The disparity between energy production and demand has led to increased research into the use of aquifers for the long-term, large-scale storage of thermal energy. Currently, there are several field experiments and feasibility studies under way in which the technical, economic, and environmental aspects of aquifer storage are being researched. The present paper surveys the recent theoretical efforts in aquifer storage research and the impact their results may have on these field projects. Major work is highlighted according to three categories:
semianalytic studies,
numerical modeling studies, and
site-specific studies.
The need for energy storage arises from the disparity between energy production and demand. The development of viable storage methods will play a significant role in our ability to implement alternative energy technologies and use what is now waste heat. The ability to provide heat at night and during inclement weather is a key factor in the development of solar energy. Conversely, winter cold, in the form of melted snow or water cooled to winter air temperatures, can be used as a coolant or for air-conditioning. Practical storage systems would also allow us to capture the heat that occurs as a by-product of industrial processes and power production. Industrial plants and electric utilities generate tremendous amounts of waste heat, which is usually dissipated through an expensive network of cooling towers or ponds to avoid thermal pollution. Because periods of heat demand do not generally coincide with electricity generation or industrial production, a viable storage method is essential if this heat is to be used. Such a method would not only provide for the use of what is now waste heat, but would significantly decrease the necessary investment in cooling and backup heating systems. In recent years, aquifers have been studied as a very promising means for the long-term, large-scale storage of thermal energy. Aquifers are porous underground formations which contain and conduct water. Confined aquifers are bounded above and below by impermeable clay layers and are saturated by water under pressure. They are physically well suited to thermal energy storage because of their low heat conductivities, large volumetric capacities (on the order of 109m3), and their ability to contain water under high pressures. Aquifers are also attractive storage sites because of their widespread availability. Aquifer storage is not a new concept. Over the last few decades aquifers have been used to store fresh water, oil products, natural gas, and liquid wastes. However, it has only been in recent years that their use for thermal energy has been suggested. Initial studies were conducted by Rabbimov, Umarov, and Zakhidov (1971), Meyer and Todd (1972), Kazmann (1971), and Hausz (1974). A good source of information about more recent work is the proceedings of the Thermal Energy Storage in Aquifers Workshop (Berkeley, 1978). Current research and development activities are reviewed in the quarterly ATES Newsletter prepared by Lawrence Berkeley Laboratory. Recent work includes field experiments at Mobile, Alabama (USA), Gaud (Fance), Bonnaud (France), College Station (USA).
