Page 70 - Applied Photovoltaics
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Chapter
4
CELL PROPERTIES
AND DESIGN
4.1 EFFICIENCIES
Under laboratory conditions, with current state-of-the-art technology, it is possible to
produce single-crystal silicon solar cells with efficiencies in excess of 24%. However,
commercially mass-produced cells are typically only 13–14% efficient. There are
many reasons for this; the over-riding one being that, while efficiency can be the
major aim for laboratory produced cells, irrespective of cost, complexity of
processing or throughput, in general, laboratory techniques are unsuited to industry.
Solar cell research continues to improve the efficiency of cells towards the currently
accepted theoretical limit of about 30%. Commercial products lag some years behind
laboratory results, but commercial module efficiencies of over 20% could be see in
coming years. Higher efficiency makes a dramatic difference to the cost of
photovoltaics as an electricity source, since fewer modules are required for a given
power output. The cost of electricity generated by a photovoltaic system therefore
depends on its initial cost, operating life, operating costs and electricity output, as
well as the costs of borrowing money and the rate at which current monetary values
are discounted over time. These factors can be represented by a standard economic
discounted cash flow equation:
