On occasion we publish letters on Green Building Elements. In this case, Kstor, writing from France, is critical of the energy promises made by Ennesys and Origin Oil in a Jan. 11 post about growing algae on buildings using wastewater to then generate energy. In spite of real optimism to generate renewable energy using a sustainable infrastructure, the criticism here is articulate and should be carefully considered by those intrigued by the promise of algae.
The idea of growing algae on buildings using wastewater is not new. As a matter of fact, it originates from the French architect studio X-TU back in 2008 (and they have a patent on it), which will soon deliver the first prototypes of their biofacade concept in cooperation with a world-class French public laboratory on microalgae controlled cultures (see recent press releases and articles in French about it).
The problem here is more what Ennesys tries to achieve, when they promise to cover 80% of the building’s energy needs thanks to microalgae productivities of 150T/ha (see many other articles and their press releases).
Those figures are just not correct, as any microalgae specialist will immediately notice. These kinds of productivity are theorical, and can only be achieved in lab conditions with a 12 h direct flow of photons and constant temperature, pH, nutriments, carbon inputs, etc… In outdoor conditions, the maximum productivity in Paris would be around 30 T/ha with the most advanced intensified PBRs – which they do not have – as a scientific article clearly demonstrate: “Theoretical Investigation of Biomass Productivities Achievable in Solar Rectangular Photobioreactors for the Cyanobacterium Arthrospira platensis”.
It would be wise for Ennesys, and especially for their partners and investors, to “land on earth” and announce more realistic figures- unless they want to nourrish a greentech bubble…
Thanks to Jean-Louis Kindler at Ennesys for this answer:
There is abundant scientific – both private and public – literature confirming the figures demonstrated a few decades ago by NREL / DOE in the US showing average yields in the range of 30 dry g/m2/day in outdoor facilities, not even using advanced intensified PBR’s (just type “microalgae yield per acre” in any search engine).
Your assertions are based on theories and furthermore on assumptions on our system’s configuration. Our system’s performance is being measured with our real size, outdoor demonstrator.