In order to tackle climate change, a transition to a renewable based energy system is crucial. A renewable based hydrogen economy is one of the possible implementations of such a system. The world receives ample energy from the sun that can be harvested by PV solar cells and, indirectly, by wind turbines. In order to use the most optimal locations for collecting and concentrating energy from these diffuse sources, a long distance transmission network is needed. Mature and semi-mature technologies are available for all parts of the system: from collection to transmission to end-use. In an early stage of development, when new technologies have to win market share from the existing energy system, their development is driven almost exclusively by the reduction of costs per J delivered. However, if a technology should be able to deliver tens to hundreds of EJ, resource constraints can become show stoppers. Many of the newest, most cost-efficient, energy technologies make use of scarce resources and, although they may play an important role in the transition process, they can not be scaled up the level we need for a complete transition. In most cases however other technologies are available that use more abundant materials, be it often at a cost of efficiency. The issue is not only with scarce resources. The sheer size of the energy transition will also challenge the industrial capacity for the mining and production of bulk materials like steel and copper. (C) 2010 Elsevier Ltd. All rights reserved.
