Solar Energy Perspectives - IEA

Solar Energy Perspectives: Solar photovoltaics
Figure 6.3 The PV learning curve
100
PV module price (USD 2010/Wp)
< 1976
< 1980
10
< 1990
< 2000
LR: 19.3%
< 2010
1
0.1 1
Source: Breyer and Gerlach, 2010.
Key point
10 100 1 000 10 000 100 000
Cumulative capacity (MW)
Figure 6.3
PV has shown a learning curve of 19.3% on average over 34 years.
Crystalline silicon
Current commercial PV technologies are wafer-based crystalline silicon (c-Si) and thin films
(see next section). Crystalline silicon technologies – single-crystalline (sc-Si) or multicrystalline
(mc-Si) – currently dominate the market with an 85% share. Cells are sliced from
ingots or castings, or made from grown ribbons, of highly purified silicon. A potential
junction is created, an anti-reflective coating deposited and metal contacts added. The cells
are then grouped into modules with a transparent glass for the front, a weatherproof material
(usually a thin polymer) for the back, and often a frame around. The back can also be made
of glass to allow light through.
Modules are usually guaranteed for a life-time of 25 to 30 years at minimum 80% of the
rated output. Sc-Si cells show efficiencies – the ratio of electric output over the incoming
solar energy – of 14% to 22%, mc-Si from 12% to 19%. These efficiency levels are usually
given in “standard” conditions, including air mass of 1.5 (distance travelled through the
atmosphere 50% greater than when the sun is exactly overhead) and 25°C external
temperature. But the efficiency of crystalline silicon PV decreases with rising temperature
levels. Crystalline module efficiencies are slightly lower than cell efficiencies. Advanced
manufacturing technologies, such as buried contacts, back contact cells, texturing
processes and sandwiches of crystalline and thin films promise increases in efficiency.
Although c-Si cells represent the most mature PV technology, there is still room for
improvement. Important aims are to further reduce the thickness of cells to bring the use of
costly highly-purified silicon significantly below 5 g/W; to reduce the energy and labour costs
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