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  New horizons in research funding: Developing junior academics and enhancing research support for humanities and social sciences

  Reorganization of RGC Subject Panels

  Liquid-based Photovoltaic/Thermal Cogeneration for Real Building Application

  Development and Study of Hybrid Photovoltaic Cells

  Interfaces between Fullerenes and Semiconductor Nanowires: Nanofabrication and Photoinduced Charge Separation

  Vagus Nerve Stimulation Therapy: 
A New Tool for Suppressing Visceral Pain

  On the Architecture of Synapses

  Unlocking the Causes of Stroke in Asia: The Importance of Intracranial Atherosclerosis

  Area of Excellence in Information Technology

  RGC Collaborative Research Fund – Layman Summaries of Projects Funded in 2010/11 Exercise

Hong Kong, a modern sub-tropical city, has a great potential of applying solar energy in hotwater and electricity cogeneration. Most buildings here are provided with conventional gas/electrical water heaters for serving hot-water supply. According to the energy end-use data (2010) published by the Hong Kong Government, direct hot water production consumes about 5% of the total energy use in the city, and 20% when considering only the domestic sector. Since 2005, the Hong Kong Government has been targeting at 2012, with 1-2% of the territory-wide energy use from renewable energy sources. On the other hand, direct electricity generation from photovoltaic (PV) is more expensive than conventional power generation. The situation is expected to remain for some years.

By integrating PV modules with solar water heating collectors, the increased energy yield per unit collector area is able to shorten the economical payback period to less than 1/4 of the plain PV application. Such photovoltaic/water-heating (PVW) cogeneration is found to be much promising than the separate side-by-side installations of PV modules and solar thermal collectors from energy conversion, space utilization, and aesthetic points of view. The rationale behind the integration is that a PV cell available in the commercial market converts solar radiation to electrical energy with a peak efficiency in the range of 6-15%, depending on the specific PV-cell type in use. Most of the incident solarenergy is converted as heat, leading to an increase in the cell working temperature. By cooling the PV module with a stream of water, the electricity yield can be improved. In many places including Hong Kong, the promoted use of renewable energy has become a long-term government policy. With more and more solar systems required to be installed in buildings, the available roof space and facade surface area will sooner or later become inadequate for the wider application of solar energy. The hybrid PVW collector thus has a market potential to become a popular commercial product.





Dr Tin-tai Chow and the photovoltaic/ water-heating cogeneration system

An escalating number of research activities on PVW has been reported in the last few years. But so far the literatures were reporting the numerical or experimental findings, with inadequate coverage on real plant operation and system reliability. The international research community has placed real project demonstration with longer-term monitoring as a current strategic need of the technology. 

Accordingly, a PVW system has been constructed to serve an office building at our Kowloon Tong campus. The warm water generated is to serve a selected number of pantries as tap-water source for general use.

The electricity generated from the polycrystalline silicon solar cells is to support the power supply to a group of EXIT signs of the building. The working experiences gained from this small-scale PVW system is to provide practical information for improving the engineering design and installation of future hybrid PVW systems in buildings. The field measured data will be analyzed from energy saving, sustainability, reliability and finance aspects, as compared to the conventional or alternative design options in Hong Kong.

Dr Tin-tai CHOW
Division of Building Science and Technology
City University of Hong Kong