Chimney Solar Dryer

Summary

The chimney solar dryer is a low-cost innovation to hygienically dry fruits and vegetables that is faster than traditional cabinet dryers and holds more product. The chimney solar dryer has been used in numerous countries both for individual use to preserve crops and as a way to create a value-add product for sale.

Challenge/Problem

Smallholder farmers lack access to effective and affordable drying solutions for fruits and vegetables. These crops are often harvested in high volume over a short period of time, when quality is high but prices are low. Rates of loss and waste in fresh produce can be quite high, especially in developing countries. Solar drying of fresh fruits and vegetables is a simple processing technique that adds value to crop surpluses, preserves and extends food supplies, empowers smallholders and creates rural employment. Drying provides an alternative outlet for their surplus production, both for sale and for improved family nutrition during the off season.

Solution

The chimney solar dryer is designed to provide efficient drying even in hazy or partially cloudy conditions, using inexpensive and readily available materials. The chimney of the solar dryer ensures continuous air flow around the product, thus increasing the speed of drying compared to other designs. Additionally, the solar dryer has a large heat-collection area ensuring high temperatures and rapid water removal; and a flexible design allows users to modify tray depth and size to fit consumer demands.

The Chimney Solar Dryer is a cost-effective, small-scale processing option for smallholder farmers. It can be easily modified to suit specific requirements of different products and climates and provides benefits of solar drying even in hazy or partially cloudy conditions. The Chimney Solar Dryer dries produce twice as fast as cabinet dryer designs. Materials can be purchased for less than $150; however, costs are subject to local variation. Thin items like herbs and leafy greens may dry in a few hours, while large products like whole apricots or whole bananas will require several days to dry. You can decrease drying time by removing pits, peeling the product, and/or cutting it into thin slices.

Results

- Researchers with the Horticulture Innovation Lab have used chimney solar dryers with farmers in the United States, Ghana, Nepal, Guinea, Kenya, Tanzania, Bangladesh, Thailand, Guatemala and Honduras.

- One example of a small business that started from the chimney solar dryer is a young, female entrepreneur in Guinea. The entrepreneur built the chimney solar dryer to dry pineapples. She then sold the dried pineapple slices in local market at a premium rate.

- The instructions for building the chimney solar dryer are available in a manual and in videos on the Horticulture Innovation Lab website, and users from several countries have independently built the chimney solar dryer using locally available materials.

- The chimney solar dryer protects drying products from rain and dust while drying and can speed up drying time compared to control significantly. The chimney solar dryer can dry twice as much product in half as much time compared to traditional cabinet solar dryers.

Lessons Learned/Potential for replication

In many cultures dried foods are a novelty, and that could be a last mile issue in such cultures. Incorporating instruction on how to integrate dried commodities into culinary dishes could benefit adoption of the technology.

Next Steps

This is an open-source design, and The Horticulture Innovation Lab has created a manual on our website with a detailed materials list, isometric illustrations, photos, directions for how to build, troubleshooting tips and other user support. Additionally, short videos on the website show how to build and use a chimney solar dryer. Find videos and manuals at: https://horticulture.ucdavis.edu/chimney-solar-dryer.