vol 9, issue 7

Interview with Professor Stuart Wenham, winner of the 2013 AF Harvey Prize for Engineering Research

14 July 2014
By Amy Spurling
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 Professor Stuart Wenham

‘I was fascinated by photovoltaic technology, it was magic - too good to be true...’

Professor Stuart Wenham and the team at the University of New South Wales

Professor Stuart Wenham and the team at the University of New South Wales

We talk to Professor Stuart Wenham the 2013 winner of the IET’s AF Harvey Prize in his alma mater and current place of work – the University of New South Wales.

Professor Stuart Wenham, the 2013 winner of the IET’s £300,000 AF Harvey Engineering Research prize and director of the ARC Photovoltaics Centre of Excellence, has neither a PA nor a secretary. I walk straight into his office at Sydney’s University of New South Wales (UNSW) and find him in a pin-striped suit.

In May, Prof Wenham accepted a cheque from the IET for £300,000 after winning the prestigious AF Harvey Prize for his pioneering work with lasers at UNSW. This has led to the development of several new silicon photovoltaic technologies, which have increased the efficiency of photovoltaic materials – a project primarily funded by the Australian Renewable Energy Agency. With silicon being the most expensive part of a solar cell, this is a significant discovery.

He is passionate about the difference that photovoltaics (PVs) can make to the world. But how does one develop a passion for solar energy? “Ah look,” he says in his Australian drawl, “it was a bit of a hobby before high school. I was fascinated by the technology, it was magic – too good to be true. There were no moving parts, no noise, no pollution, it lasts forever if protected and doesn’t need maintenance.”

He studied electrical engineering at UNSW where Professor Martin Green, one of the world’s leading PV researchers, had recently been appointed. “He was very much a mentor for me, ” Prof Wenham says.

Early days

In the days before solar technology degrees, Prof Green taught solar-cell courses to post-grads. Prof Wenham, then an undergrad, got permission to attend. Prof Green, director of the Australian Centre for Advanced Photovoltaics, has won “every leading prize that the photovoltaic industry offers”, including The Right Livelihood Award, known as the alternative Nobel, which – Prof Wenham reckons – will perhaps one day lead to the original.

Upon graduation, Prof Wenham says he had a choice of 13 jobs. He chose to help set up the first Australian solar-cell production line. Tideland Energy Pty Ltd specialises in marine navigational aids, so they were making solar panels for the world’s harshest environments. Yet, in his own words, it seemed like a hobby because of how he enjoyed it and he would get a “real job” later.

He was offered a position at UNSW in 1983 by Prof Green. Educational growth needed to keep up with the impact they were convinced they were going to make. “It was not a question of if but when. In the mid-1990s PV technology could compete with fossil fuels,” Prof Wenham says.

So they developed a proposal with the dean of engineering, Mark Wainwright. “We had to justify Australia’s role as leading the industry in the future,” and eventually they got the funding required from the Australian government (through the Australian Research Council) to instigate this new degree. The department began in 2000 with 43 students. Now it has 500. It was the world’s first undergraduate degree in photovoltaics and is still the only degree of its kind.

The department, which lists quite a few world firsts, attracts top researchers and staff and many of their former students hold senior positions in top international > < firms (ie in most of China’s top 10 companies) and are inventors on important patents. Against this background, Professor Graham Davies, the current dean of engineering, nominated Prof Wenham for the AF Harvey Prize. He “thinks it is the premier engineering prize in the world. Mind you, he is from the UK”, says Prof Wenham, who says he feels honoured and fortunate. I have heard it likened to the Oscars for engineers. “Look, I heard that,” he laughs in agreement.

The lightbulb moment

Prof Wenham and the team used lasers for selective emitter formation and hydrogen charge state control to greatly enhance hydrogen passivation techniques for improving wafer bulk and surface qualities.

Passivation ensures materials are less affected by external factors. Hydrogen atoms can correct deficiencies with lasers used to control the process. But haven’t we already tried to add phosphorus to silicon to achieve the same result?

“Hydrogen is a much smaller atom than silicon so that it can potentially move around freely inside silicon,” Prof Wenham says. “People have tried for decades to make this happen for silicon solar cells and so did we.”

After studying hydrogen, the team realised it wasn’t moving around very well because it was adopting a certain charge that was incompatible with good mobility. However, hydrogen can take on different charges – negative, positive and neutral. Through lasers they realised they could control this. “People have never tried to control the charge state of the hydrogen atoms before when making solar cells. Controlling the charge state of hydrogen can drastically improve the ability of it to move within the silicon and its reactivity to enable it to chemically bond to the defects in silicon to fix them up. This can enable drastic improvement in the silicon quality and the efficiency of the resulting solar cells.”

Prof Wenham says that his lightbulb moment came after he got some perspective: “It was actually during a review for one of my PhD students, Phil Hamer, who was working on hydrogen passivation. He was presenting some great material from research on the reasons it is difficult to get the hydrogen to where we want it and to passivate the defects in silicon. It is said that identifying and defining a problem is half the solution. I was able to see and understand the problem from Phil’s presentation and come up with how to solve it.”

Prof Wenham and Prof Green have been working on laser-based technology to manufacture high-efficiency solar cells since 1983. Their pioneering of lasers in PV manufacturing got them a slot in the Top 100 Australian Inventions of the 20th Century from the Australian Academy of Technological Sciences and Engineering, while their ‘Laser-Grooved’ or ‘Buried Contact’ solar cells were used by BP Solar to power Sydney’s Olympic Village in 2000.

They are currently working to improve the quality of poor grade silicon. This is the dominant cost in a solar panel, he says, although it has gone down by 80 per cent over the past five years. Their research has been a part of that, he says, as have economies of scale. Large-scale solar-cell manufacturers are excited about the technology, says Prof Wenham, and those who fund the research can get a license to use the technology.   

At the moment, standard silicon can achieve 18-19 per cent efficiency, he claims, while high-purity reaches 21-23 per cent. His team’s near-term goal is to achieve 21-23 per cent efficiency – this is where the prize money will be put to good use. However, they are heading towards 30-40 per cent over the next couple of decades.

Improving technology

I wonder if this includes using blue and green sunlight – ie harnessing more of the solar spectrum. “Tandem-cell structures are able to use more of the Sun’s rays,” he replies, “but currently all solar cells are single-junction devices.”

They are designed efficiently but they are only designed for one part of the spectrum. “The peak for infra-red is one micron wavelength but the efficiency is close to 50 per cent if you can control the light.”

The reason silicon solar cells are less efficient for other wavelengths of light is that “silicon takes a certain amount of energy to break the bonds (1.12 electron volts) between adjacent atoms”. This releases electrons, which, when they move, create electricity.

Blue light has a wavelength of 400nm, which is two and a half times more energy than is needed to break a bond so that the extra energy is wasted as heat. Currently, tandem-cell or cascade cell technology (where different materials, with various levels of energy needed to break bonds and release electrons, are stacked on top of each other) can convert different parts of the solar spectrum (particularly blue light) at the same efficiency as infra-red. However, stacking cells is currently so expensive it is only used in space. But it’s only a matter of time, thinks Prof Wenham. “We will discover better ways with better materials so that we can grow cells on top and not stack.”   

So what happened to thin-film solar cells, which can use different materials and were supposed to be more efficient? They’ve been expected to take over since 1980, he says. In fact, when he set up the first silicon production line, he was told that it was a waste of time and silicon would be obsolete in five years. In five years, it was going to take another five years, he says. And so it went on.

“Crystalline technology has developed faster” because thin-film can’t overcome its stability and durability issues, he says. It has a shelf life, whereas he’s still got some of those original crystalline marine modules from 1981. “Thirty years old and they’re working as well as the day they were made.”

And what happened to concentrating solar thermal? Not so long ago, CST was supposed to be cheaper and better across a large scale than PV technology. Prof Wenham says this was the case when solar-cell technology was expensive, but now the cost has come down by 80 per cent and will keep coming down. He calls PVs “the fastest growing industry in the world”. Solar power will one day be cheaper than fossil fuels, he predicts.

Predictions and reality

When is the revolution going to happen? Governments don’t seem to be rushing to build giant solar stations like in the Mojave Desert in California. “Big plants are not the way to go,” Prof Wenham says, “generate energy where you want to use it and then you don’t have to distribute it.”

Should I get solar panels on my house? “If there’s plenty of sunshine,” he replies, before considering “what are the neighbours doing with their trees?” Well, actually we live in a patch of rainforest. “But there is still a lot of light even on a cloudy day,” he says. “You could still generate 20 per cent of your needs.”

The building we are sitting in has a lot of solar panels, using the department’s Pluto technology. As you would expect Prof Wenham never pays for electricity, instead generating his own for 10 cents rather than the 57 cents per kilowatt peak hour that he would otherwise be paying, he says.

However, there are other areas that aren’t keeping up. Battery technology is lagging behind, he says. If it had kept up, he wouldn’t need a grid to store his excess generated energy. Even the grid won’t pay for his excess, he says, as it doesn’t have huge storage capacities so surges in demand – such as half-time during the World Cup Final – can still produce blackouts.

Shouldn’t Australia be generating more of its energy from solar power, given the country’s legendary weather conditions? Only 1.6 million Aussie homes have photovoltaic roof cells. Prof Wenham laughs. “You say ‘only’ and I say, ‘wow, isn’t this great?’. Ten years ago there were basically none!” During a heatwave, this produces 10 per cent of south Australia’s usage. He thinks this is already significant.

“In most countries you can go up to 20 per cent without causing huge issues for the grid because peak in demand coincides with the generation.” Germany is the leader in solar power generation, but the US and Chinese markets are growing. Australia needs fairer feed-in tariffs, he thinks, and less red tape to make installing more efficient. The technology is already there for Australia to meet its 2020 targets early.

Are solar-powered planes next, perhaps? Prof Wenham’s prediction is more down to earth – panels on houses and car roofs. He predicts that as fossil fuels keep climbing in price, by late in the century solar panel costs will have come drastically down. So pretty soon it looks like we’ll all be doing it. 

Read our reporter Tereza Pultarova’s interview with Professor Wenham online at bit.ly/eandt-prof-wenham
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