A source with a low energy density, e.g. due to a small temperature difference from the surrounding environment, so it is sometimes considered waste heat. Since the conversion of one kind of energy into another is never 100%, there is always some waste heat. It is often dissipated uselessly into the atmosphere, but it can be used. For example, the interior of a car can be heated by waste heat from a running engine or a house can be heated by low potential heat from a nearby power station. Another possibility of using low potential heat is the binary cycle. Here, the thermal energy of an input medium (e.g. water from a geothermal borehole at 60 °C) is transferred to another type of medium (e.g. ammonia), which converts to steam at this temperature and can drive a turbine.