Compressed Air Energy Storage (CAES) stores energy in the form of compressed air in a deep underground geological vessel or reservoir.
During off-peak hours, electricity from the grid powers compressors that drive air into the underground storage vessel. When demand increases, the air is released to the surface and heated with clean burning natural gas to expand its volume and velocity. The air-gas mixture is used to drive a specialised combustion turbine that can generate up to 300MW of power. Because off-peak electricity rather than gas is used to compress the air, a CAES plant uses less than half the amount of natural gas required by a conventional combustion turbine.
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Although CAES facilities have been operating in Germany since 1978 and in the US since 1991, the technology has not been in widespread use. Now a number of converging factors in electricity markets are creating new value drivers for CAES, making it a commercially viable storage technology. These include high penetration of intermittent renewables such as wind, the requirement for greater flexibility in power systems and the need to reduce dependence on generation from fossil fuels.
A particular focus of Gaelectric Energy Storage (GES) is a CAES project in Larne, Northern Ireland, which has the potential for a CAES plant of between 140MW and 300MW. GES has conducted major studies with world leading advisors in the field - the first studies of their kind to comprehensively evaluate the potential for CAES in Ireland. This work, coupled with extensive energy experience, has provided GES with a broad range of skills encompassing a unique understanding of the geological, plant, system operation and market aspects of CAES.
System Management involves balancing the generation portfolio and the end user demand on a minute by minute basis. Because of the generation resource some generators are limited to when they can provide power namely wind, solar and tidal. This creates imbalances that need to be effectively managed so the end user receives a constant uninterrupted supply of energy.
By using this excess energy to run a compression unit which compresses fresh air and securely stored underground, we can make sure that most of the renewable energy generated can be used – if not immediately, then at a time when there is increased demand, or when renewable resources are experiencing periods of low production.
Storing fresh air in salt caverns is a proven, reliable and safe method of ensuring that excess energy is not wasted.
This fresh air is stored in caverns deep underground within geological salt deposits up to one kilometre beneath the ground.
The Project Team is currently exploring whether or not suitable salt deposits are available in East Antrim to create these caverns.
GES studies have confirmed that CAES can provide many benefits to a power system:
CAES can mitigate the problems caused by the variability and unpredictability of wind generation by providing the system operator with means of balancing intermittent wind power. The reduced risk of wind curtailment and increased predictability that CAES brings to the system has the potential to reduce commercial risk for renewable projects. The combination of wind generation with CAES in a portfolio increases the overall value of wind power and delivers a ‘firm’ form of wind generation to the market and end-users.
Because compression and combustion are separate processes in CAES, during generation it produces about one third of the CO2 that a similar sized conventional fossil fuel plant produces. Perhaps more importantly, the support for renewables, the reduced reliance on thermal generation and the increased overall efficiency that CAES provides results in a system-wide reduction of carbon emissions.
This is a crucial factor for any energy system and will become increasingly important. CAES contributes to security of supply of fuel and power via its support for indigenous renewable energy and the reduced reliance on thermal plants, allowing a greater level of management of fossil fuel consumption.
All these benefits result in lower costs to a power system with high renewable penetration levels, providing a potential for lower prices for the consumer.