A new system that uses water based solar collector incorporating, storage, regeneration and generation adsorption columns has been developed. The drying chamber has been maintained at a much stable temperature and humidity for high quality drying. The quality of the dried herbs is better since many of the active ingredients remain intact after the drying process. The payback period for the system is 3.8 years. A method and an apparatus for drying heat-sensitive products, particularly one which runs by solar power. The inventive solar dryer comprises a plurality of evacuated tube solar collectors, a dehumidifier, an a drying chamber. The dehumidifier comprises at least two columns packed with adsorbents, and each column is alternately used for moisture adsorption. This invention provides a continuous dehumidification and an effective method of removing excess moisture from heat-sensitive products, e.g. medicinal herbs and the like.