INTRODUCTION
While the first law of thermodynamics says that the quantity of energy remains constant along a given process, the second law says that the energy's quality degrades over time. The upshot of these assumptions is that, with the (remarkable) exception of the energy generated from the sun, additional energy inputs and resources are needed to construct and maintain the flourishing of modern society. Achieving effective transition to a sustainable, less carbonand energy-intensive economy rests, however, on large-scale renewable energy generation, coupled with breakthrough technologies to curb CO2 and other Greenhouse Gases (GHG) emissions from energy generation and industrial processes.
Against this background, Energy Return On Energy Investment (EROI) has been developed to assess the amount of useful energy yielded from each unit of energy input to the process of obtaining energy at the end of the production process. Phrased another way, EROI appraises the geological depletion of natural resources by calculating the ratio of the energy in a given amount of the extracted and delivered fuel to the total primary energy used in the supply chain. EROI provides a useful indication of the societal benefits stemming from the choice of different primary energy exploitation systems in terms of its life-cycle impact on energy fuels and energy balance.
Yet, EROI's implications as a means to support and inform policy-making, and the extent to which it has actually been embedded as a benchmark for regulatory choices remain largely unexplored. This contribution aims to shed light on the legal consequences of embedding EROI as part of the conceptual toolbox in selected EU environmental and energy policies – namely, financing transitional low-carbon technologies through the EU Emission Trading System (EU ETS), and spatial planning under the Strategic Environmental Assessment (SEA) and the Environmental Impact Assessment (EIA) Directives.
ENERGY RETURN ON ENERGY INVESTMENT (EROI): AN ENABLING METRIC FOR POLICY-MAKING
WHAT IS EROI ?
EROI's theoretical foundations build on Howard Odum's findings on netenergy analysis, as formally applied to fuels.EROI was eventually endorsed and developed by Charles Hall, professor of biophysical economics at New York State University.