Unveiled in a pilot project at the International Building Exhibition (IBA) in Hamburg in 2013, the world´s first bio-reactive façade generates renewable energy from algal biomass and solar thermal heat. The integrated system, which is suitable for both new and existing buildings, was developed collaboratively by Strategic Science Consult of Germany (SSC), Colt International and Arup.
The biomass and heat generated by the façade are transported by a closed loop system to the building’s energy management centre, where the biomass is harvested through floatation and the heat by a heat exchanger. Because the system is fully integrated with the building services, the excess heat from the photobioreactors (PBRs) can be used to help supply hot water or heat the building, or stored for later use.
The advantage of biomass is that it can be used flexibly for power and heat generation, and it can be stored with virtually no energy loss. Moreover, cultivating microalgae in flat panel PBRs requires no additional land-use and isn’t unduly affected by weather conditions.
In addition, the carbon required to feed the algae can be taken from any nearby combustion process (such as a boiler in a nearby building. This implements a short carbon cycle and prevents carbon emissions entering the atmosphere and contributing to climate change.
Because microalgae absorb daylight, bioreactors can also be used as dynamic shading devices. The cell density inside the bioreactors depends on available light and the harvesting regime. When there is more daylight available, more algae grows – providing more shading for the building.
Full-scale pilot project
SolarLeaf façade was installed for the first time on the BIQ house at the IBA in Hamburg in 2013. In total, 129 bioreactors measuring 2.5m x 0.7m have been installed on the south-west and south-east faces of the four-storey residential building to form a secondary façade.
SolarLeaf provides around one third of the total heat demand of the 15 residential units in the BIQ house.
How SolarLeaf works
The flat photobioreactors are highly efficient for algal growth and need minimal maintenance.
SolarLeaf’s bioreactors have four glass layers. The two inner panes have a 24-litre capacity cavity for circulating the growing medium. Either side of these panes, insulating argon-filled cavities help to minimise heat loss. The front glass panel consists of white antireflective glass, while the glass on the back can integrate decorative glass treatments.
Compressed air is introduced to the bottom of each bioreactor at intervals. The gas emerges as large air bubbles and generates an upstream water flow and turbulence to stimulate the algae to take in CO2 and light. At the same time, a mixture of water, air and small plastic scrubbers washes the inner surfaces of the panels. SolarLeaf integrates all servicing pipes for the inflow and outflow of the culture medium and the air into the frames of its elements.
The maximum temperature that can be extracted from the bioreactors is around 40 degrees Celsius, as higher levels would affect the microalgae.
The system can be operated all year round. The efficiency of the conversion of light to biomass is currently 10% and light to heat is 38%. For comparison, photovoltaic systems have an efficiency of 12-15% and solar thermal systems 60-65%.
The bio-responsive façade aims to create synergies by linking different systems for building services, energy and heat distribution, diverse water systems and combustion processes.
The key to a successful implementation of photobioreactors on a wider scale will be cooperation between stakeholders and designers. It is a technology that benefits from strong interdisciplinary collaboration, combining skills in environmental design, façades, materials, simulations, services, structural engineering and control systems.
What is most needed is an understanding and view of the systems’ benefits for the user, the building and the environment.