Innovative technologies for an efficient use of energy

Efficient use of energy in greenhouses has been subject of research and development for decades. The final energy efficiency, e.g. the amount of energy used per unit of product, is determined by improvements in energy conversion, reductions in energy use for environmental control and the efficiency of crop production. The new European targets on reduction of CO2 emission have resulted in a renewed interest in innovative technologies to improve energy efficiency in greenhouses designed for Northas well as South European regions. In this paper an overview of the recent developments is presented from both the Northwest European as well as the Mediterranean perspective. The developments range from new modified covering materials, innovative and energy conservative climate control equipment and plant response based control systems, to integrated energy efficient greenhouse designs. INTRODUCTION After the first “energy crisis” in the early 1980ies, where the limited supply of energy caused the first significant increase in energy prices, the energy use of greenhouses has again become a major research issue. The need for (energy) cost reduction becomes of higher importance when energy forms a substantial fraction of the total production costs. For Italy, it has been calculated that energy use for conditioning is already about 20-30% of the total production costs (De Pascale and Maggio, 2004), while in France it is 12-14% on average (Boulard, 2001) and 22% for vegetables, which is comparable to the northern regions (van der Knijff et al., 2004). The absolute use, however, differs between the specific locations: e.g. for Finland the total energy consumption, has been estimated at 1900 MJm per year (Olofsson et al., 2006), for The Netherlands 1500 MJ m (van der Knijff et al., 2004) and for southern France 500-1600 MJ m (Vesine et al., 2007). With the recently more pronounced interest in global warming and climate change, the use of fossil fuel is on the political agenda again (see Al Gore’s recent movie: An inconvenient truth). The international Kyoto protocol resulted in a new worldwide goal and many governments have set maximum CO2 emission levels for different industries, e.g. for The Netherlands: -30% CO2 emission in 2020 compared to 1990. The greenhouse industry is thereby again confronted with economical, political and social pressure to reduce the energy use and improve the energy efficiency. There are mainly two ways to increase the energy efficiency: • reduction of the energy input into the greenhouse system • increase the production per unit energy. The first strategy can be divided in two different parts: 1) efficient conversion technology to maximize the conversion of the energy source into a usable form (e.g. heat, 49 Proc. IS on Greensys2007 Eds.:S. De Pascale et al. Acta Hort. 801, ISHS 2008 cold, light) and 2): the reduction of the energy loss to the environment. The increase of the production per unit of energy, can be achieved in many ways, especially under sub optimal growing conditions. In fact, all cultivation measures which increase the production like improved irrigation, better nutrition, pest and disease control, a better utilization of the available greenhouse area etc, in the end also improve the energy