July 28, 2008
UNSW's Martin Green
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
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
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
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
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,
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
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,
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
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
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
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.
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July 28/August 4, 2008