One of the major drawbacks of solar and wind energy is that wind and the sun do not produce enough energy on a continuous scale. It is said that wind turbines tend to be productive only when the demand for power is low (during morning and evening) and become passive by the middle of the day when the need for electricity increases. So that poses a question about energy storage and whether it could be a potential solution, ensuring we get the best out of our renewables.Energy storage could ensure stable power supply during the day as well as at night.
While batteries are suitable for small-scale energy storage, historically, pumped hydro has been employed for large-scale energy storage. However, batteries used for energy storage are expensive and not sustainable in their current forms. This could be down to the fact that most types of batteries require the use of rare metals. Similarly, pumped hydro technology is limited by certain geographical constraints and its need for large amount of water, thus not making yhe process feasible under various circumstances.
In an attempt to solve all the existing problems with energy storage, Highview Power Storage, a company based in UK, has developed a facility that uses liquefied air or liquid nitrogen as the storage medium. According to the Institution of mechanical engineers, liquid air can compete with hydrogen and batteries for storing excess energy generated from renewable resources.
Liquid Air Batteries
The liquid air storage technology was first developed by Peter Dearman, a garage inventor from Hertfordshire to power vehicles. This process operates by making use of energy from a renewable source such as wind turbines during peak production times for freezing air that is free of water vapor and carbon dioxide. The air is frozen down to -154.4°C (-310°F), to the point at which it is converted into liquid. The liquid air is kept in a giant vacuum flask until it is required for use. When the demand for electricity increases, the liquid is warmed to ambient temperature. As it vaporizes, the expanding gas is used for driving an electricity-generating turbine or idle wind turbine blades without the need for combustion.
Liquid air generally has a high expansion ratio between its liquid and gaseous states, thus expanding around 700 times upon re-gasification. However, a cryogenic engine depends on phase-change and expansion within a confined region, e.g. turbine or engine cylinder. Highview Power Storage has now developed a fully operational 2.5MWh, 300kW, pilot plant, which is partly-funded by the UK Government's Department of Energy and Climate Change and linked to the UK's national grid, complying with all the necessary regulations and inspections like any other commercial generator. The system has the potential to be scaled up to 100MWs/GWhs of storage like a medium-scale pumped hydro. Also, liquid air can be easily stored in the low-pressure tanks and is hundred times denser than water.
Benefits of Liquid Air Batteries
Some of the key benefits of liquid air batteries include the following:
- Storage of liquid air is at low pressure and hence there is no risk of fuel combustion
- It does not require scarce materials
- It has very fast re-fuelling times
- Liquid air is a superabundant and inexpensive feedstock
- Cryogenic liquid production and its supply chain is already mature
- Liquid air has energy density competitive with that of other low-carbon technologies
- It makes use of waste heat to warm liquid air
- It can be up to 70% efficient in large scale. Discharge of energy is extremely fast when provided with sufficient heat.
Future of Liquid Air Batteries
Although power grids are a type of batteries that can store energy for some amount of time and redistribute it when required, large-scale local storage system like the one developed by Dearman would help level out the difference between peak production and peak demand. Cryogenic liquids are widely employed in industrial processes already, and their application as energy vectors is just the beginning. However, several companies in the UK have started securing strategic partnerships across the world for providing liquid air energy solutions.
According to Dr Tim Fox, Head of energy & environment at the Institution of mechanical engineers states that new solutions are required to create and store green energy for use in vehicles, homes and factories. Liquid nitrogen and liquid air are interesting alternatives that should be explored for energy storage. This technology can address most of the challenges involved in commonly used energy storage methods and is affordable and scalable. However, the scale of the industry supporting liquid air would be larger than the industrial gases sector, and hence like all other emerging renewable or low-carbon technologies, this also requires support from the government for shifting it from pilot plant to commercial plant.
Sources and Further Reading