Meeting future inertia requirements and ensuring the frequency stability of the electricity grid in a renewable energy system are key challenges resulting from the energy transition. One solution is the innovative hydraulic variable inertia flywheel, developed at Flensburg University of Applied Sciences. Its variable mass moment of inertia allows it to exchange energy with the grid while rotating at a quasi-constant speed. By connecting it to a synchronously rotating electrical machine, it provides inherent grid-forming and grid-supporting functionalities.

Within the research project T!Raum Inno!Nord-HYDRAD, flywheel demonstrators are fabricated at various scales using large-format additive manufacturing. From a research perspective, the primary advantage of this approach is the ability to build and test different geometries and sizes independently. When designing the flywheel, sustainability aspects must be considered alongside functionality. Therefore, this article aims to identify the most sustainable material for the construction of the hydraulic variable inertia flywheel, based on previous work that identified the most suitable geometry from a sustainability perspective.

A strength calculation is used to determine the required wall thicknesses and resulting material needs for various flywheel sizes. Subsequently, a design tool calculates the energy output for different materials and scales. These results are then used to determine the resulting CO₂ emissions and the carbon-specific energy density in kWh / kg CO₂ equivalent.

In addition to conventional manufacturing materials such as steel and aluminium, the three most common 3D printing filaments – acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polyethylene terephthalate glycol-modified (PETG) – are considered. While steel and aluminium possess significantly higher strength, allowing for larger dimensions, 3D printing offers the advantages of being cost-effective, readily available, and easy to implement. Due to the lower strength of 3D printing filaments, the maximum size of the flywheel is limited. Comparing these materials and manufacturing methods not only reveals the most sustainable material but also allows for conclusions on whether it is more beneficial from a sustainability perspective to utilise a few large flywheels or many small, distributed units. Furthermore, the deployment of numerous small units in the distribution network would increase grid resilience.

The results of this article regarding sustainable materials significantly influence the development of the hydraulic variable inertia flywheel, which can make a substantial contribution to stabilising future renewable electricity grids.