Abstract
Human society is now at the beginning of a transition from fossil-fuel based primary energy sources to a mixture of renewable and nuclear based energy sources which have a lower Energy Return On Energy Invested (EROEI) than the older fossil based sources. This paper examines the evolution of total energy demand during this transition for a highly idealized energy economy. A simple model is introduced in which the net useful energy output required to operate an economy is assumed to remain fixed while the lower EROEI source gradually replaces the older higher EROEI primary energy source following a logistics substitution model. The results show that, for fixed net useful energy output, total energy demand increases as the ratio EROEInew/EROEIold decreases; total energy demand diverges as EROEInew approaches unity, indicating that the system must collapse in this limit.
Highlights
Energy plays a critical role in enabling and sustaining human societies and is subject to strict physical conservation laws arising from thermodynamics
For the purposes of this paper, which seeks to isolate and examine the effect on total energy demand precipitated by a transition from a high Energy Return On Energy Invested (EROEI) primary energy source to a lower EROEI source, we shall assume that the transition follows this model
We note that the manufacture of the solar PV systems will require an up-front energy investment, which is returned over the life of the system; provision of this upfront energy demand would likely occur from fossil fuel systems
Summary
Energy plays a critical role in enabling and sustaining human societies and is subject to strict physical conservation laws arising from thermodynamics. With these considerations in mind, the net useful energy available for needs other than the energy system itself, Enet, can be expressed in terms of the energy system output energy, Eo, and the diverted energy, Ediv as Comparing this expression to the definition of efficiency given earlier, the distinction between the two concepts should become clearer: EROEI is a measure of how much of the useful energy delivered by the system must be diverted or otherwise used to create and operate the energy system and, as has been argued elsewhere [3], plays a crucial role in the sustainability of human civilization.
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