Page 92 - Advances in bioenergy (2016)

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holds for novel sources of electricity such as photovoltaic cells and wind power systems. A
meta-analysis of operational studies did, e.g., show an EROI of on average 19.8 for wind
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power systems. It has been suggested that EROIs of more than 5 will be required to maintain
quality of life in the absence of readily abundant fossil energy and this criterion has been used
previously in the context of microalgal biofuels. 68,69 In line with this, an EROI of at least 5 is
used here as energetic criterion for a suitable liquid algal biofuel.

LIFE CYCLE ASSESSMENT

Products, such as biofuels, have life cycles, which stretch ‘from cradle to grave’, or from

resource extraction to emissions and waste disposal. LCAs are often considered the proper
way to compare the energetic and environmental performance of specific biofuels with other
fuels or types of energy supply. 27,36,38,39,70,71

LCA has been developed for analyzing current products from resource extraction to final waste
disposal or emissions. Apart from analyzing the status quo, LCAs may also deal with novel
products and production processes. The latter type of assessment has been called
consequential, as distinguished from the analysis of status quo products, which has been called
attributional. 72-74 LCAs of microalgal biofuels are often consequential, as they refer to future
commercial production systems, which are as yet not operational.

Different data and approaches may be needed in attributional and consequential LCA. 27, 73-77
Regarding microalgal biofuels, knowledge often partly or fully relates to the research and
development stage or to the limited production stage. Extrapolation of such knowledge to
future production systems gives rise to large uncertainties. The same holds, as pointed out
before, for estimation of future yields of algal biomass and lipids.

Also, future microalgal biofuels may be subject to currently unavailable environmental
improvement options and may have to operate under conditions that diverge from those that are
currently common. The latter conditions may, e.g., include higher resource costs, which are
conducive to resource efficiency. Also, the comparison with other products may be different in
consequential LCA. For instance, it is expected that life cycle emissions of fossil transport
fuels will go up in the future, whereas their EROI will go down, 77-79 and this may increase the
relative attractiveness of microalgal biofuels if compared with fossil fuels, although not if

compared with solar and wind energy. 63

LCA is generally divided in the following four stages 70, 71 :

goal and scope definition;

inventory analysis;

impact assessment; and

interpretation.

In the goal and scope definition stage, the aim and the subject of LCA are chosen. This implies