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FEATURE PHOTOVOLTAICS


HERE COMES THE


Greg Blackman and Rob Coppinger on how laser technology, and infrared/ thermal imaging, can maximise the efficiency of solar energy


SUN


According to the European Photovoltaics Industry Association (EPIA), cumulative PV installations – which reached 100GW in 2012 – could grow to more than 400GW by 2017.


While the supply of PV modules exceeds demand at the moment, analysts at Lux Research predict that supply and demand will balance out by 2015. They predict a 10.5 per cent compound annual growth rate to $155 billion by 2018 – good news for companies supplying equipment for the solar market, including machine vision firms installing inspection systems for quality control. The construction of solar panels – each panel is made of a number of solar cells, which, in turn,


8 PHOTONICS FOR RENEWABLE ENERGY 2013


are comprised of a number of silicon wafers, all connected in series – means their efficiency relies on every wafer and cell working fully. ‘Manufacturers want to match and characterise


each cell precisely, so all cells within a panel generate the same amount of electricity,’ says Dr Jean-Edouard Communal, regional sales manager at Raptor Photonics. ‘The efficiency of the overall panel will be determined by the least efficient cell.’ Raptor Photonics provides cameras for the solar industry, including InGaAs and EMCCD variants for luminescence measurements. Machine vision is used for standard dimensional inspection and defect detection in PV production, but luminescence is more specific to solar cells and can determine the efficiency of a cell or module. The properties of solar panels mean they can be induced to emit light when excited by a burst of light (photoluminescence) or when a current is passed through them (electroluminescence). A small fraction of photo-generated electrons will recombine with a hole to emit a photon in photoluminescence, while a forward biased solar cell will essentially act as an inefficient LED in electroluminescence.


In both cases, the fewer the defects the higher the emission intensity from the wafer, cell, or panel. This makes luminescence measurements an


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