In modern commercial greenhouses the environment of the plants are controlled down to the very last detail. Water, heat, light and nutrients: nothing is left to chance. Scientists have now developed a software tool that makes it possible to control when the plants are supplied with artificial light or left darkness based not only on an on/off timer but also on the basis of when the light requirement is greatest and when the cost of power is lowest.

Senior scientist Carl-Otto Ottosen from the Department of Horticulture at the Faculty of Agricultural Sciences, University of Aarhus, is one of the scientists participating in the project.

- Commercial Danish greenhouses are facing huge challenges because their environmental obligations keep increasing while at the same time there has been a veritably explosive increase in energy costs in recent years, says the senior scientist.

The scientists have already developed a system (IntelliGrow) that uses knowledge of plant photosynthesis to calculate the optimum climate in the greenhouses so that energy is only added when the plants can utilise it. For example, plants are given added CO2 and heat on bright, sunny days, while on days with grey skies less heat and CO2 are added. This reduces the energy consumption in the greenhouses by 10-30 percent.

During long periods with grey skies it is still necessary to use artificial light in order to optimise production. But why not use the light when it is at its cheapest and only when it is needed instead of having a timer controlling the light and only turning it off when there is lots of sunshine?

- We know how energy costs vary throughout the day. The price depends on consumption, so it is normally most expensive around 7-8 o’clock in the morning and 5-8 o’clock in the evening and cheapest during the night. We also receive daily weather forecasts including, not least, cloud cover, and we receive it rather accurately per postal code. The model uses this information to propose artificial light control that as far as possible only turns on the lights during periods with grey skies and when power is not at its most expensive, explains Carl-Otto Ottosen.

- So far, the system is offline but our ambition is that it becomes directly online, says Carl-Otto Ottosen. In the ongoing research the scientists will clarify more precisely when the plants require light and include in their calculations when it is most economically feasible for farmers who produce their own power to sell it to the public grid.

The project, which is financed by Energi Fyns Almene Fond og Udviklingsfond, is carried out in collaboration between the Faculty of Agricultural Sciences, University of Aarhus, and Maersk Mc-Kinney Moller Institute, University of Southern Denmark (associate professor and PhD Bo Nørregaard Jørgensen and engineer Martin Jebjerg Sant).

For more information please contact: Senior scientist Carl-Otto Ottosen, Department of Horticulture, Faculty of Agricultural Sciences, University of Aarhus, telephone: +45 8999 3313, e-mail: CO.Ottosen@agrsci.dk