Bioenergy water footprints, comparing first, second and third generation feedstocks for bioenergy supply in 2040

Freshwater is important for energy. Energy scenarios show increasing energy use, combined with increasing bioenergy shares. Bioenergy derives from first (food crops), second (energy crops or agricultural residues) and third (algae) generation feedstocks. There is an ongoing debate about the competition between energy and food crops. Energy crops have no direct competition with food, but an indirect one, using the same natural resources, like water. Crop residues seem a good alternative for food or energy crops. This paper gives water footprints (WFs) of first, second and third generation bioenergy (m3/GJ). Next, it compares WFs of future energy demand using different bioenergy feedstocks. WFs of energy from residues is smallest, WFs of energy crops largest. Bioenergy from algae has the largest blue WF. From a resource-use point of view, impacts of green WFs on the environment are smaller than impacts of blue WFs. Comparing different bioenergy feedstocks, residues are most favorable. With increasing bioenergy production, impacts on freshwater also increase. It is expected that increased production of first generation biofuels heavily contributes to global water scarcity. For third generation bioenergy, the application of algae would substantially increase the global blue WF. Comparing IEA scenarios, the greenest scenarios have the largest WFs, due to large contribution of bioenergy (especially in the case of energy crops and algae). Feedstocks with a relatively small WF are crop residues. The potential is enormous, but large challenges remain concerning technical possibilities to convert residues into energy carriers in combination with the possibility that not all residues are available for bioenergy.