Making greenhouses more efficient: a novel technology with lenses made from PLEXIGLAS® molding compounds

A novel technology with lenses made from PLEXIGLAS® molding compounds.

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.

“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.”

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 Röhm. “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.”