Solar thermal technology, which produces hot water, has become very efficient even in northern climates. Newer versions using evacuated glass tubes are able to supply between 50 and 70 per cent of domestic hot-water needs.
Solar photovoltaic panels, which generate electricity, are currently dogged by high cost, both financially and in terms of the heat energy used to melt the silicon in the cells. Although in most locations in the UK you will still eventually see both an energy and cash payback, neither the economics nor the thermodynamics are as attractive as those for its thermal cousin.
This could be set to change with the arrival of ‘thin-film’ photovoltaics, which use conducting chemicals that can be ‘sprayed’ or ‘printed’ onto glass or plastic backings, avoiding the high-energy processes associated with conventional manufacturing. However, many of the new thin-film technologies rely on heavy metals such as cadmium, or nano-scale particles such as titanium dioxide molecules or carbon nanotubes. If we are to accept the efficiency benefits brought by these technologies, we must make sure that manufacturers have stringent ‘end-of-life’ procedures in place to safely recycle these dangerous compounds.
Another area where the sun’s energy offers huge rewards is in Concentrating Solar Power (CSP). Here, solar radiation is focused using curved or parabolic reflectors onto specially designed surfaces, usually containing molten salts. These salts are then used to boil water, driving steam turbines and producing electricity. Estimates suggest that covering an area of the Sahara desert 254 km by 254 km with CSP plants could provide power equivalent to the entire world demand for electricity. Using high voltage DC power transmission would then allow electricity to be transmitted from North Africa to London with only a 10 per cent energy loss.
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This article first appeared in the Ecologist November 2007