With deep geothermics, groundwater is directly collected at a high temperature, then re-injected at a lower temperature after the heat was captured from it. These systems can be used for district heating or energy production.
The principle is similar to open shallow geothermal systems, as groundwater is collected directly and pumped to the surface. However, due to the water temperatures at these depths, the thermal energy captured can be used without a heat pump in systems that require high temperatures, e.g. district heating or power-generating turbines. Deep geothermal systems (1,000+ metres) reach depths that require advanced drilling techniques, and the ground must generally be stimulated in order to artificially increase its hydraulic conductivity and extract more water in order to increase the system's efficiency.
Such systems are generally destined only to large-scale uses, and are not practical for individual uses; however, they can be very efficient for heating large industrial complexes or entire city districts.
Deep geothermal systems require specific geological conditions that are fairly uncommon. In Belgium, only in a few sites can water be collected at such temperatures and at reasonable depths. In Saint-Ghislain (Hainaut province), for instance, water can be collected at a temperature of 72 °C, 2,400 metres below the surface. This is the only deep geothermal system in Belgium used for district heating.