Can thin film really beat crystalline silicon technology?
Last week MNRE has released the generation data of solar projects operating under NVVN and it is clearly visible that the energy yield from the projects which has used thin film technology is about 10-15% higher as compared projects of crystalline silicon technologies. Adoption of thin film technologies for utility scale plants started in the NVVN projects as the thin film modules imported while a project which has to use crystalline silicon module it has to be resourced purely from the domestic suppliers as part of NVVN guidelines. Most of the NVVN projects adopted first solar modules and there was lot of criticism about thin film technology and now when the generation figures from thin film technologies are better it gives comfort to project developers in selecting thin film technology. Recently Mahindra EPC has signed an MOU with First solar and most of their upcoming plants will be using first solar modules.
Increased efficiency and cheaper material are the two factors, which have made thin film technology price competitive has compared to traditional crystalline silicon technologies. The cost of thin film modules is still about 10% higher as compared to crystalline silicon modules but we believe that in future the price reduction potential is huge in thin film technologies. Recently first solar announced that there modules at 36 cents per Watt by 2017.
Recently IBM has introduced solar cells which are made from copper based material and has the advantage that the cells can be meet typical inexpensive ink based process. The thin film technology has in major categories which comprise of CIGS (Cadmium indium gallium selenide) and CdTe technology .While CdTe technology is by first solar in market the CIGS technology is led by solar frontier from japan. Efficiency in these modules have reached about 12-13%. Which has made crystalline silicon technologies vulnerable in terms of their existence and survival in price war
Another advantage of thin film technology is their temp coefficient which is about -0.2%/⁰C as compared to typical crystalline of-0.5%/⁰C.This makes thin film attractive and sustainable to operate in high ambient Indian temperature conditions. Typically thin film modules are frameless and semiconductor material is sandwiched between glass which leads to lower cost and light weight. The lower temperature coefficient of thin film modules makes it easier in terms of inverter compatibility and string size can be designed in a such a way that the output voltage remain within the range of inverter input window.
As thin film module are frameless it requires special clips and structures so that the mechanical stress-thermal stress on the structure do not cause module breakages. The DC wiring in case of thin film module will require more number of circuit combiner Box as compared to typical crystalline silicon modules. Overall if we are selecting thin film modules we have to consider about 20% more space for a given project size as compared to crystalline silicon modules.
It is expected that considering the fact that crystalline silicon modules manufactures do not have any further scope for price reduction and recent price fall of crystalline silicon was because of oversupply. It is expected that thin film technologies may lead the market in future. Some of the companies such as SANYO as come up with a technology which is hybrid of crystalline silicon and thin film technology known as Herto junction features and technologies which combine the features of crystalline and thin film will absorb wider spectrum of solar radiation. As highlighted by first solar if we get PV modules at 36 cents/W solar PV will surely reach to grid parity and the growth of the sector will be not be constrained by the policies.
Dr Sanjay Vashishtha & Rishikesh Muthyal