Page 184 - Materials Chemistry, Second Edition

172 B. Ruggeri et al.

The evaluation of the EROI of such an energy source away from ‘‘mine mouth’’
needs to compute the energy consumed to deliver and to use it at the point of
energy utilization, and this causes a decrease in EROI. In order to have some idea
about this concept, it can be considered that the EROI for oil at ‘‘mine mouth’’ is
about 20: this means that for 1 unit of energy consumed for extraction from
reservoirs, well-head treatments and new exploration, 20 units of energy are
available to society. Hall et al. (2009) estimated that at the end-user level EROI
should be at least 10 to cover the needs of society/civilization to support an energy
service. The EROI for ethanol derived from maize was instead estimated to be at
best 1.3 (Cleveland and Costanza 2010) and according to some authors (Patzek
and Pimentel 2006; Patzek 2004) less than 1. This implies that maize-based eth-
anol requires some other energy source, subsidy for its production.
EPT is a related concept to EROI. It permits to score such technology against
the time parameter. It is the time necessary to the plant to produce the energy
necessary to rebuild the plant itself. The higher the EPT value, the lower the
annual rate of useful energy and hence lower the sustainability of the technology.
In other words, EPT is the time of the operational lifetime of the plant necessary to
reach the sustainability condition, i.e., the time in which the technology starts to
feed the society.
The methodology above recalled will be applied to evaluate the sustainability of
Anaerobic Digestion (AD) technology using food organic refuse (local marked
refuse) as a substrate to produce biohydrogen plus biomethane (Ruggeri et al.
2010). EROI will be evaluated using the net energy analysis (NEA) approach
(Cleveland and Costanza 2010) with the aim of comparing the amount of net
energy delivered to society at the numerator, with the total energy required to run
the plant as the indirect and amortization terms at the denominator. The terms
useful for the energy delivered to society and net for the energy produced minus
the direct energy spent to run the plant are used in this chapter.
A comparison with other energy technologies is shown. In order to inquire the
influence of some choices, different insulation materials are also compared, and
their impact on EROI and EPT is evaluated in this chapter.

2 Methodology

2.1 General Framework

According to the concept introduced by Röegen (1976), in order to have energy
sustainability of such an energy technology, it is necessary that the technology
must be vital. Like a biological system, an energy technology must be able to
produce at least a quantity of useful energy that is able to sustain itself in order to
sustain ‘‘others’’ energy service. It necessarily needs to use only a part of the
energy source for its operational necessities and reproduction, and the remaining