Sharing photons between photovoltaic panels and microalgae for bioenergy – PURPLE SUN

The Consortium brings together seven partners innovating and rethinking the microalgae production sector. Their expertise is based on up-to-date techniques for designing and piloting greenhouses (INRA), supported by specialists in microalgae (LOV and INRIA), in innovative photovoltaic technologies (Sunpartner Technologies and Armines) and in numerical computation and impact studies (ACRI and INRIA).

Together, they proposed a new concept of positive energy culturing system for microalgae, whose purpose is to selectively use light to combine the production of algal biomass through photosynthesis and the production of photovoltaic energy.

The use of semi-transparent photovoltaic panels allows an enhanced biological productivity by maintaining light intensity at a non-photoinhibiting level, reducing mortality at high temperature while producing photovoltaic electricity.


Technological developments are oriented both by their costs and by their environmental footprints. Experiments are carried out at laboratory scale and on two specially developed outdoor pilot plants. They provide a better understanding and control of the effect of coloured light on microalgal growth rate and bioaccumulation of compounds of interest. The gains and costs are measured and extrapolated at the scale of the microalgal photovoltaic greenhouse through numerical simulation tools validated by the experimental data acquired in the pilot plants.

The project was awarded in November 2013 by the Council of the Alpes Maritimes, the concept of solar greenhouse for microalgae was awarded by the Special Jury Prize for «Climate Energy Trophy«.

From a technological point of view, biocompatible semi-transparent photovoltaic panels have been developed. They adapt automatically to the direction of sunlight. An original solar tracker was developed to assess, within one day, the performance of a solar panel along the seasons.

Many experiments were conducted in the laboratory to better understand the impact of the light quantity, quality (in terms of wavelength content), supply frequency, on growth, mortality and synthesis of compounds interest.

Two outdoor experimental platforms have been set up to test and quantify the proposed concepts in realistic conditions where light and temperature fluctuate periodically.

A numerical simulator integrating the effects of the light spectrum and temperature can now accurately predict the process productivity along the year.

The innovative concept of microalgal solar greenhouse turns out to be a promising alternative to both the photobioreactors, efficient but expensive with high energy consumption, and the raceway ponds, at lower cost, but with lower performance. The concept that we propose will achieve high productivity at reduced costs with reduced environmental footprint.

These new devices will produce microalgae synthesizing molecules of interest for animal feed, cosmetics and pharmaceuticals. In the longer term, microalgae are a promising path for green chemistry (fertilizers, bioplastics) and bioenergy (biogas and biodiesel). These photosynthetic microorganisms are indeed an effective solution for recycling the CO2 and for producing the so-called 3rd generation biofuels.

Finally, some of the concepts that are currently developed will also be applied to greenhouses, which, worldwide, are covering several million hectares.

Five publications and six patents have been produced. The Full Spectrum platform received the Special Jury Prize for «Climate Energy Trophy« of the General Council of the Alpes-Maritimes.

Microalgae are emerging as a promising solution to address a number of markets including pharmaceutics, food, green chemistry, bioenergy … Major economic developments are expected on the ten-year horizon and, in particular, the third biofuel generation, supported by a strategy of recycling and recovery of waste and residues from human activity, such as industrial CO2, or occupying land unsuitable for agricultural purposes (e.g. salt marshes, deserts …). However, competitiveness of this sector requires significant improvements 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 is to explore a breakthrough concept for microalgal production: to use the entire solar spectrum to concomitantly produce electricity and algal biomass with high lipid content. Indeed, an excess of solar energy is damageable for microalgae. It induces photosaturation and photoinhibition, synthesis of photoprotective pigments, and leads to a counterproductive increase of medium temperature.
Preliminary experiments carried out with Dunaliella salina demonstrated that the Wysips PV film (initially developed for digital devices like smartphones, tablets…), for which Sunpartner became in February 2013 the « “Nobel Sustainability Supported Clean Tech Company 2013”, was an efficient and promising way to redirect the excess of solar energy to photovoltaic (PV) electricity without affecting biological productivity. Furthermore, it proved to reduce cell mortality at high light. It is now conceivable to generate the energy required for the culturing processes, in agreement with the concept of biorefinery.
The key point is that some photons in the visible light spectrum are more photosynthetically efficient (especially for the red and blue wavelengths), while others are used with a lower yield. This leads to the technological breakthrough of Microalgal Photovoltaic Greenhouses (MPG). The proposed MPG design will be an intermediate between high cost, high yield photobioreactors and low cost, low yield open raceways, thus cumulating the advantages of each system (high yield, low cost). This original concept stands on a strong expertise on greenhouse design and management (INRA), associated with specialists of microalgae (LOV and INRIA), experts on PV technology (Sunpartner and Armines), and specialists of numerical computations and impact assessment (ACRI and INRIA).

Technological developments of the project will be directed according to their costs and environmental impacts. The objective of the project is to determine, depending on environmental parameters, the best photons to share and the best design for a photosynthesis compatible semi-transparent material. Experiments will be performed to better understand and finally master the effect of a coloured light (lacking some wavelengths) on microalgae growth rate and bioaccumulation of energetic compounds. The gains and costs resulting from redirecting a fraction of the light to photovoltaic energy will be evaluated at the scale of the MPG thanks to dedicated numerical tools validated with experimental data acquired in the proof of concept MPG.
Photon-sharing will initially be based on the already available Wysips semitransparent PV films developed by Sunpartner, but Purple Sun is also aiming at initiating the next generation of PV film dedicated to MPG applications.
We want to prove that it is possible to produce more than 40kWh/m2/year without impacting the biological yield. Purple Sun will demonstrate an improved return on investment compared to conventional low-cost raceway systems. It will contribute to reach the key targets defined by the Green Stars Institute for Decarbonated Energies (IEED).