Welcome everybody. This is 100 Climate Conversations. Today is number 25 and this series presents 100 visionary Australians that are taking positive action to respond to the most critical issue of our time, which is, of course, climate change. We are recording live today in the Boiler Hall of the Powerhouse museum. Before it was home to the museum, it was the Ultimo Power Station. Built in 1899, it supplied coal powered electricity to Sydney’s tram system into the 1960s. In the context of this architectural artefact, we shift our focus towards the innovations of the net zero revolution.

I’d like to acknowledge that we’re meeting here on the lands of the Gadigal people of the Eora nation, never ceded. I’d like to acknowledge the Traditional Owners, of course, and their ancestors, and I recognise their continuous contribution to Country.

My name is Nate Byrne. This lovely man sitting next to me is Martin Green, who I have the absolute pleasure of speaking with today. And he’s a pioneer in solar technology, a true pioneer. Martin is a Scientia Professor at the University of New South Wales. He’s also the founder and inaugural director of the internationally renowned Australian Centre for Advanced Photovoltaics. His research group has developed technology that is featured in over 90 per cent of the world’s solar photovoltaic panels. We are so thrilled to have him join us today, so please join me in welcoming Martin Green.

Martin, I would like to start by understanding a little bit about where you came from and how you got into solar as your life’s work. So, what were you doing when it grabbed you and how did it grab you?

I first got interested in solar when I was at university. So, I won a travelling scholarship. I was educated in Brisbane, University of Queensland, but I won a travelling scholarship to see the world, it was $80. So, I drove down to Sydney and visited AWA electronics in Sydney, and I got shown a solar panel there in 1969. So, that was the first time I saw a solar panel.

But during my university study I got very interested in microelectronics because in that era they were starting to put more and more transistors onto a chip. I think there are up to about ten, when I got interested, instead of 10 billion or whatever they can do these days. So, that was the all-consuming passion for a while, and I was visiting microelectronics companies on this travelling scholarship. But as I grew older, I said, ‘Oh do I really want a career in this area, making better chips, or is there something I can be doing with a bit more social impact?’ And it was about the time of the oil embargoes of the 1970s and solar suddenly became to the fore. And I realised skills that I’d picked up in microelectronics could be applied to solar energy. So that’s how I got interested in the field.

Now we obviously have had photovoltaics in one form or another for quite a long time, and long before we were openly talking about carbon free energy, at all. When you came to it, how would you characterise where we were with solar and how it had developed so far?

Yeah, I guess the first discovery that you could convert light into electricity happened back in the 19th century, Edmond Becquerel in France did it in 1839. But it wasn’t until 1954 that the first efficient silicon cell was made. And you know, 95 per cent of the cells made today are made from silicon. The start of the modern interest in solar was with that and there was a lot of excitement. It was made at Bell Laboratories, one of the pioneering laboratories in the US in telecommunications, and a whole lot of different areas. And it actually made a front page on the New York Times in 1954. You know, ‘Vast power of Sun is tracked by cell using sand ingredients’ or something like that, some headline like that. So, it caught everyone’s imagination and Bell Labs released photos of families crowding around a solar panel, obviously going to do something useful with it. But the costs then were just exorbitant because the semiconductor industry was just in its infancy in that era.

But they managed on the second US satellite that went up and that was the fourth in history, Vanguard 1, some proponents of the solar managed to get the solar cells installed onto that satellite, and it was a tiny little thing about this big, the satellite. And they worked really well, in fact, embarrassingly well. They lasted for over six years up in the top space environment and it was this satellite was beaming out a radio signal. So, it was a bit of an embarrassment because it was clogging up the airwaves. But that meant that the cells established themselves as a viable power source for powering equipment in space. So, when they started getting interested in telecommunication satellites, and the first of these was Intelsat in 1962, the solar cell was the first choice for the power source for Intelsat.

So, there’s very serious development of the cells to put on to Intelsat and that was sort of the start of an era of where cells were the dominant source of power for satellites, you know for the, well, even up to the present. So, their main application when I got involved was in powering satellites and they were incredibly expensive, but it didn’t matter because the satellite cost a bundle anyhow and the cells were just a minor part of the total cost.

Let’s talk about how solar panels actually work though. So, we’ve got sunlight and sand so far, but I assume there are few more steps involved. What’s actually going on when you put a solar panel into sunlight?

Yeah. Yeah. The operation is really very simple, but the physics is quite complex. And it wasn’t until the 20th century that you would have been able to understand how they worked. So, the solar cells were made before then, but they really didn’t have a clue what was going on in them, they were just, wow, this is great. But Albert Einstein, one of the things he did, of the many, was he proposed that light instead of just being waves that all the scientists of the 19th century had proven that light was made of waves, he said that when light interacts with matters, it acts more as if it was made up of little particles and they’ve since been called photons. So, you can regard the light as beaming these photons down on you. And photons have different colours, there’s red ones and violet ones and all that kind of thing. So that was the important thing, the light comes in little packets known as photons.

So, these photons enter into the material known as a semiconductor, and silicon is the best known one which has very special properties. But what the light does when it enters the silicon, the photon gives up its energy, exciting an electron within the atomic structure of the silicon into a higher energy state and in that state the electron can move through the silicon. The job of people like myself who design solar cells is to get all those electrons moving off in the same direction. So, then if you connect an electrical load, like a heater or something between the top of the cell and the back of the cell, all these electrons going in the same direction flow through that load and you get the photons in the sunlight converted into electrons in the load, which is electrical energy. So, it converts the Sun’s energy into electrical energy.

Did you recognise the potential of solar right away? Did you have any sort of concepts about how much we would be using it in the future?

I guess back in the 70s when I got involved, it was all a bit of a pipe dream, but there was oil embargoes in ’73 in the US and President Nixon launched what was called Project Independence to try and get the US less dependent on oil. And so, a whole lot of alternative energy options were analysed and solar cells was put on the table as one of these options. So, all we had to do was take the cost out of the solar cells. And people back then were projecting if we can get the cost out, it’s going to be a really useful technology because there’s no pollution and it’s very simple to use and so on. So, I guess from the early 70s there was this thought that it could provide a large amount of power sometime in the future but enormous barrier in that the costs were just thousands of times too high to be able to do that.

It was expensive and of course the efficiency was pretty shot as well. But it’s interesting that it was an oil embargo that was a major driver there, whereas now we’re looking at rather than necessarily a lack of oil, a lack of desire to use oil, because, of course, the situation with the climate. How do you feel about where we’re at right now when it comes to climate change?

You know, we’ve been slow off the mark in trying to address it, but fortunately, the cost of the cells has come down very rapidly over the last decade, and the timing has been just about perfect in that now there’s real pressure for action to mitigate climate change being developed. The cells are now cheap enough to use to do that. Back around the turn of the century, people were doing studies of how much it would cost to create a carbon free society. And in fact, American economist William Nordhaus got the Nobel Prize for his studies of how much it was going to cost. But with the solar cells now being so cheap, you’re going to save money by converting to them. You know, it’s a completely different scenario from what people imagined only 20 years ago in that now solar and wind have become so cheap that you can change to them without any economic disbenefit but actually a gain.

Where are we actually sitting at the moment with solar? How does it fit into the energy mix, perhaps here in Australia and more broadly across the globe?

Yeah well, last financial year 13 to 14 per cent of electricity in Australia was generated from solar and a similar amount from wind, slightly less, and then slightly less again from hydro. So, about a third of our electricity was generated from renewables, whereas ten years earlier it would have been mostly just the hydro that was the renewable supplier of electricity. But that number is going up very rapidly year by year. So, I think it’s doubling every three years. So, you know, like in three years’ time we’ll be up 26 per cent and if that trend continues will be up to 50 per cent by 2030 and I fully expect we will be, so 50 per cent of our electricity as soon as 2030 could be supplied by solar. And it will be mainly economics that are driving it, sort of with favourable legislation because of the climate change issue, so that’s all that needed. The economic benefit is there, you just need a favourable environment for the uptake of the solar and we’re going to see big changes over this decade and the coming one.

Can you tell me what does efficiency really mean? It’s something you’ve made huge improvements on, year on year. In fact, you’ve held records for the efficiency of the cells that you’ve created. Talk us through the problem of efficiency and how you’ve surmounted it.

Yeah. So, efficiency is a very important parameter of the cell and it’s one that we’ve been concentrating on for decades now. But the efficiency is just the ratio of the electrical energy you get out of the cell to the total energy in the sunlight falling on to it. But when we started, back in the 70s, the record silicon cell had 16 to 17 per cent efficiency. So, about a sixth, one sixth of the energy in sunlight was getting converted to electricity. And that’s not very high but because the source of the energy is free and abundant and not used anyhow, it’s really doesn’t matter from that perspective what the efficiency is, but it does determine the amount of cell area you need. So, it determines how much glass you need in the panel that the cells package into and the amount of aluminium in the frame and a whole lot of other things like that, mounting structures, even the transport of the cell to the site, are all determined by the efficiency because it determines the area of the cell that you need.

So, our initial work, we concentrated on trying to improve the efficiency of the cell. So, back in the early days, 20 per cent was regarded as a four-minute mile of the photovoltaic area, that’s what you might reach one day if everything went well. So, that became the focus of our work, trying to make the first 20 per cent efficient cell. So, in 1983, we got our first world record, and these world records are sort of certified in that to be able to claim one, you really have to have the cell independently measured by a lab that’s regarded as an authority in how to measure them. So, we had this 18 per cent efficiency certified, so it was the world’s first 18 per cent efficient silicon cell. And that started us on a 30-year period where we held the record for all but about six months within that time frame. Well, 31 years, actually. So, 30 years we held the record.

That has been one of the key factors, not the main one really, but one of the key ones in reducing the cost because you reduce all the amount of chemicals you need in processing and all that kind of stuff as well as you improve the efficiency. So, we aimed, once we got our first 18 per cent, we aimed for to get the first 20 per cent. It’s a bit like the Olympics, it’s like getting a world record was like getting a gold medal and you got plenty of motivation to push for the next one, a real buzz when you knew you’d got a new record. So, we got to 20 per cent in a few steps in 1985 and that attracted international attention and I think the Powerhouse might have even done a display of our 20 per cent efficient cell back then. But that was, it really established us internationally as the leading group internationally in this field.

But I’d done a paper a couple of years earlier that showed that you should be able to get to 25 per cent. So, 30 per cent was the ultimate limit, but you should be on to get to 25 per cent. So, we pushed on and we eventually did get to the 25 per cent efficiency and the cell that did that is what’s called the PERC cell, P E R C. It stands for a very technical term, Passivated Emitter and Rear Cell. And emitter just means the top, so it just means we fixed up the top and the bottom of the cell. So, that was what we were focusing on because the bulk regions of the cell, there wasn’t too much further needed doing there, but the surfaces of the cell were where a lot of the loss in efficiency was occurring. So, we fixed up the top initially and then that got us the 18 per cent and then after we got to the 20 per cent, we fixed up the back. So, fixing up the top and the back, we eventually got us to 25 and the PERC was a vehicle for doing that. And last year 91 per cent of the cells made worldwide were PERC and the whole world acknowledges that it’s Australian developed and invented technology.

How efficient are you going to get things? Is there a hard limit?

Yeah. For a silicon cell there’s a hard limit around 30 per cent.

So, is there something that could smash through that 30 per cent? Is there a material, something other than silicon?

So, that’s what we’re working on now. We’re trying to improve the efficiency substantially. So, silicon has a photon threshold that’s in the near-infrared. So, it can convert all the red photons and even photons with lower energy in the infrared. But some other material, similar to silicon, can only convert blue photons, for example, and they can convert the blue photons more efficiently than the silicon, because they don’t waste as much of the blue photon’s energy as a silicon cell does. So, if you can stack a cell that’s good at converting blue photons on top of a silicon cell, the sunlight can fall on the stack and the cell that’s good at the blue photons grabs all the blue photons and converts them. But because the other photons don’t have enough energy to create any excitations in that material, they just pass through to the cell underneath and if it’s a silicon cell, it loves the red photons so it converts them efficiently.

So, by parcelling out the photons in that way, you can get a higher efficiency than just from a single silicon cell. So, adding one cell to silicon, you get like a 40 per cent relative boost but you can go further and add a virtually infinite number of cells on top of the silicon, giving them a smaller and smaller range of photon energies to convert and you can go up to 68 per cent efficiency in principle, compared to 30 per cent for a silicon cell. So that’s what we’re working on, trying to find a material that you can stack on to silicon that can convert some of the higher energy photons that the silicon doesn’t handle too well.

But the problem is, silicon has four attributes that make it really good for solar: it’s abundant, so that means it’s cheap and readily available; it’s nontoxic, which is great if you’re going to be installing them over one per cent of the world’s land area, you only have to cover 1 per cent of the Earth’s land surface area to generate all our primary energy from solar. So, it doesn’t sound like much, but if you work out how many square kilometres that is, it’s quite a large area involved; it’s got to be stable, so some manufacturers now warrant the solar panels for 40 years, so everyone warrants for at least 25, but some are doing up to 40 now; and it’s got to be able to give high efficiency is the other feature and that’s – so those four attributes. We haven’t found a material that ticks all those four boxes in the same way that silicon does but we’re working hard on it, that’s our big challenge. We think the efficiency of the panels can double in the fullness of time. So, by 2050, the solar panels are now about 20 per cent efficient, the ones you can buy commercially will be more like 40 per cent efficient, further down the track.

This work has been done through the University of New South Wales, Centre for Advanced Photovoltaics, 120 PhD students, I think, so far is that, is that right? What’s some of the work that they’ve done because they’re there all around the world.

Yeah. So, I personally have supervised 120 PhD students in my career, many of them have gone on to do great things. But one in particular was Dr Zhengrong Shi, who I think many people might have heard of, but he’s famous because he became the first solar billionaire. So, he was my 12th PhD student of 120, he was a really good student and we had him employed in one of our spinoff companies, but he was getting anxious to actually do something real, rather than research. He wanted to set up a manufacturing plant to make some type of solar cell. So, he was born in China, although Australian citizen by this stage, but he became interested in setting up solar cell manufacturing in China where there was no commercial manufacturing occurring there then. And we’d been over a few years earlier to look for the possibility of joint ventures to get some of our technology into production there and it just looked hopeless. So, we said, ‘Oh, Zhengrong, you know how hopeless that’s going to be.’ I was very pessimistic about his chances of success.

Anyhow, we gave him all the help we could and he set up the first manufacturing line in China in 2002. But he made a huge success of it because Germany had just started a feed-in tariff program that sort of subsidised the cost of installing solar. Even though the cells were much more expensive then than now, you could go to the bank and get a loan to buy the cells because you’d get paid the amount for the electricity they generated that would cover the costs of loan repayment. So, it was a feed-in tariff scheme that gave you an exaggerated price for the panels to make it economically viable and that really built up the market. And Zhengrong could make the cells a lot more cheaply in China than the German manufacturers could, so he was doing well, selling the cells into the market and using the profits to expand his production.

So, his success in doing this was noted by some US investment banks like Goldman Sachs and Morgan Stanley, some of the big names in the venture capital business and they encouraged him. He was backed, like he had to pedal his wares around China, so it wasn’t sort of cobbled up instantly when he said he wanted to start making cells. But Wuhan government twisted the arms of a few local companies that were profitable and they put in a million each, so he started with $6 million and these venture capital companies encouraged him to do a management buyout of the original Chinese investors and replace them by investors like Goldman Sachs that were well known internationally. And the original investors were really happy because they thought they had done their dough on this no hope venture. But it turned out that they got paid 18 times what they had put in, so they were very happy and they groomed Zhengrong’s company for listing on the New York Stock Exchange in 2005.

So, it was the first privately owned Chinese company to list on the New York Stock Exchange and it also turned out to be a huge success. It was the biggest technology float of 2005 with Zhengrong just listing a small part of his company’s shares, but it raised 400 million for a small part of his company, so he instantly became a solar billionaire because he owned a large part of the company by this stage. So that was really good for Zhengrong, he had this 400 million where a few years earlier, he had 6 million, so plenty of opportunity to expand much more quickly and everything. And between 2005 and 2010, there were ten Chinese companies manufacturing cells or interested in manufacturing cells that got listed on the US exchanges and six of those ten are in the top ten of manufacturers these days.

Zhengrong is probably my best-known student because of that huge success that he made and the way he triggered that sort of industrial transformation. So, all these cashed up companies started competing on a market that was a little bit artificial because it was this German feed-in tariffs scheme that was encouraging it, and the only way for them to sell what they were making was to be able to drop their costs. So, there was a massive drop in cost with the, you know, soon afterwards with all these cashed up companies competing for what was a limited market. And the six that are still in there today were able to do that and still remain profitable, so they’re the ones that were successful in keeping up with the drop in costs as the market forced them to reduce the costs.

It’s incredible to me that not only are you and your team making these solar cells just better and better and better all the time, but then also the same people are all helping to make them cheaper and cheaper, cheaper and more widely used. I wonder for you, what achievements are you most proud of? Let’s go, in your work and also just personally?

I don’t think we could be relying on solar to mitigate climate change in the same way that we are now, like the International Energy Agency’s latest strategy for getting us to net zero by 2050, calls for the immediate and rapid uptake of solar and wind. And the Intergovernmental Panel on Climate Change, their most recent publication on climate change mitigation says the same thing, the taking up solar and wind is the cheapest way of reducing carbon emissions quickly. So, I don’t think that all would have happened without Zhengrong’s initiative in setting up in China. And we played a big part in it, in helping him get the finance and all that kind of stuff that he needed and helping him technically set up a production line, that was set up by some of my technical people, helping him get production up and going and so on.

So, we played a big part in triggering the transformation that resulted in the cells being the present low cost. So, I’m probably proud of that. And then the PERC started getting taken up from about 2017, [in] 2018, it became the major cell in production, but the uptake of that technology reduced the cost of the cells by about a factor of two, we calculate, so we had an additional sort of impact later in the days through the PERC. So, we’ve really done a lot to get the solar cells to the cost that they’re at now. So, I’m very proud of that obviously.

In Australia, whilst we were kind of developing this love for solar, there have also been loud naysayers. I think probably, far fewer than the volume of their naysaying might suggest. But you know, the old ‘oh, when the sun’s not shining’ arguments. Where are we now when it comes to that? Is there any point in hearing those arguments anymore?

I think they’re becoming more muted. But we do need to change the way that we do things because solar, obviously you can’t rely on at nighttime. But the electricity supply network has had to rely on electricity not being available when it’s needed for a long time because a big coal plant can suddenly drop offline, for example. So, it’s had to have what are calling spending reserves just to counter that sort of emergency. But those spending reserves are very good for countering when the sun goes behind a cloud or the wind stops blowing for a while or something like that. So, the spending reserves within the grid network have been adequate when you’ve got small amounts of solar installed but obviously as you get more and more, you’re going to have to do something different to provide for the storage.

But interestingly, for nuclear, you’ve got sort of the opposite problem because with nuclear you essentially have to run the plants flat out, you can, like France is famous for having plants that you can turn up and down, but they don’t do it. If you look at the nuclear output in France, they just operate on constant output because as you vary the output, you go through thermal gradients within the whole reactor system and so on, which increases the need for maintenance. So, it’s costly to adjust the power output of a nuclear plant.

In some countries like Japan, you’ve either got to go off or flat out, there’s no option of running it. So, in Japan, for example, they installed a lot of what’s called pumped hydro, pump water uphill when you got too much electricity getting supplied and then let it run downhill when you need a bit more and turn a turbine. But Japan did that because of their large reliance on nuclear and not being connected to any other country, they had to balance things themselves. So, that’s been one storage mechanism that’s been available since the seventies when the nuclear uptake started occurring. But that’s ideal for solar as well and we have the Snowy 2.0 Hydro system going in which relies on that principle. So, you can use it for solar as well, except sort of upside down, you pump water uphill in midday and let it run it down at nighttime.

So, that’s one mechanism that is already available and then with the recent development of electrical batteries, particularly for electric vehicles and Elon Musk’s famous big battery in South Australia, that’s been a huge success. It does a lot of things within the electricity network much better than could be done before. So, not only does it provide storage, but it does a lot of things, balancing things that you need to do in the grid network that are much better than how it was done before. So, we’re going to see a lot more batteries also added to the grid to provide storage.

The other thing, Australia is very fortunate with renewables in we’re such a big country, so geographical diversity is really important because if it’s sunny in Queensland it might be cloudy in New South Wales or vice versa. So, the geographical diversity means if you have a good transmission system – and the transmission system runs all the way from North Queensland around to South Australia now – but if you reinforce that so you can send heaps of power from one direction to the other, you can use that geographical diversity, between sunny and non-sunny regions, but also between windy and non-windy regions. So, South Australia and Tasmania, they’re the best areas for wind and up in North Queensland is also very good. But if you, not only do you have geographical diversity within each technology but wind and solar complement each other very well in that the wind blows mainly in winter and mainly at night, so it’s like a good match to the solar. So, that reduces the amount of storage you need by having the grid strongly interconnected so you can shuffle power around from one region to the other. So, that’s the other thing that’s needed.

So, you have pumped hydro, battery storage, this transmission ability, and then the other big hope is hydrogen. So, that will provide a storage medium that you can store electricity indefinitely in hydrogen if you want to store huge amounts for long periods. So, I think things are pretty well covered, so there’s no real technical obstacle to supplying 100 per cent of our energy from renewables.

What does the future look like to you in terms of climate, where solar sits?

Yeah. So, I think we’re starting to see a bit of a push for solar uptake globally, worldwide and I think that’s going to accelerate and probably mainly because of the economics, I think many of the incumbent companies within the energy generation industry now accept that the future of coal generation, for example, is not looking all that promising. So, they’ve got to find a way of transitioning their company to a future that relies less on fossil fuels. So, I think there’s going to be accelerating interest in the uptake of solar and over the last year or so we’ve been very much supply limited in the solar.

So, the uptake has really accelerated, it could be the International Energy Agency, which in the past wasn’t all that favorable to renewables, but suddenly has changed its tune and they’re now saying we’ve got to install them as quickly as we can. I think that could be one factor because that’s a very influential body who many governments rely on for advice and in the past, they were saying, ‘Yeah, renewables can do a little bit in the future, but not all that much.’ But nowadays they’re saying, ‘Yeah, it’s got to – we’ve got to go quickly if we really want to address climate change. It’s really the best option we have is to install renewables as quickly as we can.’

And then the Intergovernmental Panel on Climate Change coming out with similar advice whereas they used to analyse all these future scenarios and it was always fairly limited use of renewables in their scenario. So, it took a while, it’s taken a while for everyone to catch up with this reality of these really rapidly reducing costs. So, over a 12-year period, the cost came down by a factor of 24, so it sounds quite remarkable, but between 2008 and 2020, that 12-year period, the wholesale price of the solar panels came down by a factor of 24 and that’s all just documented in the literature that keeps track of these prices. So, it just took the community as a whole, I think, a while to catch up with that transition that occurred because back then the solar was expensive and people were thinking, it’s too expensive to use. But then all of a sudden, that’s nearly overnight in geological terms at least, you’ve got these cheap solar cells.

I think by 2050, most of our primary energy will come from solar with wind playing a subsidiary role because of their complementary nature that I mentioned before.

Thank you so much for joining me and having this chat, this wonderful conversation. Please join me in thanking Martin.

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This is a significant new project for the museum and the records of these conversations will form a new climate change archive preserved for future generations in the Powerhouse collection of over 500,000 objects that tell the stories of our time. It is particularly important to First Nations peoples to preserve conversations like this, building on the oral histories and traditions of passing down our knowledges, sciences and innovations which we know allowed our Countries to thrive for tens of thousands of years.