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A sunny future for solar cells
Patenting activity on photovoltaic technology grew phenomenally during the past decade, reflecting the increasing importance of renewable energy sources
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With constantly rising fossil fuel prices, concern about security of energy supply, and growing evidence of climate change induced by society’s carbon dioxide emissions, interest in renewable energy sources has never been more intense.
Besides wind power and advanced biomass technologies, solar power is an increasingly attractive alternative to hydrocarbons power sources.
Now's the time: get ready for solar cells
Life on Earth depends on the Sun for its energy. This steady and reliable source of light and heat supplies up to 1.0 kW of power to every square metre of the planet’s surface. Tapping into that universal energy supply in a clean and economic way has been a goal for energy technologists for many years. Today, it seems that this dream is close to reality.
Photovoltaic (literally light-electricity) technology, also known as Solar Cells, was first developed for space applications in the 1950s. As an energy source, photovoltaic (PV) technology has many advantages – it is modular, clean, easy to maintain, and can be installed almost anywhere, provided a sun-facing surface is available. The electricity produced can be used directly, stored locally or fed into an existing electricity grid.
At the European Patent Office, Alberto Visentin has been monitoring trends in solar energy technology for over twenty years. Based at the organisation’s Berlin office, is the EPO Technology Counsellor for photovoltaic technology. He sees modularity and reliability of PV technology as key features. “A single solar cell module may generate only 50W, but any number of modules can be integrated in a system to create facilities from a few kW up to 10 or 100 MW capacity,” he said. “Connection is easy. Add to the modules an inverter ( a device that converts the Direct Current produced by the cells into Alternated Current), and you have a power plant.”
An extended family of photovoltaic
technologies
Currently, most commercially produced solar cells are based on silicon technologies (1) .
Two of these silicon technologies are based on processes similar to those used for microprocessor fabrication, using high-purity silicon wafers. “On one hand, the most efficient solar cells are produced with monocrystalline silicon, but this material is quite expensive,” says Alberto Visentin. “On the other hand, polycrystalline silicon is less expensive, and less energy is required for its production.”
Alberto Visentin nominated a key patent in crystalline Silicon PV technology for the EPO/European Commission Inventor of the Year Awards (2) in May 2006. The key feature of this patent (3) is a series of contacts buried deep in the Silicon that traps more light-generated carriers and increases the energy conversion efficiency of the cell. The evolution of this cell design, although still too expensive for widespread application, made it possible to produce cells reaching about 25% efficiency. These cells are used for example as the power source for vehicles competing in the World Solar Challenge.
Besides, thin-film silicon technologies have also been developed to place a thin film of amorphous or microcrystalline silicon onto flat large-area substrates such as glass. This has the advantage of allowing the mass production of very large-area PV devices. “These devices are less expensive than conventional PV technology but deliver a lower conversion efficiency of between 5-8%,” Visentin explains. A specific thin-film technology is based on the use of Copper Indium Diselenide (CIS) material. “CIS has the advantages of the silicon thin-film technology but has good efficiency and is not too expensive,” says Visentin. “This technology is quite new on the market but very promising.”
In the background, a major trend in recent years is organic solar cell technology. The efficiency of this technology is still very low, but the organic materials have good potential for very cheap large surface coating and can be used in thin film applications. This would allow for easy integration in buildings – window coatings, for example. In particular, there are two main categories of organic solar cells. The first is dye-sensitised solar cells (DSC) (4) .
A different way to enhance efficiency involves the developments of light-concentrating systems. This involves the use of small surface, highly efficient solar cells based on semiconductor materials such as Gallium Arsenide, coupled to large light gathering devices, such as mirrors or lenses .
Booming demand
The contribution of solar cells amounts only to some 0,1% of the world energy supply, but production and installation of PV technology is growing strongly, at double digit rates. In fact, demand for solar cells is now outstripping the available supply of silicon. “Although silicon is one of the most abundant elements on Earth, pure crystalline silicon, the industry’s feedstock, is in short supply,” says Visentin.
Between 2003 and 2004 the total installed capacity for PV power around the world grew by 42%, reaching a total of 2.6 GW. In 2004, 770 MW of capacity was installed, of which 94% was in three countries – Japan, Germany and the US. These three nations also lead the production of solar cells with Japan producing 604 MW, Germany 198 MW and the US 138 MW.
Production and installation is also taking off rapidly in the emerging economies such as China. “In 2004, Chinese solar cell modules production was estimated to be 65 MW with an installed capacity of about 75 MW,” says Visentin.
The importance of the PV energy sector can be gauged by the presence of oil majors such as Shell and BP, whose solar cell production have reached 6% and 7% of the global market respectively in 2004. However, Japanese electronic companies are the market leaders, with Sharp at 29% and Kyocera at 11%.
Start, sustain, take off
The Japanese market was initially boosted by a generous financial incentive for installing solar cells, and although this subsidy is no longer available, the market is still growing very strongly. “In Europe, and particularly in Germany, the use of feed-in tariffs has helped to grow domestic and commercial use,” says Visentin.
The production of silicon solar cells involves the use of large amounts of energy, and this has led to some questioning of whether it is truly a renewable energy source. But recent work by the University of Utrecht and ECN (5) has calculated the energy payback time for various silicon technologies in European locations. “The calculation estimates the time the solar cell must be in operation before it has generated the amount of energy that was used in producing it,” concludes Visentin. “The results show payback in two to four years.”
Take it for granted: with oil prices staying high, Solar Cells will keep their place in the sun.
From the perspective of patenting
A native of Rome, Alberto Visentin studied for a degree at Rome University, specialising in nuclear physics. He was first introduced to solar energy during two subsequent years at the University of Cosenza, where he was involved with the use of solar technology to produce thermal power. “My experimental work was performed in Rome using parabolic trough reflectors to concentrate the sun’s energy on liquid-filled pipes,” he says. “In mid-summer the liquid in the pipes could reach very high temperatures – up to 300 °C.”
Visentin joined the EPO in January 1980, soon after it had been set up. In 1985, he was appointed into semiconductor technology, working on optoelectronic technology such as photodiodes, light-emitting diodes and solar cells. “The proportion of my work on solar cell applications was relatively low at first,” he observes. “The global number of applications in the field grew steadily over the 1990s to reach just over 1000 first filings in 1997, but by 2002 the number had jumped to over 2000.”, says Alberto Visentin.
In 2003 he was part of the Trilateral Examiner Exchange Programme with the Japanese Patent Office (JPO) and stayed in Tokyo collaborating with Japanese examiners also involved with photovoltaics. “Japan is still the main centre of patenting activity for PV applications with over 70% of first filings for patents between 1990 and 2004,” says Visentin. “I was also able to visit a number of Japanese photovoltaic production facilities.”
In 2003, Visentin transferred to the EPO’s Berlin office, and - dealing almost exclusively with patent applications in the photovoltaic field as a senior expert - he now acts also as Technology Counsellor for the EPO. He is a regular participant at photovoltaic conferences, and has presented papers with latest developments in this filed at the European Photovoltaic conferences in Paris in 2004 and Barcelona in 2005.
“The global number of applications in the field grew steadily over the 1990s to reach just over 1000 first filing in 1997, but by 2002 the number had jumped to over 2000.”, says Visentin
May 2006, Brussels
- Journalist: Tim J Reynolds, European Service Network
- Expert opinion: Alberto Visentin, EPO
- Chart: Henry Lehtiniemi, EPO
- Photo portrait: Erika Valencia, EPO
- Research and coordination: Leo Giannotti, EPO.
References
(1) For example, see WO 02103810
(2) http://www.european-inventor.org
(4) For example, see WO 9116719
(5) M.J. de Wild-Scholten, E.A. Alsema, Environmental Life Cycle Inventory of Crystalline Silicon Photovoltaic Module Production, Proceedings of the Materials Research Society Fall 2005 Meeting, Symposium G, Boston, USA, 28-30, November 2005, online publication at www.mrs.org. MRS Volume 895 (the study cited by the ECN is at: http://www.ecn.nl/nieuws/nieuwsbrief/mei-2006/fotovoltaische-systemen-hebben-een-energieterugverdientijd-van-slechts-17-jaar/)