The correct orientation of a greenhouse and the incline of the roof have considerable effect on plant growth and energy consumption. With the help of a computer-based model, the Dutch industry seeks to make optimal use of the sun's rays and take the loss of available potential sunlight into account when planning greenhouses. The highest radiation factor is achieved by greenhouses with their end gables running at a 7° angle to the East-West axis. But the orientation is also influenced by the season; a North-South orientation provides a higher sunlight penetration across the whole year than an East-West orientation but an East-West orientation is better in the spring and late autumn at certain periods of the day - especially in the morning and early evening. The incline of the roof influences how the rays of sunlight split. Today's greenhouses have a roof incline that varies between 21° and 28°. Inclines above 25° are better with regard to solar penetration, especially during the darker winter months, but contribute to a larger area for potential heat loss. "Greenbusiness International" E-mail: info@thalackermedien.de www.gb-i.net