Breaking cover – the era of the ‘smart’ facade

The envelope has traditionally played a passive role in a building’s energy strategy. But advanced technologies that turn facades into valuable sources of energy generation by harnessing sunlight, heat and wind are about to transform the way buildings are designed. Stephen Cousins reports.

Belatchew Architects proposes a 14-storey extension to a Stockholm high-rise, covered in “straws” that convert motion into energy

The need to develop sources of renewable energy to power buildings has never been greater. Approximately 40% of the world’s output of raw materials goes into providing heating and cooling, ventilation, lighting, water and other services used in homes and non-domestic buildings. Given impending global fuel shortages and governments’ ambitious carbon reduction targets, the challenge being taken up by researchers and building scientists is to design buildings that will create as much or more energy than they consume.

The building envelope – offering exposed and unshaded facades on countless office blocks and factories around the world – provides an ideal location for innovative solar and wind-powered technologies. In the UK, scientists have developed the world’s first-ever transparent "printed" solar photovoltaic (PV) glass that could spell the end of the traditional PV panel, and a project at Swansea University is investigating how to transform buildings into power stations (see below).

In Germany, India and Britain, unicellular algae is being grown in facades to create biofuel and even food; and in Sweden there’s a proposal to harness “piezoelectricity”, an energy source that’s still at the research stage but is being taken increasingly seriously. Design firm Belatchew Arkitekter has proposed retrofitting a landmark residential tower in Stockholm with thousands of tiny "hairs" that generate electricity by simply swaying in the wind.

Photovoltaics incorporated

The fastest-growing sector of the PV market is building-integrated PV, whereby solar cells are incorporated in the building envelope – standard glass or cladding materials are substituted with glass laminates embedded with PV cells. This concept has been taken a stage further by start-up company Oxford Photovoltaics, which has developed a technology that “prints” organic solar cell materials directly on to glass without the need for visible wires or cells.

The super-thin layer of transparent, organic dye-sensitised cells is applied to conventional glass, and when hit by sunlight creates a potential difference, ie a voltage, that is collected by receptors running around the edge of the pane.

Oxford Photovoltaics is carrying out research into printing solar cell materials on to glass

Impressively, the system can convert about 12% of solar energy received into electricity, which is just 3% less efficient than conventional PV panels currently on the market, but it costs significantly less to manufacture, says Rick Wheal, a consultant at Arup who is helping Oxford Photovoltaics to develop the product for construction.

“The dye uses products that are relatively abundant in nature and very little energy is required during manufacture, which dramatically reduces the price. Where your average PV panel might cost around £450/m2, here you will just pay for the price of a window plus £60-100/m2 to have the coating applied,” Wheal says. The fact that the dye is made of organic compounds, not highly refined silicon, should also reduce the energy payback by several years.

The glass can be produced in various colours with corresponding differences in energy efficiency: black is highly efficient, green less efficient, red is OK and blue less so. This variety should create a more interesting aesthetic than conventional PV panels and drive interest in renewable technology, says Patrick Bellew, founding director of building services engineer Atelier Ten. “This is the most exciting product currently in development. We get a lot of resistance from clients to conventional ‘gridded’ PV panels, which don’t visually integrate into designs and it’s dangerous when the technology starts to dominate the architecture. Even if the efficiency of solar glass is a bit lower, if it looks like glass, and is cheaper and easier to apply, I expect it will be very popular,” he says.

Earlier this year, Oxford Photovoltaics received a £2m funding boost from green technology investor MTI Partners, which will be used to raise market awareness of its solar glass, as well as pay for new equipment and staff and the manufacture of the first 1 x 0.5m glazing panels at the end of this year.

“One issue that needs to be resolved is to ensure the coating isn’t removed when windows are cleaned using abrasives – we’re currently working with the firm to ensure the surface is robust and resilient,” Wheal says.

Bio-reactive facades

Designers and engineers have long dreamed of creating building facades that mimic nature and change in response to their environment. An early, highly engineered example is Jean Nouvel’s 1981 Arab World Institute in Paris, which uses photo-sensitive motor-controlled apertures to control the amount of sunlight and heat entering the building. Now a team of engineers from Arup working in cooperation with Germany’s Strategic Science Consult, have taken the bio-mimicry concept literally and installed a bio-adaptive microalgae facade on to a four-storey residential block in Hamburg.

Innovative microalgae facades appear in a proposed London development designed by Make Architects and Battle McCarthy (above) and the BIQ house in Hamburg (right)

The BIQ house, designed by Austrian firm Splitterwerk Architects as part of the city’s ongoing International Building Exhibition, incorporates 64 “double-glazed” rainscreen panels, each one filled with water and a species of algae that grows rapidly in response to direct sunlight.

A series of pipes connecting the panels circulate the algae and pump it to a plant room where, through the process of anaerobic digestion, it will be "eaten" by bacteria to produce methane gas that can be either stored locally or used to help fuel the building.

The clever part is how the process of photosynthesis in the algae also drives the building’s dynamic response to the amount of solar shading it requires. As sunlight speeds up the rate of algae growth, so the glass becomes increasingly cloudy, blocking direct sunlight from entering the building. The level of opacity can also be controlled, removing algae with the pump to adjust the amount of solar shading.

The facade is expected to create 15g of biomass per square metre of glazing, which doesn’t sound a lot. But given that as a unicellular organism algae is 30-50% efficient at converting the sun’s energy into usable energy, compared with just 15% for a good PV panel, the technology has great potential, says Arup’s Wheal. “Skyscrapers have huge, unshaded, south-facing facades and algae could have very positive benefits in terms of reducing a building’s cooling energy requirement without the need for expensive chillers. The energy produced, in the form of methane, could be used to run a combined heat and power plant to generate electricity and heat.”

But harvesting algae from facades to produce fuel may not prove to be the most commercially viable use for the technology, given the energy input required to pump the water and provide nutrients, argues Bill Watts, senior partner and biotech expert at sustainability consultant Max Fordham.

“You have to take it back to basics and ask what it is you’re trying to get from a plant. Raw chemical energy in the form of methane or petrol has value, but an order of magnitude higher than that is the energy in food for human consumption or as fodder for animals. And if you can use it to produce cosmetics or drugs then the value of the product is so immense the cost of energy put in doesn’t matter,” he says.

This principle is being applied on an “edible” microalgae facade being developed by Make Architects, building services engineer Battle McCarthy and Italian algae product supplier MicroLife, to be installed on a forthcoming development in London.

The system will comprise an internal "fence" of horizontal tubes filled with water and algae positioned behind the windows. Exhaust air from the building’s boiler and chillers will be pumped through the tubes, which in combination with solar radiation will help the algae grow. The algae will be pumped to a harvester to make fresh spirulina jam, a neutral base sauce used in food that will be sold in the building’s canteen.

Guaranteed food production

Tests are being carried out to assess the impact of variables such as the type of algae, the environmental conditions and building’s orientation. Positioning the system inside the building is vital to guarantee food production rates, says Anthony Brewer, associate director at Battle McCarthy. “London’s temperate environment and variable temperature causes algae growth rates to fluctuate. If you can control the temperature you can guarantee output, so locating the tubes internally made perfect sense. It means we’re not restricted by having to position the system on the south or west side of a building or only being able to supply enough algae on a hot day,” he says.

Battle McCarthy is working with the University of Cambridge on a similar algae system designed to produce cosmetics – a prototype has just been installed at its London office.

Belatchew Arkitekter’s “straw” cladding

The potential for noise and vibration problems have held back the development of facade-integrated wind energy, but what if "hairs" or fronds could be applied to the walls of a building, and energy from their movement harnessed to power lighting or other systems? This idea is being explored by Sweden’s Belatchew Arkitekter with its proposal to give the 26-storey Söder Torn residential block in Stockholm a new 14-storey extension, covered with thousands of composite "straws" with piezoelectric properties able to turn motion into electrical energy.

Piezoelectricity is an electric charge that accumulates in certain solid materials, such as crystals, when they are deformed. Compared with traditional wind turbines, the straws would be almost silent, have no moving mechanical parts prone to malfunction, and could operate at low wind velocities as only a light breeze would be needed to cause them to sway and generate power. Belatchew Arkitekter claims that if sufficient straws are attached to the building it would become carbon neutral, producing as much energy as it consumes.

The concept of hairy energy-producing facades is also being explored by Max Fordham and Make Architects, says Max Fordham’s Watts: “I like the idea of having a hairy building, using thousands of needles that vibrate in the wind might create enough energy to drive internal sensors or LED lights and it overcomes problems related to mechanical systems where parts need maintenance or fall off. We’ve been looking at doing it on a project in China.”

Other wind technologies currently in development might change the notion of the facade forever. Roland Schmehl, a professor at Delft University of Technology in the Netherlands, has developed a prototype "kite sail" as an alternative to a wind turbine, which measures only 25m2, but in winds of 70-90km/h it can generate enough power for 40 homes.

As buildings become more effective at reducing their overall energy demand, renewable technologies such as these will become increasingly important, explains Giorgio Buffoni, head of facades at engineering consultant Arup. “At present, active systems are only considered during the design either because clients want to show they are sustainable or it is required by regulation. But in future, as insulation, building management systems and other passive measures reduce overall energy demand, renewable sources of energy will account for a much greater proportion of a building’s power usage, rising from an average 5% or 6% today to up to 50%.”

Transforming buildings into power stations

Swansea University, BASF and Tata Steel are midway through a five-year grant-funded industry-academia research project that aims to transform “buildings into power stations”. The team is developing steel and glass products with “functional” coatings for large volume manufacture, creating walls and roofs that generate, store and release renewable energy. The products will be suitable for both new and existing buildings, particularly those where metal and glass predominate, such as retail outlets and corporate office blocks.

The project is known as SPECIFIC – the Sustainable Product Engineering Centre for Innovative Functional Industrial Coatings – and also draws on expertise from other universities and industry partners. It has secured grants from the Engineering and Physical Sciences Research Council and the Technology Strategy Board.

Last autumn, the team launched a pilot production facility for coating glass and metal in Port Talbot, Wales. IN BASF’s Coatings Partner e-journal, SPECIFIC chief executive Kevin Bygate (formerly of Tata Steel) says: “We are talking about ‘smart coatings’, or surface coatings on steel and glass which, for example, can generate heat – enough to heat the building through the year on a standalone basis.

“Scale matters a lot here – Tata Steel Europe manufactures 200 million sq m of coated steel a year. If you take just 10% of that, and convert it into a functional coating with a 5% efficiency of converting sunlight in electrical energy, we could be installing the equivalent of one nuclear power station per year every year.

“And this is just for new buildings. For retrofitting existing buildings, there is even greater potential, which could give rise to a whole new business. And there could easily be spin-off projects for other applications, such as automotive.”

Kevin Bygate (left) and David Worsley work on large-scale production of “smart” coatings

The technologies being explored cover both coating and printing, and a combination of photovoltaic technology (converting sunlight into electrical energy) and transpired solar collectors, where thermal energy can be directly harvested from the building envelope as heat energy, stored in batteries or transferred to other heat-emitting coatings in an integrated system.

The pilot production line has already produced coated glass and metal panels. SPECIFIC industrial director Paul Jones says: “It is a flexible facility in a controlled environment that uses various deposition techniques for printing and coating. It is capable of using a variety of substrates – metal, glass and plastic. And after the substrates have been treated according to the architects’ visions, the pilot production line is able to complete the prototype using sophisticated curing techniques.”

The project is now focused on scaling up the ideas from laboratory to pilot line and eventually full-scale commercial production, which is where the expertise of the industrial partners will be crucial.

“Universities can develop ‘smart’ chemicals but they are not in a position to manufacture them, especially not in large quantities,” notes Professor David Worsley, SPECIFIC research director, in Coatings Partner. “Innovation is not just about developing new molecules; it is also about the ability to bring new ideas and concepts into the market. This ‘forgotten technology’, the science of transfer, is fundamental to the work in SPECIFIC.

“We combine coating and printing, which allows us to broaden the range of functional coatings that can be applied to a wide variety of substrates. Open innovation means that everyone is invited to join in. Sharing spaces is one of the key successes so far in the project. It takes you out of the silo!”