Solar energy for herb drying : A thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of Canterbury [Lincoln College], Christchurch, New Zealand

Abstract

A study was undertaken to establish the dimensional and operational parameters of a farm-sized herb crop drier utilising forced convection and solar energy. To facilitate the study, a solar herb drier was built at Lincoln College. Information on the design, construction, testing, and economic viability of the drier is presented herein. During testing of the drier the efficiency of the drying process was studied, as well as air flow - rates, time requirements for drying, and drying characteristics of available herbs. The solar drier was designed to compete with conventional herb driers using oil fuel for their air heaters. Thus the design has attempted to achieve low cost, low maintenance requirements, simplicity of construction, while maintaining good efficiency. Operation of the solar drier has yielded interesting and useful results, which confirm that the design was successful. The efficiency of the drier is acceptable, varying between 50% and 60%. Total running costs, comprising electricity and labour costs, are in the range of $0.70 to $1.25 per kilogram of finished dried herbs. These results indicate the suitability of the solar herb drier for use on small scale herb farms, growing up to 0.40 ha of herbs. It would compete with alternative equipment in view of the current market price of between $6 and $16 per kg of dried herbs Good quality of the dried product is maintained in the presence of moderate air temperatures and high rates of air flow.· The herbs under these conditions, retain most of their volatile oil content, plus their original greenish colour. These factors have an important effect on the sale price of the dried herbs.