Tricky task of harvesting the sun
By Dr Adel Gougam
ABU DHABI // As an alternative to fossil fuels, solar energy is promising – it is readily available, abundant and free. But to harvest it, a range of technology types will be needed.
Each has its own advantages, but also its challenges and trade-offs. The most common is photovoltaic (PV), currently used in the UAE as rigid panels on the likes of speed radar cameras and bus stations. But for other applications, new technologies are being developed.
One of these is thin-film photovoltaics. Like their rigid counterparts, thin solar cells work by using sunlight to dislodge electrons to create an electrical current.
Where they differ is in the design and materials used. Thin-films are made by depositing one or more thin layers of photovoltaic material on glass layers that can be between a few nanometres to tens of micrometres thick. Because the layers are so thin, they can be deposited on a much larger area of glass than conventional solar panels made out of small cells connected together within the panel.
Until now, thin- film PV has been less efficient at harvesting solar energy than conventional PV. Improving this, while keeping the cost low, could put solar energy technologies within reach of more users.
At the Masdar Institute, we are working with Masdar PV to help do just that. We are developing new anti-reflective coatings for the thin-film cells that will allow the cells to trap more light. This coating is also a metallic conductor, making it easier to get the current generated out of the cell.
The material we’re working with is promising, having both good optical properties – letting in plenty of light – and good metallic conduction – helping get the energy out to the grid.
Beyond researching better materials, we are also exploring the benefit of patterning the layer for capturing even more solar energy.
When a thin-film cell layer is completely flat, some light is reflected back into the sky and is lost. But with patterning, the film is laid out at various angles that allow the reflected light rays to hit another angled surface, returning it to the cell. This can greatly improve the cell’s energy yield.
But there are several challenges. Not only do we need to find the most efficient thickness and pattern for the antireflective/conductive layer, we need one that is attractive to industry. It can’t just work in the lab; it needs to be scaled up to industrial production in a way that is cost effective.
It is our aim that, with this collaborative research, we will be able to increase the efficiency of thin-film solar cells. From currently converting around 9-10 per cent of the solar input power to electrical output, we hope to achieve 11-12 per cent while retaining the attraction of being nearly half the cost of conventional PV.
This could help not only in providing Abu Dhabi with a greater range of options to help it reach its goal of seven per cent of its energy from alternative sources by 2020, but it could also provide valuable intellectual property and an important product for the Emirate’s economy.
Dr Adel Gougam is assistant professor of materials science and engineering at the Masdar Institute of Science and Technology.