This book has shown that sustainability assessment of renewables-based technology is still at an early stage. It has been shown in particular that there are a large number of metrics available, being quite diverse in nature, presented by academics, public and private financed research institutes, and industry. The question may be raised if, in the long run, we are moving towards one single generic assessment tool. This may be very doubtful given the diversity of renewables-based technology and the questions that have to be answered. According to Levett (1998), we should take a modest ‘fitness-for-purpose’ approach in developing indicators, i. e. using different indicator sets for different purposes, rather than straining to produce a single definitive set of sustainable development indicators.
Anyhow, there is an obvious need to have appropriate sustainability metrics for renewables-based technology. Renewable energy, for example, is a key element in energy policy worldwide nowadays. Renewable energy is important in contributing to sustainability and security; it helps to meet emissions targets, it stimulates research and development of new technologies; it provides a set of diverse energy and material sources; and it contributes to rural development by putting forward new opportunities for agriculture. Last but not least, it makes national economies more independent of oil – producing countries. In order to quantify the sustainability of new renewables-based technology that claim to be effective here, metrics are of key importance.
A nice example of the need is the 2003 EU Directive on ‘biofuels and other renewable fuels’, stating that 2% of the fuels for transportation should be biofuels at the end of 2005, and 5.75% at the end of 2010. This directive presumes a black-and-white situation: either fuels are renewable or non-renewable. A careful analysis shows that different types of biofuels rely on renewables to a different extent. In other words, a refined approach relying on adequate sustainability metrics, could be very welcome here (Chapter 5, Chapter 7, Figure 7.5).
The example shows that our industrial society is an industrial network. One conclusion that can be drawn is that we may need sustainability metrics for both ‘renewables-based’ and ‘non-renewables based’ technology, including prominent information on the degree of renewables being used. This will help us better understand to what extent and how we rely on natural resources. Bearing the industrial ecology theory in mind, a second conclusion may be that we should put effort into quantifying to what extent technology relies on recovered waste materials instead of both virgin renewable and non-renewable resources.
 weighting of impacts.
 preservation of sufficient temperate, boreal and tropical forests to ensure that biological diversity, recreation and natural beauty are maintained;
 mixed-use plans for maintaining forests through a combination of sustainable harvesting and management for environmental and recreational goals;
 plantation forest management to maximize yields. This helps to reduce the pressure to commercially exploit forests that could be preserved, or those that are managed under mixed-use plans.