Energy balance of algal biomass production in a 1 ha "Green Wall Panel" plant: How to produce algal biomass in a closed reactor achieving a high Net Energy Ratio
The annual productivity of Tetraselmis suecica in a 1 ha Green Wall Panel II (GWP II) plant in Tuscany (Italy) is 36t (dry weight)ha 1year 1, which corresponds to an energy output of 799GJha 1year 1. The energy inputs necessary to attain that productivity amount to 1362GJha 1year 1, mainly given by the embodied energy of the reactor (about 30% mixing (about 40% fertilizers (11% and harvesting (10% The Net Energy Ratio (NER) of T. suecica production is thus 0.6. In a more suitable location (North Africa) productivity nearly doubles, reaching 66tha 1year 1, but the NER increases only by 40% and the gain (difference between output and inputs) remains negative. In a GWP II integrated with photovoltaics (PV) the NER becomes 1.7 and the gain surpasses 600GJha 1year 1. Marine microalgae cultivation in a GWP plant, in a suitable location, can attain high biomass productivities and protein yields 30times higher than those achievable with traditional crops (soya) When the GWP reactor is integrated with PV, the process attains a positive energy balance, which substantially enhances its sustainability.