Why compressed air could keep the lights on

Ewan Murray | 22 Jan 2016 | Comments

Although it can all sound like doom and gloom, there are a number of exciting, breakthrough technologies that could help address the UK's energy problem.

Energy supply in the UK faces a problem. It has been discussed at length by leading energy experts, yet I feel it can be summed up simply:

“With diminishing baseload generation in the UK, combined with the impact of the rapid growth in intermittent generation (i.e. offshore wind), the household peak demands cannot be met with our current power infrastructure.”

There are revolutionary techniques being developed which will completely change the way in which energy is stored; something which is becoming increasingly important in securing supply through intermittent generation.

Unfortunately, most low carbon energy storage technologies currently lack the investment needed to make them commercially viable on a large scale, and would benefit greatly from a similar level of support that has been given to wind power in the last few years. But despite the lack of investment, some of these low carbon breakthrough technologies are almost ready.

Compressed air energy storage (CAES) is a technique used to store energy using compressed air for later use.

The first of its kind – and still the world’s largest – E.ON’s Huntorf power station in Germany was commissioned in 1978. The 321megawatt (MW) plant uses two 150,000m³ salt caverns to store compressed air. Two projects in development, Project ADELE in Germany and another in Larne, Northern Ireland, will also use salt caverns as a means of storage. RWE’s ADELE will have a capacity of 90MW and is due for completion in 2019. Larne will be larger, at approx. 300MW, which is being developed by Gaelectric.

The CAES process:

  • Atmospheric air pressure at sea level is defined as just over one bar. For storage, air is generally pressurised to around 45-70 bar (although higher pressures can be achieved depending on the structural integrity and depth of the storage volume) and is typically stored in underground caverns
  • These underground caverns are usually solution mined in the salt layer using freshwater under a blanket of N2 gas to extract a brine solution. We discussed salt caverns in a recent piece on carbon capture and storage
  • When required, the compressed air is heated and expanded in a turbine which drives a generator to produce electricity.

On a larger scale the heat energy associated with compressing air must be managed properly. There are examples where this has been done on a small scale (such as in transport) and there are a number of other ways of doing this in mediums that can store heat (such as molten salts, gravel pits, concrete, oil, or water). The challenge at a larger scale is to store the heat safely with minimal losses.

Atkins is currently working alongside leading salt storage specialists DEEP on several gas storage projects in the UK. We see standalone energy storage and grid integrated energy storage – where primary energy goes through energy storage before being converted to electricity for supply to the national grid – as a crucial part of the future global energy mix.

With the recent Paris (COP21) commitment from 195 countries to meet a global temperature rise of less than 2˚C it is very likely that CAES will play a role in maximising renewable energy efficiencies and meeting peak energy demands.

In addition, different divisions within Atkins is currently working on first-of-a-kind offshore floating wind platforms. It is possible that an element of energy storage could be built into these structures to improve individual wind turbine generator capacity factors. One solution is for direct conversion of the energy generated by the wind turbine to compressed air which is then stored under the sea in “energy bags” which could provide some element of ballast to the structure. Trials of this technique are already being carried out in Toronto, Canada at a 5MW capacity.

It is clear there is no front runner in energy storage, and a combination of innovative solutions (including thermal, electrical and mechanical) will help solve the instability in the grid. This makes it a fascinating time to be involved in such an evolving energy market and the Atkins energy storage team intends to be at the forefront of the latest energy storage projects.