Page 25 - University of Pretoria RESEARCH REVIEW 2016

SUSTAINABLE CLEAN ENERGY AT LOW COST AND HIGH EFFICIENCY
It is widely recognised that sustainable energy at low cost would contribute to poverty alleviation and arrest climate change. Fossil fuels for energy contribute directly to global warming by adding carbon dioxide to the atmosphere, as well as to deforestation and climate change. The growing world population adds further urgency to the need to develop systems that can generate cost-effective, efficient, clean and renewable energy.
Professor Mmantsae Diale is the research leader of the Solar Energy Collection and Conversion group in the Department of Physics. Her research is directed towards finding low-cost solutions and efficient technologies to collect and store solar energy. Silicon has been used in harvesting solar since the discovery of photovoltaics (PV) several decades ago. Over approximately the same period, the cost of PV has reduced from $76.00 per watt in 1976 to $0.30 in 2016, with the price of PV now lower than that
of electricity generated from coal. However, clean energy is still expensive for those who need access to off-grid solar power the most.
Professor Diale notes that there are two main challenges associated with the current PV approach: first, the cost of available materials; and secondly, the ability to store the captured energy effectively for times of inclement weather. Her group’s research aims to produce a solar-driven system that will
both collect solar energy and provide electricity while saving it as a fuel in the form of hydrogen.
The system that Professor Diale and her colleagues are hoping to introduce is a device that uses solar energy entirely to power all forms of household and industrial uses.
South Africa occupies a position on the world solar map that allows the country access to 4.5 to 6.5 kWh/m2 of solar power per day at 2 500 sunshine hours per year. This is in stark contrast to Germany,
PhD student Kelebogile D Maabong, with Rita Toth, Artur Braun, Jianjun Wang and Debajeet K Bora from Empa.
a country that is at the forefront of solar power
and a world leader in PV installation, yet receives
on average only 3.3 sunshine hours per day. South Africa’s geographic position means that solar energy must be considered as a viable solution to the energy challenges that face the country, and in particular for communities in rural areas and informal settlements. As most of the data in solar energy systems and technologies still come from developed countries, Professor Diale’s goal, and that of her group and collaborators, is to generate South African solar energy collection devices, and data sheets.
Supported by National Research Foundation (NRF), Professor Diale and her team also collaborate with Dr Onesmus Munyati at the University of Zambia, in developing flexible all-polymer solar cells that can
be used as roof-top paint. Metal nanoparticles are embedded in the paint to improve light harvesting. Further collaboration with the University of Dar Es Salaam, led by Dr Margaret Samiji, has enabled the team to produce zinc oxide nanorods, which are used in making solar cells, thereby reducing the cost with easy-to-make metal-oxides. Further collaboration with the Swiss Federal Laboratories for Material Science and Technology (Empa), Switzerland, has enabled her team to use rust (Fe2O3) as an electrode to directly convert solar energy to solar fuel, hydrogen.
In collaboration with Dr Artur Braun in Switzerland, Professor Diale’s team is involved with the direct conversion of solar energy into solar fuels. Using a photoelectrochemical cell for water splitting, rust is used as a semiconductor to collect solar energy, producing electrons and holes in a solution, where water is oxidised to oxygen and hydrogen.
Mmantsae Diale
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