Imagine the windows in your home harvesting the sun's energy to power your entire household's electrical needs. It may sound like something out of a movie, but it is closer to reality than you'd think.
We're quite familiar with solar cells that heat our water and generate electricity in homes and other buildings. But a team of Malaysian scientists is now taking solar technology a step further – by adding power generating capability to building features such as windows, blinds, sun roofs and canopies.
The source of their inspiration stems from nature and the most important biochemical process on the planet – photosynthesis.
"We are developing thin-film photovoltaic devices that can be used to create an electricity-generating window," says Prof Dr Norani Muti Mohamed. "The process is a kind of artificial photosynthesis. We use a dye to capture the light energy just as plants use and process chlorophyll to capture the sun's energy."
Norani is the director of the Centre of Innovative Nanostructure and Nanodevices (COINN) at Universiti Teknologi Petronas (UTP). She is also a professor at the Fundamental and Applied Sciences Department.
"Initially researchers extracted chlorophyll to study the process of photosynthesis in plants," she explains, adding that eventually this led to the use of a dye sensitiser together with the metal oxides to generate electricity.
"Then in 1991, scientists Brian O'Regan and Michael Grätzel showed that dye-sensitised solar cells (DSC or Grätzel cells) had a higher energy conversion efficiency," she says.
Norani has built upon this research since 2009, using nanotechnology and the latest iteration of the DSC technology engineered at the lab at COINN to create an electricity-generating window.
In Malaysia, according to Norani, the technology is mainly targeted for Building Integrated Photovoltaic (BIPV) for roofing deployment. For this third generation solar technology, solar cells can be fixed as non-viewing windows, blinds, glass walls, sunroof or canopy.
"It's extremely suitable for modern architectural design where glass structures are used to enhance the building's characteristics," she says, adding that the dye solar window is the only product that can be integrated into a building's architecture.
"There are large windows areas in commercial and residential structures in Malaysia, which offer a huge opportunity to generate solar energy. This will create more sustainable urban environments, where buildings become energy self-sufficient and energy secure."
A 2017 news report pointed out that solar cell technology was the key in tapping into the energy potential of windows and other transparent objects. The report estimated that five billion to seven billion sqm of glass surface in the United States could be used to meet 40% of the country's energy demand.
Solar energy is a clean, renewable and an abundant energy source in Malaysia. It has been harnessed for solar thermal applications such as water heaters and electricity generation. For the latter, solar or PV cells – generally mounted on the roof of a building – are used to harvest light energy from the sun and convert it into electricity.
But these conventional solar cells have some drawbacks, among them being the cost and limitations that include performance under cloudy skies and diffused light conditions.
The DSC technology overcomes these downsides. The technology has been tested in a solar hut built at UTP's Solar Field Testing Facility. Solar windows installed here can generate enough electricity to charge a mobile phone, for lighting, as well as powering household appliances.
Trials showed that the solar windows performed well in low light, working longer hours in a day and giving power output comparable to – or better than – the conventional PV cells installed on the roof.
"In diffused light, the performance of the conventional PV cell drops abruptly, limiting its application to only rooftop deployment. This is not really efficient in Malaysia's real solar condition," Norani says, pointing to the fact that Malaysia experiences significant cloud cover.
The solar windows also have a higher tolerance for elevated temperature and have minimal performance degradation.
"This is due to the high stability of the active components, which are not exposed to the direct sunlight unlike those deployed on the roof. The solar windows need minimal maintenance as they are enclosed and protected by the glass panels," she says.
The solar windows are bi-facial (have two faces), which means that indoor light or sunlight coming from other openings can also be captured, thus increasing the electricity output.
Norani is excited about the prospects for this new technology, explaining that Malaysia requires solar technology that can generate electricity even in low light conditions. "Conventional PV cells work best from 9am to 4pm, but the solar windows work longer hours from 7am to 6pm."
She points out that even for terraced houses, which typically do not have many windows, there is potential. "The lack of glass windows can be compensated by having glass canopies and walls," she says, adding that using mixed energy sources to power the house will allow for 10-20% savings in monthly electricity bills.
She believes that the product's low manufacturing cost and use of readily available non-toxic raw materials means that green energy has become a more economically viable option in Malaysia.
"It's predicted that the cost of a properly scaled-up, fully optimised dye solar cell is about one-fifth of the conventional solar panel," she says.
It's also a boost for rural electrification programmes where solar windows can be deployed in a solar farm without needing much ground area. "Other applications will be to power the control and monitoring systems, such as security surveillance, remote monitoring, traffic sign and street lighting," she adds.
To date the invention has bagged several medals in international exhibitions: gold at the International Invention, Innovation & Technology (ITEX) 2012; silver at the Malaysia Technology Expo 2011; gold at the Innova Brussels Exposition 2010; and it won the best green invention award at ITEX 2012.
The next step, Norani says, is commercialisation. "We are planning to apply for another near-commercialisation grant from the Ministry of Energy, Science, Technology, Environment and Climate Change, to fund a research initiative that aims to resolve engineering-related problems for the integration of the DSC panel into the building facade, such as integration of panels, connections and wiring."
She discloses that at the International Genetically Engineered Machine (IGEM) 2017, a few potential collaborators expressed interest in commercialising the DSC to be used for the roof or wall of bus stops.
"Others have expressed interest to collaborate in green building projects and integrate the DSC panel in the facade of greenhouses to power the ventilation system," she says, adding that she's also received queries from a company keen on marketing the invention.
Dye-sensitised solar cells comprise transparent conductive glass substrate printed with a thin layer of titanium dioxide (TiO2) photoelectrode material and coated with monolayer dye sensitiser, which acts like chlorophyll in the leaves.
The electrode is sandwiched together with a counter electrode, and an electrolyte containing a redox couple fills the gap between the electrodes (see the graphic above).
When the sun radiation strikes the dye molecules, the electrons get excited and enter the conduction band of photoelectrode material, flow through the photoelectrode films to the transparent conducting oxide, and then to the external circuit.
The electrolyte receives electrons from the circulated electrons through the external circuit at the conducting catalytic cathode, thus completing the circuit.