in heating costs, and 20–50 percent in cooling costs, compared to conventional systems. Geo-exchange systems also save money because they require much less maintenance. In addition to being highly reliable they are built to last for decades. Some utilities, such as Kansas City Power and Light, offer special, lower winter rates for geothermal customers, offering even more savings. Geothermal drilling risks In geothermal heating projects the underground is penetrated by trenches or drillholes. As with all underground work, projects may cause problems if the geology of the area is poorly understood. In the spring of 2007 an exploratory geothermal drilling operation was conducted to provide geothermal heat to the town hall of Staufen im Breisgau. After initially sinking a few millimeters, a process called subsidence, the city center has started to rise gradually causing considerable damage to buildings in the city center, affecting numerous historic houses including the town hall. It is hypothesized that the drilling perforated an anhydrite layer bringing high-pressure groundwater to come into contact with the anhydrite, which then began to expand. Currently no end to the rising process is in sight. Data from the TerraSAR-X radar satellite before and after the changes confirmed the localised nature of the situation: A geochemical process called anhydrite swelling has been confirmed as the cause of these uplifts. This is a transformation of the mineral anhydrite (anhydrous calcium sulphate) into gypsum (hydrous calcium sulphate). A pre-condition for this transformation is that the anhydrite is in contact with water, which is then stored in its crystalline structure. There are other sources of potential risks, i.e.: cave enlargement or worsening of stability conditions, quality or quantity degradation of groundwater resources, Specific hazard worsening in the case of landslide-prone areas, worsening of rocky mechanical characteristics, soil and water pollution (i.e. due to antifreeze additives or polluting constructive and boring material). The design defined on the base of site-specific geological, hydrogeological and environmental knowledge prevent all these potential risks. See also Annualized geothermal solar Carnot's theorem (thermodynamics) District heating Geothermal gradient deep in the earth Geothermal (geology) Geothermal power Geothermal heat pump Thermal battery References External links Energy Efficiency and Renewable Energy (EERE) - Geothermal Technologies Program Idaho National Laboratory - Geothermal Energy Oregon Institute of Technology - Geo-Heat Center Southern Methodist University - Geothermal Lab Geothermal Technologies Program at the US National Renewable Energy Lab The Canadian GeoExchange Coalition Energy conversion Heat pumps