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.

Photo: Algae floating from Shutterstock

Kstor writes:

  • 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 for the letter. We invite Origin Oil and Ennesys to respond.