18.12.2008

Major energy savings sought in market gardens
A curtain of light between the rows of plants to replace high-energy lamps

TAMK University of Applied Sciences in the City of Tampere (Finland) has developed a unique lighting method intended for use in commercial greenhouses. Here the light required by the plants is produced by means of LED technology between the rows of plants. It is estimated that in the future the method will achieve savings of up to one half of the present vast need for energy in hothouses.

For use in the hothouse, the curtain of light between the rows of plants is an idea cultivated by Matti Horppu, lecturer at TAMK University of Applied Sciences (left) and Managing director Esa Kivioja of the company KKK-Vihannes Oy. The use of the curtain has been piloted in the cultivation of cucumbers. High resolution image (480 Kb) Photo: Niko-Matti Kivioja

The curtain of light developed by TAMK University of Applied Sciences has been internationally patented and a utilization model has been registered in Finland. The curtain of light is based on low-energy LED technology and it is currently being piloted. The company NETLED OY holds the utilization rights to the curtain and aims to commercialize it. There is market potential of the curtain of light in the Nordic countries, in Canada and due to a significant period of darkness also in central Europe.

The curtain of light makes it possible to provide the light required for plant growth with much less consumption of electricity than with the current high-pressure sodium lamps. The power of the light in the LED of the curtain and the colour temperature can be adjusted to optimal: according to recent research it has been estimated that a plant prefers to use a different colour temperature during it growth phase than at the time of bearing fruit.

Thanks to the curtain of light the lighting, heating and ventilation in hothouses can be achieved in many ways more easily that with present systems. High-pressure sodium lamps require sturdy support structures, cables and transformers. Moreover, their lifespan is only a third of the life of LED lights.

It is planned to make the curtain of light into a warp knitted net structure which will permit air to circulate among the plants. The curtain and its LEDs are to be about one metre wide between the rows of plants and could be easily rolled up when the plants and the building need maintenance work. For example, a hothouse with floorspace of around 2 hectares would require some 12 kilometres of LED curtain.

That same 2-hectare hothouse planting at present requires 8,000 400-watt high-pressure sodium lamps, thus the overall efficiency of the lighting is no less than 3.2 megawatts. Nevertheless, only 10 per cent of the energy from the lamps turns into light and even of this the lion’s share does not directly shine on the growing surfaces of the leaves. All this energy mounts up to an annual energy bill of about half a million Euros per year.

High-pressure sodium lamps have a high surface temperature and if placed between the rows of plants they cause burn damage to leaves and fruit. If placed high up such lamps give off a lot of heat, making it difficult to maintain a steady growing temperature of 16 to 20 degrees centigrade and economical channeling of the air flow.

The curtain of light is also estimated to be of use in due course in the cultivation of flowers and due to its versatile light colour capacity also in decorative and interior lighting. The method is also suitable for cultivation without day light (the cave cultivation, etc) of lettuce and herbs in densely built-up areas. The development of the curtain has been a part of the TAMK R & D work, and it has been funded among others by Finnish Funding Agency for Technology and Innovations (Tekes) - those participating in the development work included the company KKK-Vihannes Oy of Honkajoki which produces 700 tons of organic tomatoes annually.

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