Q&A
July 28, 2008

UNSW's Martin Green

Energy Research News Editor Eric Smalley carried out an email conversation over the past two weeks with Martin Green, a professor of electrical engineering at the University of New South Wales in Australia.

Green is one of the world's leading photovoltaics researchers. He's Executive Research Director of the Australian Research Council's Photovoltaic Centre of Excellence. He's also a director of CSG Solar, a company that is commercializing UNSW's thin-film, polycrystalline-silicon-on-glass solar cell technology.

Green's research group pioneered the development of high efficiency silicon solar cells. He is the author of six books on solar cells.

Green's awards include 1999 Australia Prize, the 2002 Right Livelihood Award, the 2004 World Technology Award for Energy and the 2007 SolarWorld Einstein Award. He's one of the Australian government's Federation Fellows, and is one of UNSW's Scientia Professors, who are noted for outstanding research.

Green earned bachelor's and master's degrees in engineering from the University of Queensland in 1970 and 1971 respectively, and a doctorate from McMaster University in Canada in 1974.

ERN: What are the important or significant trends you see in energy research?

MG: The most significant trends in energy research are clearly towards the development of less carbon-intensive energy supply. They range from reducing the carbon intensity of present supply options to the development of sustainable long-term options such as photovoltaics, on which I am working.

ERN: What would you like to see happen? Is this different from today’s research priorities?

MG: I think developed countries have to more actively use their wealth and resources to get sustainable technology on the market quickly and make it available to the less developed. Germany is a good example of how this can be done. This is not altruism. We share this planet and if growth in the developing world continues to be fuelled by carbon intensive technologies, we all will suffer.

ERN: What is the general focus of your research, and how does it relate to energy?

MG: My research involves improving the performance and economics of solar energy conversion to electricity using photovoltaics. This is generally agreed to be the most desirable of the few options that have been identified for sustainable long-term energy supply. Solar cells generate electricity, with electricity accounting for about one-third of the world’s energy use. This fraction is expected to increase over this century.

ERN: Australia is a natural place to develop solar technologies. How is government support for solar research there, and how does it compare to Europe and Japan?

MG: Our group has been well funded by Australian standards but not because we are working on solar energy. Our support comes from the academic credentials we have generated by our history of world-first results. Even so, funding levels are low compared to Europe and Japan but our research productivity has been high. Regrettably, Australian government support for market development has been almost non-existent while Japan and Europe, particularly Germany, have led the world in this area.

ERN: What is “buried contact” solar cell technology?

MG: Our group produced the world’s first 20% efficient silicon cell in 1985, achieving the “four minute mile” of the solar field (20% of incident sunlight converted into electricity). The “buried contact” cell was the result of our attempt to develop a low cost commercial product based on this work (contacts are buried in the cell surface, rather than lying flat across it). BP Solar was our most successful licensee, with over $1 billion in sales to date. Their “Saturn” module, which uses this technology, was the most efficient solar module on the market during the 1990s. Even now, it is still amongst the best.

ERN: I’ve heard the argument that if photovoltaics cost nothing, electricity generated form solar cells would still be more expensive than today’s grid electricity. With so much research emphasis on solar cells themselves, is there a danger that the ancillary components of solar electricity – the inverters and other electronics – will become a bottleneck?

MG: The thing that needs to be remembered about photovoltaics is that costs have reduced considerably over the last two decades and are expected to reduce further over the next two. The other important fact is that, unlike most other supply options, photovoltaics can be installed right at the point of use. The electricity is much more valuable here than at the output of a large conventional power station, miles from anywhere. For example, a Tier 5 electricity customer in California, presently paying 37 cents a unit (and going up) would not agree that grid electricity is cheap. Photovoltaics is already a cheaper option in situations like this.

I would see inverter and installation technologies as earlier in the learning curve than the cell technology itself and having at least as much to gain from larger volume production, new ideas, more players in the field, and so on.

ERN: What are the milestones in solar cell research on the road to cost competitive technologies, and what is the price point you’re looking for?

MG: Solar cells have been cost competitive in some applications, such as outback power supplies, for more than twenty years. What has happened since then is that the range of economic applications has increased. This is why market development programs are particularly appropriate for photovoltaics. These accelerate cost reduction by opening up new market areas earlier than would otherwise be possible.

Photovoltaics is expected to be competitive with residential grid supply across most of Europe by 2015. The long-term challenge is to bring costs to the level where the technology can compete not only in the retail markets but also in the wholesale bulk electricity markets.

ERN: Photovoltaics research is proceeding along several avenues: dye-sensitized, organic semiconductor, thin-film, multijunction and variations of these involving nanotechnology. What do you like about these technologies, and which have the most commercial potential?

MG: Most present product is based on silicon wafers, similar to those used in microelectronics but a lot thinner. This technology is improving rapidly and will remain the workhorse of the industry for the next decade. I see the evolution past then in two stages. “Second generation” thin-film technology, where the photoactive material is deposited as a thin layer onto a supporting glass substrate, will steadily gain market share over this period. This will morph into a “third generation” of technology, also thin-film, but distinguished by much higher efficiency and the use of abundant, non-toxic, durable materials. This “third generation” will possibly use nanotechnology to allow implementation of advanced cell concepts.

Organic and dye-sensitised cells seem to have a definite future in consumer products, such as mobile telephone chargers. However, significant progress is required to meet the efficiency and durability demands of the bulk power market and it is still uncertain whether they will be able to compete here. Multijunctions, where cells responding to different colour bands in sunlight are stacked on top of one another, have two possible futures. One is in low-cost, “third-generation” thin-film cells. The other is using wafers from other material, much more expensive than silicon, but with the high costs mitigated by concentrating or focussing sunlight onto small-area cells.

ERN: Tell me about your work on these second and third generation technologies.

MG: Thin films are the future, but not if they depend on toxic or scarce or difficult to deposit and unstable materials as most do at present. However, this need not be the case. Witness the 'crystalline silicon on glass' (CSG) technology developed by our group specifically to avoid the triple pitfall above and now available commercially through CSG Solar. Multijunctions are one way of boosting cell efficiency appreciably, the key to the long-term viability of PV.

We developed a unique 'cystalline silicon on glass' (CSG) second generation technology from scratch to overcome limitations in the above areas of the three mainstream thin-films. In the third generation area, we are developing all-silicon cells using silicon quantum dots to control silicon's bandgap. Also, 'hot carrier' cells seem like the long term 'ultimate' PV technology.

ERN: What are hot carrier cells?

MG: A solar absorber has a bandgap or energy threshold. Only photons of energy higher than this creates free carriers. Those of enegy below pass through, those above are absorbed but quickly lose any energy above the gap as heat. This means there is an optimum bandgap for solar conversion (silicon is at the low edge of the range, CdTe is at the upper edge).

In a hot carrier cell, cells are designed to prevent the loss of energy above the bandgap, giving about double the efficiency in principle. We are still working out how to do this but it seems technically feasible (a lot easier than controlled nuclear fusion or quantum computing, for example).

ERN: Solar concentrator technologies, for both solar thermal and photovoltaics, are starting to take off, particularly as the costs of reflectors and heliostats come down. How useful are concentrators for photovoltaics?

MG: Concentrating the sunlight allows potentially low electricity prices even when solar cell prices are high. The problem has been that this approach negates some of the best features of standard photovoltaics. These are the ability to install just about anywhere in small systems that use no moving parts, are very tolerant to dust and dirt and come with a 25 year warranty. However, with multijunction cells now giving over 40% efficiency, concentrating photovoltaics is very competitive in large systems compared to solar thermal electric options, such as those based on Stirling engines.

ERN: A lot of solar energy startup companies seem to the focusing on utility scale electricity generation. Is solar cell technology better suited to centralized or distributed generation, or can we have it both ways?

MG: I think photovoltaics can have it both ways. It is obviously ideally suited for distributed generation. However, “second generation” thin-films are now demonstrating appreciably lower manufacturing costs that are making them increasingly attractive for large centralised plant. Siting flexibility, low overhead and maintenance costs and low water requirements are attractions of such plant.

ERN: What are the important social questions related to energy?

MG: I think the important social issue related to energy is equitable global access to clean energy. Not only Australia, but I believe the entire world, is benefiting from the impressive growth of China’s economy. However, this growth is being fuelled by the construction of new coal-fired power stations at an alarming rate. China is building these since it can source most components very cheaply locally. I think China needs to be able to build the best of more sustainable technology locally and cheaply for things to change. How this can be achieved while providing equitable returns to the developers of such technology is, to me, an unresolved issue.

ERN: What are your thoughts on the state of public understanding of energy and energy research?

MG: I talk around the world on energy, often to-non-specialists, and find the public generally well informed. I think the rise of the Internet and the extreme range of views found there possibly forces the individual to be more discriminating than when books, after some type of review, were the main source of information.

ERN: What could be done to improve the pursuit of energy research in terms of business trends, politics, and/or social trends?

MG: I think a healthy industry is the key to research progress as it provides a mechanism for new ideas to see the light of day. Market development programs, particularly in Germany, have resulted in a spectacular boom in the photovoltaics industry which is seeing more new technology adopted over recent years than in the previous 20 years.

ERN: In a perfect world how would we get our electricity?

MG: The German Advisory Council on Global Change (WBGU) addressed this question in their 2003 report on “Energy in Transition”. Their “exemplary transition scenario” involved 25% of all the world’s primary energy, not only electricity, being supplied by solar electricity by 2050 with 64% supplied by 2100. This is what they believed was technically, if not politically, feasible.

ERN: In terms of energy and anything affected by energy, what will be different about our world in five years? In 10? In 20?

MG: I think in five years, we will see more co-ordinated international efforts to address carbon emission and global warming. Within 10 years, we will start seeing changes in the way electricity is generated and in the types of vehicles we drive, particularly in relation to their fuel efficiency. A period of 20 years is long enough to start seeing major technology shifts.

ERN: What do you imagine you will be working on in five years? 10 years?

MG: In 5 years, I expect that the “second generation” silicon-on-glass technology I have helped develop will be reaching market maturity. In 10 years, I am hoping that some of our “third generation” technology will be ready for commercialisation.

ERN: What got you interested in science and technology?

MG: A superb but eccentric high school science teacher, “Pud” Heenan.

ERN: What's the most important piece of advice you can give to a child who shows interest in science and technology?

MG: Honestly, I have never met a child who has expressed an interest to me in science and technology although others in our group give talks at primary and secondary schools. Our group has been involved in organising model solar car and boat races which gives an outlet for youngsters with technical and science interests. I know some of these have ended gaining doctorates with us in the solar field.

ERN: What's the most important piece of advice you can give to a college student who shows interest in science and technology?

MG: Unfortunately, I don’t have any magic recipe here. I have supervised dozens of students, several of whom have become leaders in academia or industry, so I am probably doing something right. I see my role as being to create opportunities for skills, talents and interests of my students to come to the fore. I am not adverse to giving advice, but usually only when asked and on quite specific issues.

ERN: What books that have some connection to science or technology have impressed you in some way, and why?

MG: I read almost all of Bertrand Russell’s published work in my early years at University. He was a clearly intelligent man, at least as good a scientist as myself, who had spent his life trying to understand life’s important questions. After reviewing the entire history of western philosophy and conducting his own first-principle enquiries over an exceeding long and fruitful life, the end result was that no-one really knew anything, at least on my reading. I think this gave me confidence in trusting my own judgement that has since stood me in good stead.

ERN: Is there a particular image (or images) related to science or technology that you find particularly compelling or instructive? Why do you like it; why do you find it compelling or instructive? Can we get a copy or pointer we can include with the interview?

MG: I find the image of the first silicon-on-glass module we produced on our “spin-off” company’s pilot line in 1998 particularly compelling. Whenever I see it, I think of the enormous effort from the talented team of people that got the technology to that stage, and also of the even larger effort involved in taking the technology from that stage into commercial production. Getting new technology into production can involve a huge effort but, I hope, worth it when the technology is as important as this.

ERN: What are your interests outside of work, and how do they inform how you understand and think about energy, and science and technology in general?

MG: I am fortunate in having a job which is also my hobby. I also enjoy travel which the worldwide interest in solar energy allows me to indulge, meeting new people, experiencing different cultures. I think this gives me an understanding of energy issues from a large range of different perspectives. Closer to home, near the Sydney beaches, I enjoy jogging along the coastline and the occasional swim in the surf, plus involvement in the local community through the local surf club.

ERN: What are some of these different perspectives?

MG: I think the different perspectives are those of private citizens having to pay more for energy, companies supplying traditional energies, environmentalists concerned about impacts of energy use, and of course as a scientist with the perceived ability to impact the available options.


Back to ERN July 28/August 4, 2008

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