Solar Crop Drying

1
Solar Crop Drying

• Solar Energy Applications
• EnvS 116
• Asim Zia
• Department of Environmental Studies
• San Jose State University

2
Overview

• What is Crop Drying?
• Problems with traditional open sun drying
• What is solar drying?
• Classification of Dryers
• Typical Solar Dryer Designs
• Operational parameters affecting the performance
  of solar dryers
• Assumptions in the performance analysis
• Unit Cost of Solar Drying for Various Crops
• Efficiency and Cost relationships
• Financial performance of solar dryers versus open
  sun dryers
• Conclusions

3
What is Crop Drying?

• Crop Drying is a dual process of
• heat transfer to the crop from the heating source
  and
• mass transfer of moisture from the interior of
  the crop to its surface and from the surface to
  the surrounding air
• Drying is practiced to enhance the storage life,
  to minimize losses during storage, and to reduce
  transportation costs of agricultural products

4
Problems with traditional open sun drying

• High crop losses ensue from inadequate drying,
• fungal attacks,
• insects, birds and rodents encroachment,
• unexpected down pour of rain and other weathering
  effects

5
What is solar drying?

• In solar drying, solar-energy is used as either
  the sole source of the required heat or as a
  supplemental source.
• The air flow can be generated by either natural
  or forced-convection.
• The heating procedure could involve the passage
  of preheated air through the product or by
  directly exposing the product to solar radiation
  or a combination of both

6
Classification of Dryers
7
Typical Solar Dryer Designs
8
Operational parameters affecting the performance
of solar dryers

• Drying air characteristics (such as drying air
  temperature, humidity and air fow rate)
• Crop variables (crop throughput, initial and
  final moisture contents, crop size and size
  distribution) and
• Dimensional variables (width, length, height or
  diameter of the dryer, number of passes and dryer
  configuration).

9
Assumptions in the performance analysis
10
Unit Cost of Solar Drying for Various Crops
11
Efficiency and Cost relationships
12
Financial performance of solar dryers versus open
sun dryers
13
Effect of f1 (fraction of dried product lost in
open sun drying) on estimated benefits
14
Conclusions

• Solar drying of agricultural products appears to
  be financially quite attractive for cash crops
  (such as tea, cardamom, etc.) and it may even be
  possible to justify the use of high cost solar
  drying systems in their case. However, for drying
  highly perishable products such as vegetables and
  fruits, it is extremely important to develop low
  cost solar drying system preferably using local
  materials and skills.
• Financial performance analysis is limited due to
  the key parametric assumptions