Novel technology with lenses makes greenhouses more efficient

Temperature and lighting conditions in greenhouses need to be as uniform as possible for crops to prosper. For this reason, commercial greenhouse operators generally have to spend a great deal of money on heating, climate control, and shadowing.

The Dutch company Technokas has developed a solution: their Daylight Greenhouse not only consumes less resources than a traditional greenhouse—but it harvests energy as well. The technology also eliminates the need for an additional shading system.

The roof of the Daylight Greenhouse offers an alternative to other systems that protect greenhouses from the sun. It collects direct sunlight in the Plexiglas Fresnel lenses, leaving the interior of the greenhouse bathed in uniform, diffuse light, which has a positive effect on plant growth. Source: Technokas 

“Conventional greenhouses cannot utilize the entire radiation energy of the sun. A significant portion of the provided energy is lost,” says Hans van Tilborgh, one of the three managing directors of Technokas, which has been planning and implementing greenhouse construction projects, climate control systems, and business facilities in the Netherlands for 26 years.

Experts know only a portion of the sun light is used by the plants to grow. “The first thing we thus asked ourselves was, ‘How do we make use of the excess energy that a greenhouse absorbs but cannot otherwise utilize?’” Van Tilborgh recalls. The solution? A canopy that collects the direct sunlight and converts it to energy. The diffuse part of the light passes through the roofing and is made available for good plant growth. The Daylight Greenhouse idea was born.

Harvesting energy
More than a decade was required for the engineers at Technokas to develop the initial idea into series-production readiness. A unique roof construction consisting of well-insulated, double-glazed panels with embedded Fresnel lenses is the heart of the new generation of greenhouses. The lenses focus the sunlight onto a collector mounted on a 2-axis sun tracker, which in turn converts the light energy to thermal energy. “The concept wouldn’t work without the interaction between the various components,” Van Tilborgh explains. “The harvested energy in terms of hot water is then stored and used for heating during night hours or winter months.”

A roofing panel measures roughly 2,60 x 1,67 meters and consists of 16 lens panels. Each of these panels contains countless lines of small Fresnel lenses made of Plexiglas. Source: Technokas 

In addition to the development of a movable solar collector that tracks the movement of the sun, another technical challenge was the design of the lenses, Van Tilborgh recalls. “The lens material had to be able to collect and focus the direct sunlight, without absorbing diffuse sunlight which is required by the plants.” After testing a few different materials, the clear choice was acrylic, particularly Plexiglas Solar. Injection-molded lenses made from Plexiglas are manufactured by the plastics specialists at Pekago Covering Technology. “We decided on Plexiglas because it transmits light extremely well and offers long-term stability—especially compared to other plastics,” Van Tilborgh explains. Plexiglas Solar is a specialty molding compound that has been modified to transmit the wavelengths of light that plants need for their growth, while at the same time offering even higher UV stability. “That means it will retain its high light transmittance for decades,” notes Peter Battenhausen, Senior Business Manager at Evonik. “Plus, Plexiglas is capable of reproducing surfaces with tremendous precision, and without that we wouldn’t even have been able to produce the highly precise, 1,25 mm prism structures.”

Proving its merit
The first Daylight Greenhouse, which covers an area of 4,000 square meters, was completed in the Netherlands in 2014 and is operated by Ter Laak Orchids. The company was so convinced that it immediately put another greenhouse in operation in the summer of 2018—more than ten times larger than the first. “In our new greenhouse we’re saving 40 percent of our heating costs, and the greenhouse produces roughly half of the energy we need all by itself,” says Richard ter Laak, Managing director of Ter Laak Orchids. “Moreover, the climate in the greenhouse is more uniform, which means we lose fewer plants to disease and fungus.” The greenhouse functions without extra shadowing which is a huge benefit in the winter months, where up to 40 percent more diffuse sunlight finds its way to the plants. “That’s perfect for our orchids,” says Ter Laak.

Movable collectors— black painted pipes filled with water —are located underneath the roof panels and track the movement of the sun. The Plexiglas lenses bundle and direct the rays of the sun onto the collectors, heating up the water inside to harvest the energy. Source: Technokas

In addition to orchids, Daylight Greenhouses are also suitable for all other plants that like the shade. “That’s especially common for a lot of houseplants, for example. As opposed to vegetables like tomatoes or cucumbers, which usually need as much sunlight as they can get,” Van Tilborgh says. Daylight Greenhouses can be used anywhere in the world, “but regions where it gets relatively cold at night really showcase their advantages.” In hot regions, however, the energy they collect could also be used for absorption cooling. A new generation of greenhouses for many uses—enabled by Plexiglas molding compounds.

For more information:
Evonik Industries
www.evonik.com


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