It is a delectable luxury to be able to eat fresh, Danish-grown lettuce and herbs in the midst of winter and a sight for sore eyes to have Danish potted roses and campanula in the home in the dark of the Danish winter. However, growing flowers, vegetables and herbs in greenhouses in the winter requires a lot of energy. Scientists from Aarhus University are therefore collaborating with the horticultural industry and related companies to find solutions that can reduce the consumption of expensive and climate-unfriendly energy.

In a new project researchers and commercial gardeners will work on developing the future version of artificial lighting control in which the control system is connected to the power system’s smart grid. Smart grid is a network system that continuously uses information about current electricity consumption in order to improve the efficiency, sustainability and economy of the power system.   

- The horticultural greenhouse industry is among the top five users of electricity so there is every reason to seek savings and find new solutions, says the leader of the project associate professor Carl-Otto Ottosen from Aarhus University.

Energy demands fluctuate

The goal of the Danish energy policy regarding the electricity network of the future based on renewable energy sources places great demands on controlling energy use in the future. Production of electricity from the sun and the wind fluctuates greatly and results in large fluctuations in the price of power during the course of a day and on a day to day basis.

Commercial greenhouses use a lot of artificial lighting to ensure the best product quality but have a very set pattern of light control. Previous collaboration between Aarhus University and the University of Southern Denmark in the pilot project DynaLight demonstrated that there are potential energy savings of between 15 and 30 per cent by using a dynamic control of the artificial lighting.

With dynamic lighting control the lights are only on when they are needed instead of being on all day no matter whether the sun is shining or not.

- Dynamic control of artificial lighting results in an artificial light pattern that is irregular during the individual day and from day to day, says Carl-Otto Ottosen.

Keeping this in mind, it is also necessary to pay heed to the plants’ biology. The plant species have different needs with regard to the amount and the timing of light during a 24-hour period dependent on whether they are short day plants, long day plants or day neutral plants.

Plant requirements

In the new project the goal is to optimize plant growth in relation to energy costs with dynamic control of artificial lighting and by integrating commercial greenhouses with the power grid through DONG Energy’s Power Hub concept.

- This will enable the commercial greenhouses to adapt their production dynamically to fluctuations in the electricity price. The greenhouses will thus be prepared for the smart grid. If, for example, the power grid is on the way to becoming unbalanced, the greenhouses can regulate by turning the lights on or off for shorter or longer periods, explains Carl-Otto Ottosen and continues:

- Turning the light on or off can be critical for some plants because they are sensitive to 24-hour light but we do not know if anything happens with 24-48 hours of light.

The plant species used in the project are the short day plants lettuce, chrysanthemum and kalanchoe, the long day plant campanula, and the day neutral plants potted roses, orchids, and selected herbs, that cannot handle 24 hours of light.

The project, which is a collaboration between Aarhus University, University of Southern Denmark, University of Copenhagen and Technical University of Denmark, the companies Phillips, DONG Energy, Lindpro and GreenTech, and the commercial greenhouses RosaDanica, KnudJepsen, Sogoteam and Legro, is supported by grants from the development and demonstration programmes GUDP and EUDP.

For more information please contact: Associate professor Carl-Otto Ottosen, Department of Food Science, e-mail: co.ottosen@agrsci.dk, mobile: +45 21 22 92 08