frequency regulation to the transmission networks of PJM Interconnection and New York ISO (Independent System Operator), bringing Convergent’s portfolio of energy storage assets in North America up to 66.5MW across seven projects.

The flywheels, which store power as rotational energy, can respond to grid signals in a fraction of the time it takes fossil fuel generators or nuclear, and do so cleanly. While not as fast-responding as lithium batteries, the wheels, in this case 400 of them weighing five tonnes each, experience little degradation over time and theoretically require less maintenance. With increasing amounts of variable renewable energy generation in North America, there is an increasing need to balance the frequency of grids. The flywheels were manufactured by RGA Investments, an arm of advanced engineering and technology group RGA Labs.

Convergent claimed the flywheels help support the local transition away from fossil fuels and towards renewable energy and also support the local grid at much less expense than the equivalent in transmission or distribution infrastructure upgrades. The company said it manages “all aspects” of development for its customers, which include utilities, grid operators and industrial entities.