Sludges containing water can only be dewatered to a certain extent mechanically. Beyond this level, moisture must be expelled by means of thermal processes. In the municipal sewage treatment plant in Kandern-Hammerstein. IST Anlagenbau GmbH has operated its own development, a solar dryer for sewage sludges, since December 1994. The result reveals that about 700 - 800 kg water/m(2) ground space and year are evaporated in southern Germany. Recycling of waste hear enabled a heating of the ground plate thus doubling or tripling the drying performance. The unit operates fully automatically with a PLC control system. Although considerably more ground space is required than in comparison to an industrial drying unit, operating costs of the solar drying system are competitive, frequently even considerably lower. In the mean time, a second drying plant has been in operation since August 1997 in Iffezheim near Baden-Baden. Many improvements were made in details of design. In principle, the process can be applied for all bulk materials containing water