5 Assumptions About Algal Biomass Yields
and Allocation
Relatively good energy balances can be achieved in studies considered here when it
is assumed that biomass and lipid yields are high, with biomass yields in the order
of 90 Mg ha
−1 year
−1 or larger (Slade and Bauen 2013; Rogers et al. 2014;
Naraharisetti et al. 2017). Such biomass yields are well beyond current yields in
commercial cultivation of autotrophic microalgae (Reijnders 2013; Rawat et al.
2016). Whether such high yields can be achieved in future widespread commercial
practice is questionable (Reijnders 2017b). A major problem for open pond cultures
is the contamination with other organisms, which can lead to instability of
microalgal cultivation (Rodolfi et al. 2008). This may be prevented by growing
microalgae under extreme conditions such as high pH or high salt concentrations.
But these conditions are not conducive to high triglyceride yields (Reijnders
2017b). And there may be problems in maintaining extreme conditions of cultivation given the vagaries of weather, such as extreme rainfall (Reijnders 2013;
Chisti 2016).
On the other hand, relatively poor energy balances may be achieved when part of
the outputs is considered wastes and all of the energy input is allocated to
non-waste outputs (e.g., biodiesel, biogas). This is at variance with the view that
mature biodiesel production systems should be designed in such a way that practically all microalgal biomass should be converted to useful outputs (e.g., Xu et al.
2011; Laurens et al. 2017).
Relatively good energy balances may be achieved when biodiesel is a product of
a production facility also generating currently highly priced co-products, when the
allocation is on the basis of current prices. A focus on such co-products can be
noted in the current development of microalgal bioenergy (Chew et al. 2017;
Laurens et al. 2017). In the case of allocation based on prices, one should evaluate
what future developments in input and output prices and the impact thereof on
estimated energy balances may be (cf. Kern et al. 2017). This type of evaluation has
not been included in the LCAs considered here. In view of recent history, one
should especially consider whether high co-product prices will be maintained when
production is much increased. The price of the biodiesel co-product glycerol collapsed when the production of biodiesel based on oils from terrestrial plants was
much increased (Reijnders and Huijbregts 2009).
6 Handling Uncertainties
In the introduction, it has been noted that it would be preferable to include in
assessments a sensitivity analysis indicating the impact of different choices
regarding the valuation of inputs, system boundaries, and allocation to outputs on
estimated energy balances (‘scenario uncertainty’). This type of sensitivity analysis
176
L. Reijnders
and Allocation
Relatively good energy balances can be achieved in studies considered here when it
is assumed that biomass and lipid yields are high, with biomass yields in the order
of 90 Mg ha
−1 year
−1 or larger (Slade and Bauen 2013; Rogers et al. 2014;
Naraharisetti et al. 2017). Such biomass yields are well beyond current yields in
commercial cultivation of autotrophic microalgae (Reijnders 2013; Rawat et al.
2016). Whether such high yields can be achieved in future widespread commercial
practice is questionable (Reijnders 2017b). A major problem for open pond cultures
is the contamination with other organisms, which can lead to instability of
microalgal cultivation (Rodolfi et al. 2008). This may be prevented by growing
microalgae under extreme conditions such as high pH or high salt concentrations.
But these conditions are not conducive to high triglyceride yields (Reijnders
2017b). And there may be problems in maintaining extreme conditions of cultivation given the vagaries of weather, such as extreme rainfall (Reijnders 2013;
Chisti 2016).
On the other hand, relatively poor energy balances may be achieved when part of
the outputs is considered wastes and all of the energy input is allocated to
non-waste outputs (e.g., biodiesel, biogas). This is at variance with the view that
mature biodiesel production systems should be designed in such a way that practically all microalgal biomass should be converted to useful outputs (e.g., Xu et al.
2011; Laurens et al. 2017).
Relatively good energy balances may be achieved when biodiesel is a product of
a production facility also generating currently highly priced co-products, when the
allocation is on the basis of current prices. A focus on such co-products can be
noted in the current development of microalgal bioenergy (Chew et al. 2017;
Laurens et al. 2017). In the case of allocation based on prices, one should evaluate
what future developments in input and output prices and the impact thereof on
estimated energy balances may be (cf. Kern et al. 2017). This type of evaluation has
not been included in the LCAs considered here. In view of recent history, one
should especially consider whether high co-product prices will be maintained when
production is much increased. The price of the biodiesel co-product glycerol collapsed when the production of biodiesel based on oils from terrestrial plants was
much increased (Reijnders and Huijbregts 2009).
6 Handling Uncertainties
In the introduction, it has been noted that it would be preferable to include in
assessments a sensitivity analysis indicating the impact of different choices
regarding the valuation of inputs, system boundaries, and allocation to outputs on
estimated energy balances (‘scenario uncertainty’). This type of sensitivity analysis
176
L. Reijnders