Designers and engineers dream of creating highly responsive building façades that mimic nature and change in response to their environment. Like flowers, they would open and close in relation to the light.

This is a new field of research but façades that make use of natural processes are already here. Over the last two years, I’ve been part of an Arup team developing bioreactive façades that cultivate microalgae as an energy source – making use of waste carbon and generating solar thermal energy in the process.

In response to German competition seeking smart façade materials, we developed a system that uses transparent containers known as flat panel photobioreactors (PBRs) to facilitate photosynthesis in a controlled environment. By the end of 2013, the system will be installed as an external shading device on a four-storey residential building in Hamburg Wilhelmsburg – the first application of integrated PBR in the world.

It works by taking advantage of the simple, unicellular structure of the microalgae to produce biomass rapidly. Not all cells in larger plants contribute to photosynthesis, but the single-cell structure of microalgae means it puts all its effort into photosynthesising. This means it grows around ten times faster than larger plants.

The microalgae circulate through the panels with water and nutrients, absorbing light and carbon and producing biomass. The part of the solar spectrum that isn’t absorbed by the algae heats the water, and this solar thermal heat is removed so it can be used in the building or stored for when it’s needed.

The PBRs are linked in a closed loop to the building’s plant room where they are fed with carbon from combustion processes in the neighbourhood. The algae is harvested and transformed into methane, with the heat generated taken out of the system by heat exchangers. It’s then either stored geothermally or fed straight back into the building using a heat pump for heating and hot water supply.

Harvesting the algae controls the amount of light that gets through the PBRs and into the building. So in the sunny part of the day you can leave the algae to reproduce and reduce solar gain, before harvesting the algae in the cooler part of the day and allowing more light through.

Because it relies on a complex, optimised system, this technology is ideal for use on a larger scale. But even on our small pilot project we hope to make a small net energy gain. We expect to produce around 15g of dried biomass per m2 per day, with solar energy converted into heat at an efficiency of 30-50%.

But I think it’s the visual nature of the system that will be a key if this approach is to be more widely adopted. Watching microalgae grow before your eyes is a sensual and direct experience whether you see it from inside or outside a building.

And these façades don’t have to be green in colour. By treating the surfaces of the PBRs or including a coloured layer you could create different effects. You could even integrate LED lighting that operates in the spectrum microalgae need to grow, so they would continue to reproduce overnight.

The possibilities are exciting and the key to implementing PBRs on a wider scale will be cooperation; it’s a technology that combines lots of different systems and skills – including façades, simulations, mechanical and structural engineering and control systems. By monitoring how people perceive and interact with the Hamburg installation we hope to evolve the bioreactive façade into a key system for zero-energy and zero-carbon buildings.