One of the elements of the exhibition “Engineering the World: Ove Arup and the Philosophy of Total Design” held at the Victoria and Albert Museum in London, and presenting the most important projects realized so far by global company Arup, is the SolarLeaf photobioreactor. The green, living facade of a building that produces microalgae and thermal energy, has left far behind all the other products, prototypes, and concepts presented at this year’s London Design Festival.
SolarLeaf is a photobioreactor (PBR) to be used as a facade of a building. Its role is to produce heat energy and microalgae. The construction of the SolarLeaf panel is quite simple: it is comprised of four glass layers. The outer ones form argon-filled insulation barriers that prevent heat loss.
The inner two glass layers form the 24-litre cavity that holds drinking water (culture medium) and green microalgae. Like other plants, microalgae – single-celled organisms, no larger than bacteria – draw on sunlight as an energy source and use it, together with CO2 and the nutrients nitrogen and phosphorus, to build up biomass in the photosynthesis process. This is is a pure source of renewable energy.
Inside the photobioreactors, microalgae are continuously supplied with liquid nutrients and carbon dioxide via a separate water circuit running through the façade of a building. In the result, microalgae can divide themselves up to two times a day and thus increase their biomass by a factor of four. Their biomass contains 23-27 kJ of energy per gram dry weight.
To avoid the microalgae sinking and remaining in suspension, the culture medium is continuously stirred by the supply of compressed air into the PBR – it works through an airlift. The high flow velocities along the inner surfaces of the bioreactor, and the lattice-like beads (scrapers) enclosed within it, inhibit the deposition of microalgae and biopollution.
At the same time, the façade collects energy by absorbing the light that is not used by the microalgae and generating heat, like in a solar thermal unit.
The biomass and heat generated by the façade of the BIQ building are transported to the heart of the system – the plant room, which is a fully automated energy management center, where solar thermal heat and algae are harvested. The heat energy produced is directly available to the house and is distributed for various uses: heating, and preheating of hot water. Excess heat energy is stored in borehole heat exchangers (80 metre-deep holes filled with brine), from which energy is drawn with heat pumps as required.
The biomass resulting from the growth of the algae is automatically harvested through an algae separator and collected in a temperature-controlled container. After the separation, most of the culture medium is returned to the PBR. Only a small amount of the culture medium is removed from the system and discharged via a drainage arrangement into the public sewer.
Harvested biomass is removed to a biogas plant, where it is conversed into methane. The conversion of biomass to methane is not done on site, because the necessary technology is not yet ready for use in residential buildings, or is difficult from a legal point of view. Instead, it is carried out externally in a biogas plant.
The advantage of biomass is that it can be used flexibly for power and heat generation, and it can be easily stored with virtually no energy loss, as well as it doesn’t require expensive storage technologies like batteries.
Moreover, cultivating microalgae in flat panel PBRs requires no additional land-use and isn’t unduly affected by weather conditions – the system can be operated all year long. The temperature in the PBR is kept constantly below 40°C in the summer and above about 5°C in the winter.
The approx. 200 square meter main algae façade comes with a net annual energy yield of about 4500 kilowatt-hours of electricity. This is somewhat more than an average household consumes in a year (3500 kilowatt-hours per year). In the BIQ building, there are 15 apartments, so only one of them could in principle be completely supplied with electricity from the bioreactors.
However, a much larger proportion of the apartments can be provided with heat, hence the bioreactor façades are used for heat generation (6000 kilowatt-hours per year) and not for producing electricity. This corresponds approximately to the supply of four apartments with heat, from the bioreactors alone. That means SolarLeaf provides around one-third of the total heat demand of the 15 residential units in the BIQ house.
Beyond residential architecture, the SolarLeaf photobioreactor façade system is suitable for a variety of different types of both new and existing buildings: industrial and commercial constructions, buildings for public infrastructure and trade.
The SolarLeaf façade system is the result of three years of research and development by Colt International based on a bio-reactor concept developed by Strategic Science Consult of Germany (SSC Ltd) and design work led by Arup.
The exhibition “Engineering the World: Ove Arup and the Philosophy of Total Design” can be seen at the Victoria and Albert Museum in London until 6 November. Photos and videos of many other projects presented at the London Design Festival, which ran from 17 to 25 September, are available on my Instagram profile.
Main picture by IBA-Hamburg GmbH/Johannes Arlt.
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