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Dehytray solar-powered food dryer drying fruit Klein Ileleji
SOLAR DRYER: The Dehytray developed at Purdue and pictured on the left was tested on this organic fruit farm in California.

Solar-powered crop drying may work on small scale

Purdue research leads to a unique solution offered by a startup company.

In developing countries in Africa and Asia, it’s common to see farmers drying their crops on the side of the road. These farmers use the heat from the sun to dry everything from grains and vegetables to seafood and fruit. This method of drying leaves crops susceptible to insects, rodents, strong winds and rain, which can drastically damage the crop. Although this problem is common for farmers in underdeveloped countries, it’s still a problem farmers face in the U.S., too.  

Farmers in the U.S. deal with postharvest problems that waste not only the crop but also the money and energy used to produce the crop. Solar energy dryers may offer a solution for small growers or specialty crop growers where artificial electric dryers aren’t feasible.  

Klein Ileleji, a Purdue University Extension ag engineer, created a solar-powered crop-drying device. The device was developed as part of a Feed the Future Innovation Lab project on postharvest handling and food processing led by Purdue University. It’s funded by the U.S. Agency for International Development, established by President John F. Kennedy in 1961 and more commonly known as USAID.

The Dehytray is licensed and trademarked by a Purdue-affiliated startup company, JUA Technologies International. It received a 2019 award for one of the best innovations in engineering and technology for agriculture from the American Society of Agricultural and Biological Engineers.  

Practical solar drying 

As of now, there are very few other solar dryer devices that can be purchased commercially that meet the needs of small growers. This solar dryer can be used on grains but is more economical for fruits, vegetables, herbs, spices, pellets and ornamental plants. The product was designed to make it easy for an average small-scale farmer to use it.  

Ileleji says he wanted to make the solar dryer user-friendly because he appreciates how Apple products are designed in that way. “IPhones these days don’t come with a manual; you just buy one and use it, and that is what I was trying to achieve myself,” he says. 

To get the solar dryer designed as a commercial product for manufacturing, Ileleji worked with Heeju Kim, a visiting research scholar at Purdue University’s School of Design. 

The Dehytray is just under 3 feet long, and according to the JUA Technologies website, it can save users almost a day of drying time when compared to other dryers. The solar dryer can double the ambient temperature by absorbing heat radiated off the walls of the drying trays. The weather-resistant cover can withstand sudden temperatures as high as 176 degrees F. 

The device is sold with a hygrometer that is used to determine the water activity of the product. This measurement shows the potential growth of mold or bacteria by using the free unbound water of the product as well as indicating whether the product is appropriately dried for storage.

The relative humidity of the air in the bag with a handful of the dried product, or the equilibrium relative humidity, should be below 65% for proper storage to inhibit growth of mold. This measurement allows the user to know exactly when the crop is sufficiently dried and ready for storage. 

Alex Dayton Waltherred apples in a tree against blue sky


DRY AND PRESERVE: Food products made of apples could possibly be dried using solar heat with an invention offered by a startup company.

When it comes to drying fruits and vegetables, several methods can be used — some of which are vastly different from how grain is dried. Fresh produce is often dried for ease in transportation and to increase the shelf life.

Diana Ramirez, a Purdue graduate research assistant, says the Dehytray increases shelf life while also maintaining nutritional value. Ramirez tested the prototype on produce such as tomatoes and garlic. “The Dehytray can increase the shelf life by a year or more,” she says.

Electric dehydrators on the market give the same result as the solar dryer, just with a different process. Electric dehydrators, as the name implies, use only electricity to dry the product. Most of these devices have a timer built in rather than the hygrometer in the Dehytray that tells when the product is appropriately dried.  

Oven drying is commonly used for smaller quantities and for individuals living in an area where they can’t depend upon the sun. Although this is considered a safe method for drying, the end product tends to be more brittle and less flavorful. However, this method is affordable because it doesn’t require the consumer to make an additional purchase.  

Cost-effectiveness  

In comparison to artificial dryers such as continuous-flow dryers, the Dehytray uses solar energy rather than fossil fuels that increase energy costs dramatically. The cost and capacity of a continuous-flow dryer is much higher due to the amount of energy that is needed to keep air flowing through the products. 

To put this in perspective, the Dehytray can hold just over 11 pounds of grain, while grain dryers for small and medium-size farms hold well over a ton. However, these devices are used by large-scale growers, making them more cost-effective in developed countries in relation to the volume of crops being produced. 

The Dehytray is intended for small growers in developing countries and small growers of specialty crops or gardens in both developing and developed countries. The Dehytray is commercially available for $124.90 through JUA Technologies International for customers in North America, Japan, Australia and Singapore, and at a lower price for customers in developing countries.   

A small-scale grower who produces products for farmers markets may be more inclined to use a solar dryer like the Dehytray because of the ease of use and cost-effectiveness. Making the right choice is crucial for farmers, Ileleji says. “Postharvest issues are one of the most fundamental issues that farmers face,” he says. 

Learn more about solar drying and the Dehytray at juatechnology.com.

Walther is a senior in ag communication at Purdue University.

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