The importance of this parameter
is exemplified in Fig. 1, where the area needed to produce a ton of
biomass per year is represented depending on the energy conversion
efficiency. For values as low as 0.1%, the average value for most crop
plants in field conditions [22], the requested area is very large, while
this is drastically reduced if photosynthetic efficiency reaches 3%,
a value experimentally obtained with algae in laboratory conditions
[23]. Possible improvements could eventually further increase
the biomass productivity, closing the gap with the maximal theoretical
efficiency (77 ± 5 g dw m−2 d−1, corresponding to ≈12%
efficiency [24]).