Biofuels from Microalgae: Biodiesel

It has been argued that the energy output from microalgal biofuel pro- duction should at least be 5–8 times the energy input, apart from solar irradiation driving algal photosynthesis. There is as yet no commercial production of microalgal biodiesel or large-scale demonstration project to check whether this criterion regarding the energy balance can be met in actual practice. There is, however, a set of relatively well-documented peer-reviewed scientific papers esti- mating energy inputs and outputs of future autotrophic microalgal biodiesel pro- duction. Energy balances for biodiesel from autotrophic microalgae grown in ponds tend to be better than for biodiesel from such microalgae grown in bioreactors. The studies regarding energy balances for biodiesel derived from microalgae grown in open ponds are considered here. None of these energy balances meets the criterion that the energy output should exceed the energy input by a factor 5–8. Estimated energy balances are variable due to divergent assumptions about microalgal vari- eties, applied algal and biodiesel production technologies, assumed parameters and yields and due to differences in system boundaries, allocation, and the use of credits. The studies considered here could have done better in handling uncer- tainties in estimated energy balances.