The objective of the project is to develop and demonstrate a viable energy storage method for offshore purposes by means of the flywheel energy storage system (FESS). It will lower the energy consumption of the drilling vessels by 20% at a substantially lower price compared to other energy storage solutions, thus creating a new Danish industry for energy storage. FESS is currently only being used for smaller scale onshore energy storage. However in this project, the FESS will be developed and demonstrated to meet the specific requirements of drilling vessels and vessels, to prepare for a broad maritime use of this technology. Vessels have fluctuating power demand, i.e. their engines are procured according to the max. load needed. Unfortunately, the engines are developed to be most fuel efficient at max. load despite average load aboard a drilling vessel are only 40-45%, thus making them inefficient. Increased load makes the engines operate with improved fuel efficiency. By using FESS engines can be smaller to increase their load point and charge the FESS gradually; when additional power is needed the FESS will kick in, resulting in fuel savings of app. 20%. Additionally, in case of power blackout, the FESS will be able to energize the vessel until the engines come online. The FESS will be designed to operate for a period of min. ten years regardless of the number of charging cycles to minimize costs and environmental impact. After the project, we will sell to professional +5MW vessels, resulting in a payback time for the customer of less than a year.