A developed solar system was used for dehydration some leafy medicinal plants and for storage of solar energy in water. It consisted of a flat-plate collector, a reflector, a drying unit, an auxiliary electric heater and a water tank. The solar system was tested during June to September 2009 for drying Lemon balm (Melissa officinalis L.) and peppermint (Mentha pepperita). Inlet air temperature to the dryer was higher than the ambient temperature and it could be maintained as desired using a temperature controller. Drying was taken about 8 to 10 hours to reduce the moisture contents of Melissa from 70-72 to 9% (wb) and 33 hours to reduce it from 70-72 to 17% (wb) by the hybrid dryer and natural sun drying method, respectively. Moisture content of Peppermint was reduced from 69-71% (wb) to 8-9 % (wb) in 10-12 hours by hybrid dryer and 51 hours by natural sun drying to reduce the moisture contents of it to 10% (wb). The capacity of the dryer was to dry about 16-20 kg of fresh Lemon Balm and also about 16-20 kg of fresh Peppermint per batch for each plant. The color, oil content and appearances of the products dried in the hybrid dryer were better than sun drying method.
The dryer was also occupied with an auxiliary heat source to be used whenever adverse weather conditions exist. Using the water tank, about 15-20°C can be maintained in water during the time of sun-shine. During night time,the stored head is transferred from the water to the drying air inside the solar dryer and controls the air temperature through the drying process at night.