Analysis of power supply using wave- and wind energy with offshore energystorage : A case study for Fosnavåg

This study investigates the potential of supplying Fosnavåg with renewable energy production from offshore energy sources and storage systems. The energy system under consideration consists of wave power, offshore wind power, and, finally, energy storage based on the Storing Energy in the Sea (StEnSea) concept. The aim of the study is to evaluate the technical feasibility, environmental impact, and self-sufficiency level of the proposed energy system. Global climate change and increasing demands to reduce the use of fossil energy sources are the driving forces behind this study. To meet the goal of the Paris Agreement, a transition to sustainable energy sources is necessary, with electrification and offshore solutions being of particular interest. Fosnavåg offers favourable conditions for such solutions due to its proximity to sea and local energy demand. To evaluate the system´s efficiency, three scenarios are analysed: a system with only wave power, one with only wind power, and an integrated system combining both wave and wind power. The goal is to identify which scenario can best ensure a stable and sustainable energy supply. The study assesses the technical feasibility of the different energy sources in terms of self-sufficiency, ERoEI (Energy Returned on Energy Invested) and climate impact per delivered kilowatt-hour. ERoEI is the ratio between the energy produced during an energy source's lifespan and the energy required to produce, maintain and to decommission said energy source. The results show that wave power alone has production fluctuations, resulting in periods of low self-sufficiency. Wind power offers more stable production, and with higher installed capacity and adequate storage, it can achieve nearly 100 % self-sufficiency. The hybrid solution shows the most favourable combination of stability and efficiency, achieving 100 % self-sufficiency with 233 storage units. The system´s energy efficiency is further analysed through ERoEI. The study shows that using storage units reduces the ERoEI value. A 750 kW wind turbine combined with 287 storage units reaches an ERoEI of 1,55, which is below recommended levels for long-term sustainability. However, the hybrid solution improves the value to approximately 2,2 by reducing the need for storage units to 233 and increasing self-sufficiency to 100 %. A completely self-sufficient hybrid system had a climate footprint of 207 g CO2e/kWh. For the hybrid energy system, climate impact increases with the number of storage units. Achieving high self-sufficiency requires many storage units, which reduces the system´s ERoEI and increases its carbon footprint. Therefore, a balance between self-sufficiency, ERoEI and climate impact must be considered when selecting an energy system. The study concludes that a combined system of wave and wind power, along with storage using StEnSea technology, is the most effective for Fosnavåg in terms of self-sufficiency, energy efficiency and environmental impact.