A collaborative project between RheEnergise and the National Engineering Laboratory.RheEnergise are developing a technological solution where a high-density-fluid (2.5x the density of water, about the density of concrete) can be used in pumped energy-storage applications, increasing both the power and energy densities of pumped energy-storage projects. The high-density-fluid means that sites can be found in locations with lower elevations (~9,500 in the UK alone) and that civil engineering work is also reduced by 2.5x. Projects are closed loop and can therefore be located in any climate, including deserts.The project seeks to identify how ultra-high efficiencies (~96% mechanically) can be maintained with the high-density-fluid and how operational and maintenance costs can be minimised through both a breadth and depth of understanding of fluid-flow characteristics through turbo-machinery.The potential opportunity is for RheEnergise (and other UK businesses in the supply-chain) to capture a large percentage (perhaps 10%) of the total global predicted energy-storage and system-flexibility market, using a gravitational/ mechanical solution rather than solely relying on emerging battery technologies for future system-flexibility.RheEnergise has identified the need to undertake this research work to address the huge potential market for system-flexibility:Aurora-Energy-Research forecast a £6bn requirement, in the UK alone, for 13GW of new flexible assets by 2030, and Bloomberg-NEF predict a global energy-storage market worth \>$600bn by 2050\.This projects goal is to enable a 10% increase in operational and cost efficiencies that in-turn enables RheEnergise to reach its goal of ~10% global market share, meaning ~$6bn of direct benefits to the UK economy, driven by a UK innovator company.The Committee-on-Climate-Change, National-Grid, Energy-UK, IPPR and many other commentators all state that energy-storage is the enabler required to achieve a net-zero carbon energy-system.Parts of the world have already demonstrated that renewable energy plus storage is cheaper than coal, nuclear and even gas. RWE has abandoned new coal development in Germany. Off-shore wind contracts are now <£40.00/MWh in UK and France. On-shore wind and solarPV in many locations globally is contacted ~£30.00/MWh.RheEnergise's GIS analysis shows ~9,500 UK site opportunities, ~80,000 Europe (ex. Nordics), ~160,000 Africa.At an average project size of 20MW/80MWh, only 350 UK sites would be required to provide 50% of Aurora's predicted 'need' for the UK's 2030 market. The numbers of wind-power and solarPV installations seen in the the last decade shows that the construction of 350 sites in a decade is entirely achievable.