The sustainable process index - A new dimension in ecological evaluation

The Sustainable Process Index (SPI) is a measure developed to evaluate the viability of processes under sustainable economic conditions. Its advantages are its universal applicability, its scientific basis, the possibility of adoption in process analyses and syntheses, the high sensitivity for sustainable qualities, and the capability of aggregation to one measure. It has proved to be useful in industrial strategic planning. The concept of the SPI is based on the assumption that in a truly sustainable society the basis of economy is the sustainable flow of solar exergy. The conversion of the solar exergy to services needs area. Thus, area becomes the limiting factor of a sustainable economy. The SPI evaluates the areas needed to provide the raw materials and energy demands and to accommodate by-product flows from a process in a sustainable way. It relates these areas to the area available to a citizen in a given geographical (from regional to global) context. The data necessary to calculate the SPI are usually known at an early stage in process development. The result of the computation is the ratio between the area needed to supply a citizen with a given service and the area needed to supply a citizen with all possible services. Thus, it is a measure of the expense of this service in an economy oriented towards sustainability.