Attaining grid parity

Attaining grid parity

In addition to consuming a lot of expensive silicon the traditional wafer route is also labor intensive as it requires quite a bit of wiring and mechanical assembly (which is why most modules by this route are now assembled in China and some even in Bangalore). So, another thrust in reducing the cost of solar modules is to design them to require minimal assembly, the same idea that led to the spectacular success of integrated circuits. To this end continuous roll to roll processes have been developed and put into production, the leading example of which today is the technology developed and used by United Solar (Michigan, USA) to deposit thin films of silicon and silicon-germanium alloys on sheets of stainless steel.

What would come as a surprise to most Indians today is that this technology had its genesis in Calcutta and United Solar of USA is led by Dr. Subhendu Guha with a PhD from Calcutta University!

Compared to the traditional thick silicon wafer solar cells, thin film solar cells consume much less precious semiconductor material and on a per watt basis cost only 60-70 percent as much.

At present, First Solar Corp. of Phoenix AZ, USA, the world's largest thin film solar cell company, uses its proprietary cadmium telluride thin film technology to deposit solar cells on glass sheets and claims the lowest cost in the world ( $ 1.25 per watt ). They will soon ramp their production from 300 MW py to 1 GW py. However, be it silicon or non-silicon ( like Cd Te or CIGS ), in the absolute efficiency scale thin film cells in production are somewhat deficient as due to various unavoidable imperfections in crystal structure, their solar conversion efficiency, seldom exceeds 10 percent, less than half that of the best silicon wafer solar modules.

The production processes are also more sophisticated and thus cost more (turnkey plants made by Applied Materials for thin film silicon cells on glass sheets may cost over 3 million USD per MW py capacity). APSTL, the authors company in Scottsdale, AZ, is developing silicon PV cells that will consume only a fraction as much polysilicon as the traditional wafers yet have conversion efficiencies well above that of thin film cells.

The highest solar conversion efficiency today is produced by cells made of multi-junction compound semiconductors. Spectrolab, located north of LA, makes cells that show efficiency of up to 40 percent (nearly double that of the best silicon wafer cells).

However, due to the slow and exact process used to grow these semiconductors they are extremely expensive ($2/sq. mm of die ) and most frequently can be used only for defense and satellite applications. Mars lander robots, including the one that recently confirmed water in Mars, use these multi-junction solar cells to generate enough electricity to operate a power shovel to dig into the hard Martian soil or run a whole chemistry lab on board!

To make these very expensive multijunction solar cells affordable for commercial applications they need to be integrated with concentrator optics (mirrors with cassegrain optics) with attendant cooling systems as well as sun-tracking devices.

Maintaining competitiveness in Indian solar/PV
The above thumbnail sketch should be enough to convince both government policymakers and entrepreneurs that solar PV is an industry deeply rooted in physics and hardcore sciences and it is no place for those with software/design background to dabble in and mess up.

The long term goal should be to identify strategies to maintain competitiveness in the nascent solar PV industry in India even if to get itself off the ground it first uses standard off the shelf tools and technologies that are available to competitors, e.g., China etc. too.

This requires a policy of continuous improvement in cost and/or performance via technology, to sustain, which requires a capable domestic R&D and hardware base. To this end the government ministries must formulate policies that are well grounded in the technical and business realities of the semiconductor industry worldwide as well as adopt a systems approach. That is, it is not just offering financial incentives to set up semiconductor plants, but simultaneously, finance the development of the missing technical infrastructure for semiconductors, viz training of manpower in physics, materials sciences and construction of semiconductor production and testing equipment.

Research based training/education programs on solar photovoltaics and alternative energy in general should be launched at select Indian universities.

Lastly, a new Semiconductor Hardware Association of India, composed primarily of physicists and hardware engineers (rather than the unqualified software/design type pretenders who have contributed to the wafer fab fiasco), should be created at the earliest so as to co-ordinate the development of the semiconductor hardware manufacturing industry in India with minimum avoidable delays.

The author is the Chief Technical Officer of APSTL llc, of Scottsdale, AZ, USA, a company that specializes in developing key semiconductor technologies and licensing them worldwide.