Aiming to comply with the Paris Agreement, the reduction of Europe’s GHG emissions in the energy sector is a must. Due to the intermittency of renewable sources, energy storage technologies are essential to this plan. Offshore Low Head Pumped Hydro Storage (LH PHS) is presented as an alternative to partly solve this problem. Considering that its infrastructure entails a reservoir of a 5km diameter ring in the middle of the sea and needs millions of tonnes of concrete, sand, granite and steel among other materials for its construction; environmental concerns arouse, which this report aims to address.
Information from the Alpheus project about the engineering requirements for an offshore LH PHS plant is used, following ISO 14044 Life Cycle Assessment (LCA) methodology. In this study, the construction, maintenance and operation of an offshore LH PHS plant are assessed, focusing on Global Warming Potential (GWP), Water Use Depletion Potential (WUDP) and Abiotic Depletion Potential for Elements (ADP-E). This is studied with and without the input of electricity, sourcing it from wind or from the Dutch grid mix. Moreover, these results are compared with Lithium iron phosphate (LFP) Batteries and for Wind-Green Hydrogen.
For the construction, operation and maintenance of the LH PHS plant, it is estimated that the emissions would reach 2.8Mt of CO2-eq, 601 million m3 of water and 140.2t of Sb-eq. These emissions are mainly shared between civil and electromechanical infrastructure, the former has more relevance for GWP with almost 56% of the emissions whereas the latter reaches 69% for WUDP and 98% for ADP-E. When electricity is incorporated into the equation and these emissions are translated per kWh, emissions from the generation of electricity exceed 2.4, 5.6 and 1.8 times those emissions from the infrastructure for GWP, WUDP and ADP-E. When comparing LH PHS with other technologies using wind as the only source of electricity production, LFP Batteries outperform LH PHS most of the time for GWP and WUDP, whereas LFP are consistently the worst performer for ADP-E. LH PHS always performs better than Green Hydrogen in all three impact categories.
If emissions reductions are to be achieved in the LH PHS case, the focus should be put on the electricity side: improving the efficiency of the plant, storing only clean energy and improving the performance of renewables. Finally, there are other considerations to LH PHS implementation that should be taken into account that are not assessed in this report. The use of materials and their circularity must be considered, as well as the social ramifications of projects like PHS and mining materials for Li-ion Batteries. Furthermore, impacts on biodiversity must be addressed and its damages should not only be minimized but restored or even improved.