The technology is based on a phenomenon known as chlorophyll fluorescence. During photosynthesis, chlorophyll molecules in plants emit light. This light can be measured and evaluated to understand how plants are responding to certain environmental factors. Analysis of chlorophyll fluorescence to study the status of plants is nothing new in plant science. There are established methods and research in the field has been going on for a long time. But the big challenge lies in developing methods that can be applied in commercial greenhouse and indoor plantations.
Now the researchers from Chalmers and Heliospectra have developed and begun to commercialise methods to read these measurements and apply them in large commercial scale greenhouses and indoor plant growing facilities.
"The solution we have underway is about controlling greenhouse lighting by using LED lamps instead of the traditional lamps. Traditional greenhouse lighting cannot be regulated, but with LED lights you can control how much light the plants receive. It can thus be tailored to suit different plants’ requirements," says Torsten Wik, Professor at Chalmers.
But what makes the new system truly unique is that the researchers have managed to establish a connection between the signals given by the plants and the LEDs themselves. In effect, this means that the plants themselves control the brightness of the light they receive, depending on the signals they are emitting.
"As the plants react to their changing surroundings, the chlorophyll molecules emit varying light, which can be detected and interpreted by cheap sensors connected to the LED lamps above them, which adjust their brightness accordingly. In effect, the plants speak to the lamps, and tell them what adjustments they need," explains Torsten Wik.
If plants could talk…
The method offers numerous advantages. It could make it possible to control production, optimise the cultivation environment and detect quality disturbances at an early stage, which then result in a much more efficient and controllable production phase, with reduced waste and large energy savings. This is important, not only for financial burden for producers, but also globally – greenhouse lamps account for an enormous energy consumption worldwide.
According to the Swedish Board of Agriculture, electricity consumption in Swedish greenhouses was 92 GWh in 2017, and most of it is lighting with sodium lamps. At European level, consumption is significantly higher. By combining Eurostat (2015) with other sources, it is concluded that 100-200 TWh is used for greenhouse lighting, i.e. approximately as much as Sweden's total electricity consumption. LED lighting today is significantly more energy efficient than sodium lamps and can reduce electricity consumption by about 50 precent.
“Overproduction is a common problem for greenhouse growers today. To guarantee their deliveries, the farmers are forced to grow much more than necessary, to compensate for eventual waste. For growers, this new method could enable much more reliable and accurate production that can be directly adapted to demand," explains Torsten Wik.
As a next step in a new Vinnova-funded project, the control of greenhouse lighting will be implemented and tested in laboratories and in 2022 by greenhouse growers.
Text: Sandra Tavakoli
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, Professor and Head of Unit at Automatic Control at the Department of Electrical Engineering
Text: Sandra Tavakoli