The School of Engineering hosted a seminar by Dr Christos Markides of the Imperial College in London who addressed the topic: High-Performance Distributed Solar and Low-Grade Heat Conversion Technologies: Challenges and Opportunities.
Markides said solar energy could be used to provide either heat or electricity, although most solar panels were designed for one of these purposes. ‘Photovoltaic (PV) panels are the fastest growing solar energy technology, however, they are typically less than 20% efficient in converting sunlight into electricity. Furthermore, PV cells experience a deterioration in efficiency when operated at high temperatures. Hybrid PV-thermal (PV/T) solar collector technology combines PV cells with a contacting flow of a cooling gas or liquid, and offers some advantages when space is at a premium and there is demand for both heat and power,’ said Markides.
‘A major motivation in PV/T technology is to cool the cells to increase their electrical efficiency, while delivering useful thermal output. PV/T technology is highly efficient, capable of achieving combined system efficiencies potentially in excess of 70%. The most common use of the thermal output from PV/T systems is to provide hot water at 50-60°C. However, a much wider range of opportunities arises at higher temperatures, where power-generation cycles or cooling technologies can be combined with PV/T collectors. These options become viable at temperatures typically above 80°C, with efficiency progressively improving at higher temperatures,’ he said.
‘Operating PV/T collectors efficiently at high temperatures is a significant challenge, however, since thermal losses that result in a drop in collector performance are exacerbated at higher temperatures.’
Markides also spoke on recent advances in evacuated PV/T technology combined with organic Rankine cycle power systems for high-efficiency electricity generation.
A lecturer at UKZN’s School of Mechanical Engineering and leader of the Group for Solar Energy Thermodynamics (GSET), Mr Jean Pitot, was instrumental in organising the seminar. ‘It was a pleasure to have the opportunity to host Dr Markides, and to hear more from him regarding solar energy and waste heat utilisation research being undertaken at Imperial College’s Clean Energy Processes laboratory. ‘The global energy landscape is changing rapidly and technologies such as those his group is studying have the potential to profoundly contribute towards the common goal of generating cleaner, cheaper and more accessible power,’ said Pitot.
Markides has BA, MEng, MA and PhD degrees in energy technologies, obtained from the University of Cambridge in England. He also has technology transfer experience as co-founder of multiple spin-out companies. He holds the post of Head of the Clean Energy Processes (CEP) Laboratory at Imperial College.
Words: Prashina Budree