The next generation of microalgae production systems under photovoltaic greenhouses

Microalgae are emerging as a promising solution to address a number of markets including pharmaceutics, food, feedstock, green chemistry and bioenergy. However, competition within this sector requires significant improvement on the environmental and economic aspects. One of the crucial challenges is to minimize production costs, mainly by reducing the use of exogenous energy, both in the culture and downstream processes. The aim of the Purple Sun project funded by the French National Research Agency is to explore a breakthrough concept of Microalgal Photovoltaic Greenhouses (MPG). The proposed MPG design will be an intermediate solution between the high cost-high yield photobioreactors and the low cost-low yield open raceways, thus cumulating the advantages of each system i.e. high yield-low cost. The main objective is to use the entire solar spectrum to concomitantly produce electricity and algal biomass with high lipid content. Indeed, an excess of solar irradiation is damageable to microalgae. It induces photosaturation and photoinhibition, synthesis of photoprotective pigments, and leads to a counterproductive increase in medium temperature. Preliminary experiments demonstrated that the Wysips PV film (initially developed for digital devices like smartphones, tablets…), developed by Sunpartner which became the “Nobel Sustainability Supported Clean Tech Company 2013” in February of that year, was an efficient, promising way to redirect excess solar energy to photovoltaic (PV) electricity without affecting biomass productivity. Furthermore, it was demonstrated that at high light it helps to reduce cell mortality. The key point is that some photons in the visible light spectrum are more efficient for photosynthesis - especially for the red and blue wavelengths, while others are used with a lower yield. Purple Sun is not only aiming at initiating the next generation of PV films dedicated to MPG but also the plant species for photovoltaic greenhouse applications.