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From drying herbs out in the open to efficient solar dryer


Vietnamese family business Vietroselle dries herbs for the pharmaceutical industry and tea in the open air. ‘This drying process can be optimized’, the owners thought. For example by using a solar dryer. Yet how do you get from idea to realisation? Energy expert Wil Nuijen (71) offered the solution.

During an advisory mission to Vietnam, Wil Nuijen advised a company in Peru on the most efficient method drying of lucuma, a fruit sold in powder form as a natural sweetener. He designed a solar dryer at scale level that works very efficiently and is built with relatively few resources. "I bought a small greenhouse at a supermarket in the Netherlands. I added a thermostat, an old computer fan and a solar panel. Within an hour the miniature dryer was up and running. Fourteen days long we dried all sorts of fruit in it. On average, this went two times faster than drying things out in the open."

"On average, drying in the greenhouse went two times faster than drying things out in the open."


Higher quality

Increasing efficiency, delivering a better product and hence staying ahead of competitors, was also the wish of Vietroselle. Wil: "At nightfall all herbs had to be covered with sails by an entire team. Same story when there was a chance of rain." With input from the entrepreneur, Wil started work on various greenhouse dryer designs. The design that he devised in South America stood out above all: a relatively simple and inexpensive solar dryer with a metal frame, covered with plastic foil, fans and all necessary equipment for taking measurements. "A complicating factor were the hurricanes that can occur in Vietnam from September to December. Once stripped of plastic foil – there are no herbs to dry during this season anyways – the bare frame can easily survive such a whirlwind.”

Sharing knowledge

Wil: "In a solar dryer, herbs dry much faster. In addition, you prevent pollution by dust, insects and other animals, which ensures a better product. I have calculated that Vietroselle will earn back their investment within three years. The staff has to work less over time because of this system and therefore applauds the change." Hoêng Lê Xuân Quý, deputy director of Vietroselle, is also enthusiastic: "Wil shared a lot of knowledge about solar drying with us. I am convinced that we can apply the result of this project to our daily production. After the departure of Wil, we discussed with greenhouses suppliers in Vietnam and found that the metal frame that they stock is not suitable. I was about to have a local blacksmith make the frame when a friend introduced me to the director of HCMC Agricultural High-Tech Park. He has an organisation in his network that tries to save energy using the same method. We are currently working with them on our very first solar dryer."

"Replacing the sprinklers in the fields with drip irrigation saves a lot of water."

Valuable advice

In addition, Wil was able to give valuable advice that saves a lot of electricity and water. "Replace the sprinklers in the fields with drip irrigation, which saves a lot of water. In addition, no water pumping is required, saving a lot of energy. Also, the spray dryer that the company uses will be 30% more efficient with good insulation and pre-heating of the incoming air through heat exchange with the (hot) outgoing air. "

Vietroselle will soon have a solar dryer. However, they are not the only ones who will benefit from this system. Wil shared his design with other PUM experts. Currently, the design is making its way with these experts to entrepreneurs in Africa and Armenia.