IT WAS IN 1839 that Antoine-César discovered the photovoltaic (PV) effect, while experimenting with a solid electrode in an electrolyte solution.
The first commercial applications of this discovery were seen only in the 1930s, when selenium or copper oxide cells were employed as photometers in photography.
The silicon solar cell was then developed by Russell Ohl in 1941 and first demonstrated conversion efficiency exceeding 1% and soon after, exceeded 6%. By the late 1980s, 20% efficiency had been exceeded and in 1989 a concentrator solar cell achieved an efficiency
Evolution has been swift since then too. Today solar energy is gaining recognition as the leading alternative energy source for the 21st century, with analysts predicting that the contribution of solar energy to world supply will grow from 0.3% to 15% over the next five years.
Three generations of history
First generation solar cells are made of crystalline silicon and are manufactured using process technology developed from the extensive knowledge base of the microelectronics industry.
Despite the relatively poor light absorbance of silicon, large area, high quality, stable cells capable of converting up to 16% the absorbed light energy are produced and these still dominate with over 80% market share.
The achilles heel of this technology however, has always been the volume and therefore cost of the high purity silicon required for construction.
Despite the extensive use of ‘off-spec’ recycled silicon material, it contributes 40-50% of the cost of a complete photovoltaic module.
Continued research and optimisation has produced single junction silicon devices that approach the theoretical limiting efficiency of 33% and claim cost parity with fossil fuel energy generation, after a pay-back period of less than four years.
Second generation technology was developed specifically to avoid the high energy consumption and cost of silicon wafer material, but at the expense of inherently lower energy conversion efficiency rates.
Crystalline silicon is replaced by semiconductor materials which, due to their strong light absorbing properties, require a layer only micrometres thick and including; amorphous silicon, cadmium telluride and copper indium (gallium) di-selenide.
It’s suggested in some quarters that while it takes 80 cents worth of silicon to generate 1 watt of electric power using 1st generation cells, only a penny’s worth of these semiconductor materials can do the same job.
Manufacturing techniques like vapour deposition, electroplating and the application of ultrasonic nozzles have the advantage of reduced high temperature processing and therefore lower energy consumption.
As a result of the complexity of thin-film technologies, the challenge of developing manufacturing processes that produce cells of consistent quality and performance has been huge – and required major corporate backing for over 20 years.
Thin-film technologies now offer pay-back times in the range of 1-1.5 years and this equates to Energy Returned on Energy Invested (EROEI) ratios between 10-30, given their lifetime of at least 30 years.
Because of their attractive price-to-performance characteristics, thin-film modules are expected to gain 50% market share as soon as 2012.
Third generation technologies meanwhile, aim to enhance the weaker electrical performance of second generation cells, without compromising their low production costs.
Techniques such as adopting multi-junction cells, or the concentration of incident spectrum are expected to allow the theoretical solar conversion efficiency limit to be exceeded. Currently performance targets are in the range 30-60%.
Concentrators that employ mirrors or lenses to concentrate the light on to specially designed PV cells have been shown to boost conversion efficiency close to 40%, but have not yet been widely adopted.
The concentration of solar radiation significantly increases operating temperatures and therefore cooling is required to maintain efficient cell functioning. This technology is inoperable under cloudy skies and also requires tracking mechanisms to follow the daily and seasonal movement of the Sun’s incident radiation.
Electrochemical PV cells that have a liquid phase active component are a cheap and therefore attractive alternative form of PV cells, also known as Dye Solar Cells (DSCs).
Semi-transparent, they could be applied to building glass to provide shade and generate power simultaneously.
Strategic role of the gases industry
The production of solar cells requires large volumes of ultra-pure industrial gases and with annual growth rates averaging 48% over the past decade, the PV industry represents a significant growth market for industrial gases.
As manufacturers of photovoltaic devices scale up production, in order to drive down the unit cost of production in pursuit of the industry goal of less than $1/Watt, their total demand for gases can be expected to grow rapidly.
Recent growth estimates suggest that solar applications could double the volume of silane already required for the production of semiconductors and Liquid Crystal Displays (LCDs).
Other gases critical to the expansion of production volumes include nitrogen, argon, helium, hydrogen, nitrogen trifluoride, and fluorine.
The future impact of this anticipated demand is great enough to require strategic investments and specific long term contracts on the part of the major industrial gas suppliers.
Anish Tolia, Market Development/Solar for Linde Electronics, recently warned attendees at the Thin-film solar summit in San Francisco that gas technology can significantly impact their production cost per Watt. Under the restraints of traditional gas supply business models, the cost reduction targets necessary for PV energy to compete effectively seem unattainable.
March 2009 saw The Linde Group awarded the long-term contract to supply all gases, storage and distribution systems and on-site gas management services to two new next-generation thin-film manufacturing facilities owned by Masdar PV – subsidiary of the Mubadala Development Company of Abu Dhabi.
Linde, a major supplier to solar module manufacturers in key markets like Germany, Spain, Italy, China, Taiwan and India, has already partnered customers on projects with a total target capacity of more than 1GW peak capacity per annum.
Air Liquide plans to invest over $20m to fulfil several new long-term supply contracts with some of the world’s largest solar cell producers, which will complement the group’s leadership position in the PV market in Germany and Japan.
In Eastern China too, Air Liquide will provide turnkey gas solutions to new thin-film PV facilities boasting target production of over 300 MW peak.
In Greece, Helio Sphera has selected Air liquide to supply its new site while in the Philippines, leading manufacturer Sunpower has expanded its contractual requirements to include their Fab2 investment, with an output target of 300 MW peak of crystalline silicon PV units.
Air Products recently secured a long-term supply agreement with China’s Best Solar Hi Tech Co., Ltd. for bulk and speciality gas supply and systems at the company’s new thin-film PV facility, with planned annual capacity of 330MW peak.
Taiwan-based Green Energy Technology recently selected Air Products as well, as gas supply partner for its new amorphous-silicon thin-film PV production facility in Taoyuan.
Equipped to produce 5.7m2 panels, it is scheduled to achieve annual capacity of 30 MW peak during 2009 and ultimately 50 MW by year end. During 2008 alone, Air Products secured over 20 new PV supply contracts in Asia, such is both the demand from this region and the US gas major’s expertise in this field.
During the past decade there has been a worldwide realisation that unless something is done to arrest the long predicted and now measurable effects of fossil-fuelled energy production, our Earthly home will be rendered uninhabitable.
Several governments have moved to implement surcharges on the emission of carbon dioxide and in response, power utilities have introduced financial incentives that encourage consumers to invest in renewable electricity – and reduce dependence on grid power.
Going into 2009, Germany leads the world in terms of installed PV capacity and the US ranks fourth, behind Japan and Spain who achieved a phenomenally fast growth rate of 285% in 2008.
Last year Japan saw positive demand growth for the first time since 2005 and the market potential of the US began to emerge. Energy policies in Italy, Australia, South Korea, France, India, Portugal and Israel are stimulating similar tends.
The high cost of generation one PV modules strongly inhibited the initial adoption of solar energy, but efficiency gains in manufacturing and the cost benefits of increasing production volumes have resulted in steadily declining prices.
The cost of financing installations significantly extends the pay-back period however, and has weakened demand for PV modules.
This young ‘sunshine’ industry that has enjoyed a decade of annual revenue growth above 35% has been hard hit by the recent contraction of available finance.
The most optimistic growth estimate for 2009 is 13%, forcing manufacturers to cut prices, and this is predicted to result in the price of PV modules falling to $2.50 per Watt in 2009 and $2.00 per Watt in 2010.
This will certainly hasten the achievement of cost parity with grid power in many countries, with massive implications for future demand.