Summary There is a range of uses for groundwater and aquifers, mostly non-water supply uses, which have been termed ‘exotic’. These uses can be categorized into four distinct fields: fluid storage and waste disposal, including deep-well injection; energy conservation, including storage of fossil fuel-generated energy (as heat or pressure) and the extraction of solar energy from groundwater; subsurface in situ leaching of economic minerals; and groundwater quality management. Some details of each of these fields of application are presented to illustrate their essential multi-disciplinary nature and also the benefits that can arise from their use. Much more intensive investigation than normal is considered necessary to obtain the detailed site-specific data that any application would require. This would also have to be linked with an adequate regional monitoring system, which protects potable groundwater and other minerals. Possible applications in the United Kingdom are considered.

Groundwater and aquifers; an overview of ‘exotic’ uses

Worldwide vast experience exists, dating back to 1915, for liquid and gaseous hydrocarbons storage deep underground in geological strata/traps. Storage options include salt caverns, porous rock (depleted hydrocarbon fields or saline aquifers), abandoned mines and mined (unlined or lined) rock caverns, which offer opportunities for compressed air energy storage (CAES). Underground storage presents a number of benefits, notably very large volumes of gas (including air) stored at high pressures (up to 200 MPa), a small footprint with low environmental impact and considerable protection against external influences. CAES plants using solution-mined salt caverns have operated commercially since 1978 (Huntorf, Germany) and 1991 (McIntosh, Alabama, USA). Despite many studies, proposals and tests in most underground storage types since the 1970s, no further commercial plant was commissioned until 2019 with an ACAES plant at Goderich (Ontario, Canada), utilising a former brine cavern. The development and increasing integration of inherently intermittent renewable energy sources into the electricity grid means that CAES is once again being considered to provide rapid response, bulk energy storage, load-levelling and grid-scale support. Various CAES test types have commenced in salt caverns, tunnels and areas of abandoned mines. Options for geological storage, CAES development to date and some key considerations are briefly reviewed. 

The Geology, Historical Background, and Developments in<scp>CAES</scp>

Economic and engineering evaluations of energy-storage potential in certain USA aquifers are being conducted Particularly detailed evaluations have been made for compressed air energy storage (CAES), using off-peak power from nearby nuclear power stations In current studies, we are examining thermal energy storage and utilization prospects, using solar power or, alternatively, off-peak, low-cost nuclear power as the heat source Economic and energy-saving aspects of selected combinations of sources, storage media, and uses are ranked with respect to various selection criteria

D.H. Stewart

Papers

Energy storage in aquifers