Sustainability analysis of a society based on exergy studies – a case study of the island of Samsø (Denmark)

The Danish island Samsø has since 1997 initiated a process through which the island should reach a state where it would be able to supply its own energy. Such a situation was reached since 2005 – after having established 21 windmills – and the island is now a net exporter of electricity to the Danish power network. At the same time the buildings in the more habituated areas were connected to 4 district heating plants which generate heat from combustion of straw in some cases combined with supplementary inputs from photo thermal devices. Meanwhile, certain activities on the island, such as running the ferries, cars, factories and heating in more distant areas are still dependent on significant input of fossil fuels. The inhabitants have recently stated a wish to move on towards being independent of fossil fuels in 2030 and carbon neutral during the next decades. As a consequence the idea came up to develop a method for the “sustainability analysis” of a society which would assist in governing the transitional process in the direction of increasing sustainability. Therefore, a framework has been developed based on the concept exergy that may reveal where large consumptions are taking places. Such areas are likely to be sensible targets for action or at least increased attention. Basic methods have been developed that allows to account for infrastructure, transfers, inputs and outputs, and consumption in terms of exergy, and taking into account whether the exergy storages or flows can be considered to be renewable or not. The framework has been developed for six societal sectors: the energy sector, the public sector, the private households, the agricultural sector, the industry, commerce and trade sector and nature. Nature is here considered an activity that provides the society with an exergy that may also be of value to our societies, often referred to as ecosystem services. Based on the estimated amount of infrastructure and transfers, inputs and outputs a number of “sustainability indicators” have been developed that may be monitored over time and which may serve to indicate whether potential measures undertaken also lead the society in the right direction. An attempt to evaluate the potential importance of wastes has also been carried out as in organic waste could play an important role in acquiring the amount of bio-diesel required to run the ferries in the future. The results demonstrate that the already existing overhead in production of electricity leaves the island with many options and a great opportunity to be independent of fossil fuels in near future. In fact, it might well be that socio-economical perspectives will turn out to be the more severe obstacles in the transition process. Adjacent to this work a carbon model has also been set up to reveal the consequence of proposed measures and strategies to the carbon budget of the island (Jørgensen and Nielsen, 2014).