Sustainable greenhouse production with minimised carbon footprint by energy export

Consumer and trade organisations demand year-round healthy diets including fresh, high quality vegetables from local producers. However, greenhouse gas emissions (GHG) of heating high-tech greenhouses in northern countries are higher than transporting vegetables produced in southern Europe in unheated tunnels. The aim of this work was to assess GHG emissions when renewable energy sources were used for heating and cooling a solar collector greenhouse (SCG) in comparison with a conventional greenhouse (RG). Thermal energy generated in the SCG from solar energy was stored in an insulated water tank and different strategies were examined: no reused energy; reused energy; reused energy and excess energy transfer. Based on the semi-closed climate control strategy set in SCG and associated higher CO2 concentrations, higher marketable yields were achieved (+22%) compared to the production in the RG. The results further showed that the cumulative energy demand of the SCG can be lowered by approximately 44% compared to that needed in the RG. The carbon footprint (CF) and the water use efficiency were improved by 24% and 28%, respectively. If excess thermal energy generated by the SCG could be considered as export energy, a negative carbon footprint of 0.7 CO2-eq kg(-1) can be reached. The latter case shows that the CF can be reduced to levels of unheated greenhouses. As such, vegetable production in solar collector greenhouses can be more sustainable than in conventional greenhouses since energy and water, as well as fertiliser and associate CO2 emissions, can be saved. (C) 2019 IAgrE. Published by Elsevier Ltd. All rights reserved.