Around much of Australia, the presence of solar panels on roofs has become commonplace.
Courtesy of silicon blocking out light, however, conventional solar panels are largely absent from commercial building windows. Nor are they commonplace on walls. From an energy generation viewpoint, much space across 10-, 20- or 50-storey facades is non-productive.
Interest in changing this is growing. Last December, researchers at Monash University secured grants worth a combined $1.59 million from the Australian Renewable Energy Agency’s $29 million solar energy fund to work with the CSIRO, Flinders University, Macquarie University and commercial partners CSR Viridian and GreatCell Solar to test two types of cells made from materials which can be used on facades.
Associate professor Jacek Jasieniak, director of the Monash Energy Materials and Systems Institute, received $0.75 million to develop cells made from compounds known as mixed metal halide perovskites. Materials scientist and associate professor Chris McNeill, meanwhile, received $0.84 million to create solar cells made from semiconducting plastics.
The idea, Jasieniak says, is to develop materials which can be integrated within buildings and serve as part of the façade. At the moment, he says up 80 per cent of solar energy which strikes commercial windows is reflected back outward through glazing.
“You have to ask yourself, why are we cutting 70 to 80 per cent of the light and reflecting it back out,” he said
“The premise comes, ‘how do we make that window into something that produces electricity and doesn’t waste excess energy by reflecting it out?’”
According to Jasieniak, the push toward integrated solar cells has been going on for some time. Whilst conventional silicon cells could be used as part of the wall, their light-blocking properties mean that their use on most windows would be restricted to a largely impractical arrangement whereby silicon modules were spaced to allow light through.
Because of this, he says attention is shifting to alternative materials and devices.
Jasieniak says the chemical structure of perovskites enables them to be made into effective solar cells using relatively straightforward processes. For many types of cells, he says achieving efficiency in terms of how well the material absorbs light, converts energy into electrical charges and then collects those charges has proved difficult. He says high efficiency has proven to be possible with perovskites.
Further advantages of perovskites involve the ability to make the material very thin and to control the amount of light the cells allow though by altering their thickness.
The cells, he says, can be made to around the thickness of just one thousandth of a human hair. Moreover, it is possible to alter the amount of light which the material allows to pass through – known as the average visible transmission (AVT) – by altering the thickness of the material. This is achieved by using printing processes to make the device controllably thick. Though this, Jasieniak says you can readily create devices with AVT of up to 40 per cent and still achieve functional devices.
Though he stresses that this differs across buildings in terms of position in respect of the sun and location within the country, Jasieniak says the cells could generate the equivalent of up to 15 to 20 percent of a building’s total energy consumption. As well, if the cells are coupled with the lighting control system, this would deliver lower lighting costs.
How soon this will happen depends upon overcoming obstacles such as scalability, stability and cost. As of yet, Jasieniak says the technology has been demonstrated only on a small scale. To be used effectively, it will have to be able to work as a façade which is equivalent in size to a regular window. These smaller scale tests have also highlighted some concerns regarding stability. Through his research, Jasieniak is hoping to demonstrate both scalability and stability.
On cost, Jasieniak says to be competitive, the cells will have to be comparable in price to that of regular windows – anywhere from $150 per square meter to $1,000 per square metre.
By partnering with CSIRO, CSR Viridian and GreatCell Solar, he says the research has been aligned to enjoy a natural pathway to commercialisation.
He says the potential for integrated solar should not be underestimated. At the moment, he said solar is being limited to rooftop solar and panels in large fields.
Nevertheless, he said there are costs to putting up roofs, bricks and windows whether solar technology is incorporated into these or not. If solar cells could form part of the façade without increasing the overall costs of these facades, he says the opportunities to capture and use sunlight on windows and walls is significant.
“At the moment, only one per cent of all solar cell technologies are installed as building integrated products,” Jasieniak said. “If you can start to couple those cost factors, then you know that solar technology in the future will actually form the façade of many, many buildings.
“It is not certain when it will happen, but it will happen.”