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Coal has large carbon footprint


I refer to the article (“Dirty reality behind solar power”, September 10) and the subsequent clarification (September 16).

It was asserted that the energy produced from burning coal directly is more than the energy generated by a polysilicon solar panel manufactured by using the same amount of coal.

This way of comparing different methods of electricity generation is incomplete as it does not compute the carbon footprints of the two methods of electricity generation. A more commonly accepted way of making such comparisons among the international science community is to make reference to the life cycle of CO2 emissions of different electricity generation systems. This is known as the life cycle inventory analysis.

The technical details are contained in the note entitled “Carbon footprint of electricity generation” published by Britain’s Parliamentary Office of Science and Technology. Carbon footprint is defined as “the total amount of CO2 and other greenhouse gases emitted over the full life cycle of a process or product, expressed as grams of CO2 equivalent per kilowatt hour of generation”.

All electricity generation technologies emit CO2 at some point during their life cycle. None are entirely carbon free. However, according to the “life cycle inventory analysis”, published in October 2006, the conventional coal combustion electricity generation system in Britain had the largest carbon footprint, more than 15 times that of a solar energy electricity generation system (the British photovoltaic, PV, power systems using crystalline silicon). Furthermore, the carbon footprint of PV cells would be reduced with thin-film technologies using less silicon and other new semi-conducting materials.

Different thin-film PV technologies are active areas of applied research supported by the Innovation and Technology Commission, conducted at the Nanotechnology and Advanced Materials Research and Development Centre in Hong Kong.

Yue On-ching, science adviser, Innovation and Technology Commission

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