Within the national energy research and development programme the Swedish Council for Building Research is responsible for the programme of Energy use for Building a excl. industrial development support, which is administrated by the National Swedish Board for Technical Development. The Council is also responsible for energy prototype and demonstration activities in existing buildings and for experimental building activities. In its application for appropriations for the period of 1981–1984 the Council will present a proposal to a plan for its energy related activities during the current three-year period. The council has created a number of working-groups in order to work out the future action-programme, estimate the potential of different development strategies and propose activities as research, experiments and demonstration plants. This paper presented by one of these groups, deals with storage of waste heat and solar energy in soil, rocks, surface, and ground water and also bottom sediments in lakes and bays. The energy storage of solar heat is of great importance because the -energy has to be stored over a period of more than half a year. The energy storage is as a principle divided into

  1. Active systems, which are charged to a higher temperature range by a gaseous or liquid heat transfer medium and

  2. Passive systems, which are charged in a natural way by rainfall, atmosphere or solar energy during the summer.

The active systems consist of stores in the underground or near the surface. the passive systems of stores in the surface, in lakes or in the ground water. Development potentials, ecological aspects, legal aspects and development resources are discussed.

SUMMARY

Description of subject area The subsurface storage of energy can be divided up into so-called active systems, where the storage facility is charged by solar collectors, heat pumps or waste heat, and passive systems, which are only heated by natural means.

Active systems

Theoretical calculations and small-scale pilot projects indicate that there are technical and economic grounds for storing heat under the ground. Storage on a relatively large scale is necessary with regard to heat loss, a factor which means that active energy storage systems are mainly of interest in connection with district heating and heat distribution centres serving groups of buildings. The field can be, divided into deep subsurface storage, aquifer storage and storage in water-filled rock caverns.

Deep subsurface storage

Deep subsurface storage is understood to comprise energy storage systems where charging and energy extraction occur via a closed circulation system in a vertical cavity. By utilizing thick layers of clay or rock from a depth of approx. 5 m down to about 200 m, heat can be stored on a seasonal basis in a fairly clearly defined volume of soil/rock. This storage technique is in principle dependent on the total absence of groundwater flows. Low storage temperatures ranging from between 10 to 15°C lead to a reduction of less favourable side effects in the facility such as heat convection and groundwater movements.

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