The two main categories of solar technology are defined by the choice of the semiconductor, either crystalline silicon (C-Si) in a wafer form or thin-films of materials such as amorphous silicon (A-Si), cadmium telluride (CdTe), or copper indium gallium selenide (CIS/CIGS).
Crystalline silicon has been around for over 35 years and accounts for about 85 per cent of the global market and crystalline silicon modules are of two types, monocrystalline and multi-crystalline.
The argument favouring A-Si thin-films when they emerged in 2000s was that it used a fraction of polysilicon compared to crystalline silicon and since polysilicon was expensive then (around $600/kg), A-Si was seen as the technology of the future which would help bring down the cost, close to grid parity. However, the trouble with A-Si was the high degradation of thin film (~1.5 per cent pa) and the low efficiency (six to eight per cent). Due to developments in the global market, polysilicon prices have fallen and today it is available at around $60/kg. So the economic argument in favour of thin-film has lost its validity. On the other hand, the problem of low efficiency and high degradation has not been solved. Their low efficiency means the system requires roughly double the space and correspondingly the cost of the balance of systems (inverters, fixtures, etc) goes up. This more or less balances out the initial lower cost of thin-film modules as compared to a C-Si module.
According to a Lux Research report, advances in crystalline silicon and the falling cost of polysilicon have only increased pressure on manufacturers of emerging thin-film technologies to improve margins or face extinction. Their low efficiency and cost-effectiveness is not competitive at present. So competing with electricity cost generated through conventional sources of energy is currently not possible for thin-film manufacturers. Coupled with this, banks and manufacturers shy away from financing thin-film in favour of more mature and abundant crystalline silicon modules for projects in 2011, which may continue in the coming future, resulting in narrowing the thin-film expansion.
CIGS technology is getting more popular than other thin-film technologies due to higher efficiency and reduced manufacturing costs. From 2010, this segment is expected to capture the maximum share in the thin film module market.
The author Natarajan Mani is Additional General Manager at Tata BP Solar. Views are personal.