Aspects of Solar Drying

Abstract

The oil crisis and the increasing danger of pollution of the environment compelled mankind to a renewed stock-taking of possible energy sources and reconsider the viewpoints of energy economy.

In the course of these considerations the renewable energy sources came into the focus of interest and the possibilities in solar energy have also been rediscovered.

Setting out from the incontestable advantages of solar energy there was an enthusiastic upswing at the initial stage, which was followed by a disheartened period and at present a realistic way of looking at the possibilities is existing.

The prerequisite of utilizing solar energy for drying is rentability, i.e. an acceptable payback time.

The realization of the importance of economy aspects followed by detailed analysis lead to the knowledge of the main influencing factors, their role and mechanizm. Difficulties arise from the time-dependent and diluted character of solar radiation. This involves problems requiring different means for their solution /heat Storer, auxiliary energy source, large collector surfaces, control system/ and so the investment cost are considerable.

For the economical utilization of solar energy for drying it is necessary to coordinate the drying purposes with the specific characteristic of solar radiation /e.g. small power demand; products requiring low temperature drying, fitting the peak requirements to the highest radiation period/. Several agricultural and forestry products correspond to these requirements.

The other possibility for increasing rentability is the reduction of investment costs. In this respect there are two possible ways: to use simple, cheap, plain constructions or to develop multi-purposed and integrated systems used throughout the whole year.

In any case the task has to be handled as an optimum problem and can be solved by the use of computer simulation.

Appreciating the advantages of using solar energy for drying considerable research and developing work is in progress all over the world and economical solutions have already been found. However, the period of searching for new ways has not yet come to an end.