Aquifer thermal energy storage (ATES) systems provide a method of improving the performance of more commonly installed mono-direction groundwater heating and cooling systems. Rather than using the prevailing temperature of the abstracted groundwater, ATES systems are bidirectional, therefore allowing for the interseasonal storage of low- and higher-temperature energy. This paper provides a theoretical base for ATES and an empirical review of the performance of a typical system installed in an office building in the Netherlands. This research was carried out by engineering consultancies in the UK and the Netherlands, and a UK university. The geology and hydrogeological conditions under focus can be briefly described as a confined saturated medium sand aquifer covered by horizons of clay and fine sand. A design simulation using HSTWin, a modified version of the software package HST3D, is compared against operational data collected over a 12-month period. These data were collected following 5 years of operation. The main conclusion from the case study is that there is good agreement between the HSTWin simulation and operational findings. Furthermore, it can be inferred that active ground thermal storage strategies can offer improvements over conventional ground source energy systems.

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The potential for the exploration and exploitation of geothermal energy for greenhouses in Franekeradeel in the north of the Netherlands has been investigated. Available borehole and seismic data have been used for the evaluation of the subsurface. These data show that the Slochteren Formation sandstone reservoirs are very likely present at a depth of ca 3,000 m. These reservoirs are deemed to be suitable for the production of hot water. From interpreted 2D seismic lines could be inferred that the Slochteren Formation is around 200 m thick at the proposed location. Based on the local geothermal gradient, the temperature at the top is estimated to be around 100 ºC. At the surface location a fault zone is present in the subsurface complicating the siting of the injection and production wells. Towards the northeast the proposed reservoir is seemingly less faulted. A minimum transmissivity of 11 Dm is expected, based on the measured porosity in nearby boreholes and porositypermeability relationships in the surrounding area. A potential flow rate of 160 m 3 /h is hence inferred, leading to a thermal capacity of 11 MW t which can be delivered with one doublet. Different well configurations were studied. The conclusion is that deviated wells from the edge of the surface location towards the northeast carry the lowest risk at still acceptable costs. From financial analyses taking different options into account, it was concluded that geothermal energy can deliver significant amounts of renewable energy for heating of greenhouses. In the optimum situation, the cost price of heat amounts to 6,20 Euro/GJ delivering annual 202 TJ of energy. This price is below the current price (January 2008) of natural gas at 0,20 Euro/m 3 .

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