Evaluation of liquid air as an energy storage alternative

Sammanfattning: As renewable, intermittent energy sources are expected to increasingly replace fossil based energy, energy storage technologies are crucially important in achieving the goal of fossil free energy, a cornerstone of sustainable development. Liquid air energy storage (LAES) is a novel technology that liquefies air when excess electricity is available. The liquid air is stored and, when electricity is needed, expanded in a turbine to generate electricity. The purpose of the project is to present the round trip efficiency of LAES, discuss how it can be improved and how it depends on relevant parameters and to evaluate LAES compared to other energy storage technologies. A literary review of existing energy storage methods and LAES research is presented. The efficiency is calculated using a model of a combined Linde (liquefaction) and Rankine (discharge) cycle built in Excel. We found that the efficiency of LAES is 21,6% without heat and cold recycle and above 50% with more than 60% recycle. Access to waste heat and cold can further increase the efficiency. A heat pump affects the efficiency very little, but is useful to protect the turbines from low working temperatures that can damage them. The biggest advantage of LAES is its high energy density, comparable to batteries and chemical energy storage. It is much higher than pumped hydro and compressed air energy storage (CAES). No toxic materials are used and it has reasonably cheap and long lasting components. It uses air, which is free as an energy carrier. The biggest disadvantage of LAES is its low round trip efficiency, probably under 50%, which is much lower than that of batteries and pumped hydro. It is similar to CAES and other chemical storage. LAES is only practical on a relatively large scale. Also, concentration of oxygen and cold working temperatures pose some safety risks.