BERNDES Görana a and BÖRJESSON Pål b
a) Department of Physical Resource Theory, Chalmers University of Technology and Göteborg University, SE-412 96 Göteborg, Sweden. Phone: +46 31 772 3148, Fax: +46 31 772 3150, Email: frtgb@fy.chalmers.se
b) Environmental and Energy Systems Studies, Department of Technology and Society. Lund University, Gerdagatan 13, SE-223 62 Lund, Sweden. Phone: +46 46 222 86 42, Fax: +46 46 222 86 44, E-mail: pal.borjesson@miljo.lth.se. *Corresponding author
This paper examines the water requirements in energy crops production and the energy costs and benefits of irrigating energy crops. We find that energy inputs for irrigation system establishment is relatively small, while the energy inputs for pumping can reduce the net energy output substantially if the water application is large and the combined pumping requirement of water lift and pressurization is high. We also present an estimate of the net energy response to municipal wastewater and drainage water irrigation of willow plantations. The aim is to establish whether bioenergy systems based on willow would gain or lose in net energy terms when the willow plantations are used as vegetation filters. In the case of municipal wastewater irrigation, we find that the energy input for system establishment and pumping is higher than the combined energy savings gained from reduced fertilizer requirements and substitution of N and P removal in conventional wastewater treatment plants. In the case of irrigation using drainage water from intensively cultivated cropland, we find that the energy input for establishment and pumping is lower than what is gained from reduced N-fertilizer requirements. The major reason is lower pumping requirements due to assumed location of the drainage water storage pond and willow plantation at the same site. Both vegetation filter systems have a positive net energy gain thanks to expected yield increases.