When we think of thermal energy storage, we typically think of things that are hot. However, all we really need for thermal energy storage is a temperature differential – regardless of whether it is hotter or colder than our baseline temperature.

Keep this fact in mind for the engineering trivia question: “In a post-apocalyptic world, would you rather have a kg of room temperature water or a kg of ice?”. The answer: “Ice is preferred as we can generate energy from the temperature difference between it and the ambient air”.

Along the same lines, low temperature liquids can be used to accomplish cold energy storage (CES). Most commonly, liquid nitrogen and liquid air are used as the storage medium.

One of the world’s largest cold energy storage plants is about to come online, and it uses liquefied air to store energy. This facility is located in Manchester (United Kingdom), and will primarily store electricity generated from renewable energy by using the renewable power to chill air into a liquid. The liquid air, with a temperature of -190 degrees Celsius, is then sent to an insulated tank where it is stored until power is needed.

When power is needed, the liquid air is allowed to warm up. When it does, the liquid air expands into a gas and is able to spin a turbine to produce electricity. Based on design estimates, this plant can power around 5,000 homes for three hours.

Power storage is a key issue in the renewable energy field. This is because power sources such as solar and wind are intermittent, and we need to “smooth out” the power supplied to the electricity grid.