Acclaimed photovoltaics engineer and winner of the IET’s AF Harvey Prize, Australian Professor Stuart Wenham visited London recently to introduce his ground-breaking research and discuss his vision of the future solar-powered world.
The solar industry is experiencing a massive boom. In the past five years, the cost of solar power production has fallen by 80 per cent and efficiency has been growing steadily, such that even the most persistent solar sceptic has been obliged to review their position and concede that solar energy has a reasonable future. Hand in hand with the technology development, market growth arrived. In the past ten years, global production of photovoltaics has been showing exponential growth-rates, making solar the fastest growing industry in the world.
As the world’s pre-eminent researchers, including Professor Wenham, believe, solar energy still has not reached its full potential yet. “I think that probably over the next ten years we will see the price come down by about a factor of three and that’s what’s needed to enable photovoltaics to compete with any form of electricity generation anywhere on the planet,” says Professor Wenham.
The 57-year old engineer, who is the director of the ARC Centre of Excellence in Advanced Silicon Photovoltaics and Photonics and Director of Academic Studies of the School of Photovoltaic and Renewable Energy Engineering at the University of New South Wales, Australia, has witnessed the development of the photovoltaics industry from the earliest days.
Having helped to set up the first solar-cell production line in Australia in 1980, Professor Wenham nurtured the technology, whose potential many doubted, through all its teething problems. The efforts paid off. Last year, his team has introduced a method which would enable cutting the cost of solar cell production by half, while driving efficiency up by 20 per cent compared with what is commercially available today.
As a tribute to his work and acknowledgment of his results, Wenham has been awarded the IET AF Harvey Engineering Research Prize, one of the most prestigious scientific awards in the field.
Taming hydrogen to fix silicon
“We are pioneers in using lasers in the design and fabrication of solar cells,” Professor Wenham says. “It’s something we have been working on for quite a few years and we have progressively come up with several generations of technology, each improving on the previous one.”
In the late 1980s, Professor Wenham and his team used lasers to cut grooves into the surface of the silicon material. This enabled them to bury solar cell middle contacts down below the silicon surface, reducing shading and increasing efficiency. They achieved their first world record in efficiency of silicon solar cells and have broken it several times since, still holding it after more than 20 years with new generations of even more efficient technology.
While the first generation of technology was being commercialised by BP Solar, selling products worth billions of dollars that are currently being used all over the world, Wenham’s team was already up to their second invention – using lasers to dope the silicon surface.
“It involves the use of lasers to melt the silicon surface in very specific localised areas," he explains. "We incorporate dopants into that molten silicon while it’s in the molten state, which enables us to achieve quite a higher performance compared with what other people have been able to achieve as well as being a very simple low-cost technique.”
The technology was picked up by Chinese company SunTec, who turned it into a multi-billion dollar production.
The latest breakthrough arrived last year. In this case, the Australian researchers focused on hydrogen and how to control it inside the silicon solar cell and use it to fix defects in the silicon material.
“Hydrogen is a very small atom, much smaller than silicon, which means that we are able to get it inside the silicon,” Professor Wenham explains. “People have known that you can do this for decades but so far no one was able to move that hydrogen around and make it bond to the defects of the silicon in the way that we have managed to do.”
The key again was the use of lasers, this time to control the charge state of hydrogen.
“Hydrogen atoms that are inside the silicon can take three different charge states, they can be either positively charged, negatively charged or they can be neutrally charged,” Wenham explains. “In the past, engineers haven’t been able to control the charge states but through the use of lasers, we have worked out how to strip electrons off the silicon atoms and provide those electrons to the hydrogen atoms to get under control the charge state of the hydrogen and therefore determine whether the hydrogen will be positive, negative or neutral.”
By doing so, the engineers learned how to move the hydrogen around the silicon solar cell and make it attach to various defects that would otherwise have a negative effect on the cell’s efficiency.
Laboratory tests conducted have proved very encouraging.
Cutting cost by half
The price of silicon itself makes up the biggest portion of the total cost of silicon solar cells. The purer the silicon used, the higher the efficiency of the final product. However, this also results in higher cost. To remain competitive, manufacturers have to compromise on the quality of the silicon, which in turn affects the efficiency. The discovery of the Australian team provided them with a cheap patch to fix faults in the less expensive silicon, while maintaining or even increasing its efficiency.
“That’s where our new technology is so important. The manufacturers can still use the cheap silicon but they can now use this technology to fix up all those defects with hydrogen,” Wenham explains. “Consequently, they can make much cheaper solar cells but actually achieve higher efficiencies than they could before because the material is now acting as if it was the very best quality.”
Taming hydrogen enabled the team to increase efficiency of silicon solar cells by 20 per cent, compared with what is commercially available today, while cutting the cost by half.
“Most of the solar cells that are being commercially made today have probably about 19 per cent efficiency and we expect the solar cells using our new technology to be about 23 per cent efficient, so that represents about a 20 per cent performance improvement,” says Wenham.
“We invited the world’s largest silicon solar cell manufacturers to provide us with samples of silicon wafers they are using in making solar cells and we applied our new technology to those silicon wafers to show how much we could improve their quality. The results were so impressive that the companies are now funding our work.”
Wenham hopes to see his latest invention covering roofs of houses and car parks in three years. However, the mission is not yet accomplished for him.
Competitive with large-scale fossil fuel power generation
In 2013 in Spain for the first time in history, solar power achieved what is known as grid parity. Grid parity means that an alternative energy source can generate electricity at the cost that is equal or lower than the price of power bought from the electricity grid.
Since then, grid parity – a turning point in viability of alternative energy sources – has been achieved in a further 19 countries. That implies that small-scale solar installations no longer require feeding tariffs or subsidies to pay off.
“Solar energy has been identified by many experts around the world as the most likely contender for generating the bulk of the world’s energy needs as we get to the later stages of this century and in subsequent centuries in the future,” says Wenham. “I think the industry has got into a very exciting phase.”
Wenham believes that local solar energy generation can bring a real revolution to the developing world where billions of people still live without electricity and all the benefits it brings.
“Close to two billion people don’t currently have access to electricity and in that case they don’t even have the electricity grid. For them, the types of systems that they would need would be just small photovoltaic systems with a small amount of battery storage to provide them with the electricity that they need to greatly improve their quality of life,” Wenham says.
Whereas small scale photovoltaic installations have already proven their viability and the only thing holding back many potential customers is the high up-front investment needed to acquire the system, in the case of large-scale installations, the situation is still somewhat unstable.
“Small-scale installations only compete with the retail price of electricity, not with the generation price,” explains Wenham. “That’s the main drawback of large-scale centralised solar power plants - they have to compete with other centralised power stations such as coal-fired power stations or gas-fired power stations and so the price they are competing with is a much lower price for electricity before all added charges.”
However, Wenham believes, the day will come in the not-so-distant future when solar will be able to comfortably beat fossil fuels even in the large-scale electricity generation field. But even this milestone won’t be the end of the amazing evolution of photovoltaics.
“Photovoltaic technology will continue to develop over the next fifty to hundred years,” predicts the engineer. “Eventually thin-film technology will become dominant. Until the thin-film is developed, photovoltaics wouldn’t have reached their ultimate potential. My vision of the future is a thin-film photovoltaic technology with about 40 to 50 per cent efficiency produced at about ten per cent of the cost of the current photovoltaic devices. Until then, scientists like myself will still believe there is a lot of work to do.”
Engineering Oscar to help push the boundaries
A testimony to Wenham's status as a renewable energy pioneer, the IET’s expert committee awarded him with the AF Harvey Engineering Research Prize in early 2014.
Dubbed the engineering Oscar, the award - which carries a £300,000 cash prize - will help fund Wenham’s future research. However, the humble winner says it was rather unexpected.
“I am from Australia so an award like that is something you only dream about, you don’t expect ever to be fortunate enough to win it,” Wenham says.
“The Prize is a very generous one, one of the most generous prizes anywhere in the world in that field, and so what I am dedicating that prize to is to fund the very work that actually won the prize. That’s the new technology that we are developing at the moment in conjunction with many of the world’s largest manufacturers - using hydrogen atoms to improve the quality of the silicon material and therefore to raise the efficiency of solar cells and bring down the price.”
Given the track record of Wenham and his team, the world can expect to hear more from them. With a burgeoning acknowledgement of the potential of photovoltaics, the future of solar may be really bright.