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Everything Electric Podcast
The Untold Story Of Solar Power & Why It Took Decades To Take Off! | With Oxford PV
01:03:57
In this week’s episode of the Everything Electric Show, host Imogen Bhogal chats with Dr. Chris Case, CTO of Oxford PV, about the groundbreaking potential of perovskite tandem solar cells and the future of solar energy. They delve into the...
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- [00:00]
Imogen Bogle
Hello and welcome to another episode of the fully charged show podcast where today we're talking all things solar power. Now, as many of you may know, solar power is the cheapest form of energy. In fact, cost of solar PV has dropped some 90% since 2010, and in fact, costs have dropped about 30% over the past year or so. Now, my name is Imogen Bogle. I'm one of the presenters and producers here on the show. And very shortly I'm going to be joined by our fabulous guest who goes by the name of Chris Kennedy Case. Now, Chris Case is CTO at an organization called Oxford PV where they are busy smashing all sorts of records because they create the world's most efficient commercially available solar panels, all thanks to a material called Perovskite. We have featured them on the show before, so I'll be sure to link to that episode in the description and at the end of this episode as well. But Chris, as well as being CTO at Oxford pv, he, he happens to be one of the most knowledgeable experts when it comes to all things solar. So in this episode we are going to dive right in and go through the history, which is totally staggering, to find out how we've got to these super, super efficient, cheap forms of energy. So buckle up, let's get in. But first, a very, very quick advert break. Love the Everything Electric Show. Then join us live in Sydney in March, London in April, or in Vancouver, Farnborough and Melbourn, September, October and November 2025. Chris, thank you so much for giving up your afternoon to join us for this podcast. We had a couple of technical difficulties to get to this point, so we're hoping that it will be smooth sailing from here on in. Now, what I imagine is that we are going to start this conversation somewhere up here and then we'll slowly open the drop down menus and see which rabbit hole we end up going down. So confusing a couple of phrases there. And the reason that I want to do that is because when we interviewed you back in the summer, when we initially came and looked at Oxford pv, we had such an incredible conversation off camera that I felt that the listeners had to come and experience for themselves. So thank you so much for your second appearance on the Everything Electric Show. Okay, so I want to start at the top. Most simple, most obvious question. What actually is a photovoltaic cell and how do they actually work?
- [02:23]
Chris Kennedy Case
All right, well, first I have to at least acknowledge. Thank you and nice to meet with you again and thank you for inviting me back. You Guys are busy, though. I can't keep up with the content. You release.
- [02:37]
Imogen Bogle
Too much content. Somebody.
- [02:39]
Chris Kennedy Case
You use the phrase rabbit hole. And I remember speaking to one of our. Our staff, and he said, you mean rabbit warren. But anyway, rabbit hole certainly does fine. Well, let me get to the answer to your first question. So I might begin by saying that a photovoltaic or PV or solar cell, and I'm going to refer to all three of those things throughout the conversation. So they mean the same thing, really. It's the simplest electronic device, so you need to understand it's made of a semiconducting material. So that should trigger a reminder from early science classes in school that most materials have one of three properties relating to conductivity. There are other insulators, glass or ceramic, they don't conduct. Or metals like copper and silver, and they very good electrical conductors. Or they fall into this sort of intermediate category, semiconducting. Somewhere in between insulating and conducting, there are lots of naturally occurring elements that are semiconducting on their own, like selenium, silicon, tellurium, germanium. They're usually found in compounds, but there are lots of synthetic semiconductors and even materials that can be made semiconducting by adding small amounts of other elements. But in the case of a solar cell, the material has one job. Absorbing photons, typically from the sun, and converting them, or it could be indoor light, by the way, and converting them into electrons, or more simply, electricity. That's why I say they're very simple, even simpler than transistors that make up all the integrated circuits that are ubiquitous in the modern world. And also think of them like a rectifier or a diode in some cases. Again, a very basic and simple device. In fact, it belies the history of the modern silicon solar cell.
- [04:28]
Imogen Bogle
One thing that really strikes me is that this is going to really expose how limited my engineering and science knowledge is at this point. But when you hear semiconductor, as you say, materials fall into one of three categories. Insulators, conductors, or semiconductors. For me, it doesn't seem obvious that you'd use a semiconductor to be used as a means to generate electricity. What is it about a semiconductor that makes it particularly ripe to be in a solar filtetic?
- [04:56]
Chris Kennedy Case
Yeah, I mean, okay, it's fair enough, but it sort of gets to the heart of how that solar cell device works, and it gets to the heart of the concept of a rectification or diode. But when the photons are absorbed in that semiconductor material, they generate sort of these electrons and their counterparts known as holes. And you've got to get them separated by an electric field which is actually built into the device in the form of. Of this semiconducting material naturally has this electric field which separates the carriers. And then the trick becomes how to get those carriers out. You know, like connecting the positive and negative of a battery to the world to do some function. If the material was purely metallic, so a metal, you know, the photons would sort of be absorbed. But you know, what happens when you have metals typically, right, they're reflective, so the light would get reflected so you don't end up generating what you want to do, which is generating electrons that you could then convert or capture inside that device. And of course, in the case of the insulators, let's take an example, glass, you think of glass as often transparent. In that case, that's not doing you very much good. The photons would go right through the glass before they did anything useful in the way of making electricity.
- [06:16]
Imogen Bogle
I mean, it's really obvious when you say it, but I'd not stop to think that actually, of course, a metal would reflect that. It's absorption properties potentially not that brilliant for the use in solar pv.
- [06:27]
Chris Kennedy Case
I mean, it's got electrons in it, of course, that's what makes it, you know, have the ability to conduct very well. But those electrons, you may have remembered your phrase from, from school, a sea of electrons, and they're all throughout the metal. But again, that allows them to become very good as electrical conductors. And that's why the metals are used, you know, connecting distribution circuits to your home.
- [06:51]
Imogen Bogle
Now, it might surprise people that actually the solar panel as a concept in itself is pretty old now. And I wonder if you could describe the very first solar panel and sort of walk us through what, how it was constructed way back when and just how perhaps inefficient it was.
- [07:10]
Chris Kennedy Case
Yeah, I'm going to talk about solar panels that I think are most interesting in this discussion today, which are the solar panels that make electricity. But remember, there's another kind of solar panel which of course is used to produce heat or hot water. But you know, and that actually goes back, I think, to William Herschel in like the 1700s, who carry like a water heater on his trip through Africa. But anyway, unsurprisingly, the first solar panels for electricity were made from one of these naturally occurring semiconductors. In this case it was selenium. And in 1873 it was an English electrical engineer, Willoughby Smith. He was studying photoconductivity in this material, selenium. And it was pretty clear that those studies, you could convert, you know, what were images from cameras into light into electrical signals. But it was actually like 10 years later, I think, 1884, an American inventor, Charles Fritz, he was believed to have deployed what really is the first solar array on the rooftop of a building in New York City. And yes, indeed, 1884. I mean, that's a long time ago. I mean, he was hoping to demonstrate a way to generate electricity that did not require the complicated and large and bulky dynamos and generators that were just beginning to enable the electrification of the world and transform the machinery of the industrial age away from steam or water driven power. Fritz wanted to be able to power signaling systems. In fact, he wanted to power signaling systems across the first transatlantic undersea telegraph cables. It was quite a vision. But the conversion from sunlight to electricity was so low, around a half a percent, it was impractical. So in reality, he was not really the first person to demonstrate the conversion of light to electricity. But that's known as the photovoltaic effect. But he was the first person to demonstrate it as a solar panel with some practical use. Now, we could go back, if you want, and find out what the origin of the first detection of the photovoltaic effect was.
- [09:19]
Imogen Bogle
When was that? I'm guessing a little bit before 1884.
- [09:22]
Chris Kennedy Case
A little bit before. But it's fascinating because of the coincidence of years. It was 1830, 39, and it was a guy, Antoine Edmond Becquerel, and ready for this. He was 19, and he was experimenting in his father's laboratory, and he actually created the world's first photovoltaic cell. He was using silver chloride or silver bromide, and he was coating pieces of platinum and he immersed it in, I think, a saline solution. And when you sort of illuminate those pieces of metal, he got a voltage and a current. So that was the first sort of successful demonstration of what is known as the photovoltaic effect. But, you know, it's a couple of other things. There were four successive generations of the Becquerel family, all educated at a prestigious French school they called Polytechnique. They all became physics professors. But Alexander Edmond Becquerel, he was the son of Antoine, who was the discoverer of PI's electricity. He was also the father of Antoine Henri, who discovered radioactivity, and the grandfather, Jean Antoine, who was known for his work on relativity and the discovery of polarization in a magnetic field. So this was quite a family, but it was Edmund, who was intrigued by light and actually he went on to make other discoveries which eventually led to the use or discovery of something called phosphorescence and that ultimately was implemented in things like fluorescent waps. So pretty good.
- [10:54]
Imogen Bogle
What a family of overachievers.
- [10:56]
Chris Kennedy Case
A family of overachievers. Again, it's hard to comprehend that pedigree and also the age at which he did it, you know, 19. But just remember that year 1839, because I'm sure it's going to come up again in our conversation.
- [11:12]
Imogen Bogle
Okay, 1839, that is clocked in my mind. But jumping forward to 1884, I think safe to say the demonstration on the rooftop of in New York was not necessarily a rip roaring success. And I think what I mean by that is that it didn't sort of spark this. Oh my goodness, we should all be adopting solar panels and focusing all of our attention towards them. It took some time before they, you know, really came back into focus. Why was that, do you think?
- [11:39]
Chris Kennedy Case
Well, first of all, half a percent efficiency. And we could talk about efficiency, I think a bit later, but just wasn't enough to do anything useful, not enough power to do that. So you have to sort of figure out how did we get from that selenium material with its relatively poor conversion, relatively horribly poor conversion from sunlight into electricity to a modern solar cell which is today mostly made of silicon. And so we have to actually move over to the research Laboratory known as AT&T Bell Laboratories, which was in the United States. Now AT and T was the company that ran the telecommunication or phone system. So that's its history. And they were seeking a solid state replacement for the vacuum tube. And the vacuum tubes were the mainstay of virtually everything electrical and electronic from switching systems for telephony. Right. And also amplifiers. But you know, they get hot and they're relatively unreliable. So people are constantly, you know, replacing the tubes to keep the system operating. So their dream in the 30s was to replace this bulky and high powered and unreliable vacuum tube with something solid state. And by the way, you know, there's the same story with those first electronic computers like eniac, which were. And the computers that were used for the decoding in World War II of the enigmas, encrypted, you know, messages. They were using vacuum tubes and they were replacing them every hour to keep those machines operating. But anyway, so a guy named Russell Ohl, he was working Bell Labs, he was a metallurgist in the 30s. Also Jack Scarf and Henry Thur, they were melting this material silicon in tubes and cooling them and then measuring what was going to be their rectification behavior. And every time they melted an ingot, they would measure to see what the behavior was because they're again trying to make this rectifier, which is the same as a function, as a tube, right? It blocks current in one direction and conducts current in the other direction. It's the basis of the solar cell. And they couldn't figure out because sometimes it came out with one side of the ingot positive and the other side of the ingot negative. Now that's a funny story in itself because that's the origin of the P and N designations when you hear about PN junctions. So as ridiculous as it is, it was just one side became was more positive or negative than the other in the ingot. They didn't know how to control it though. But they cooled the ingots slowly and discovered that a slice they made sort of accidentally cut through part of the ingot, behaved as if there was a barrier right within the silicon. And remember I said these semiconductors act as if they have an ability to separate the carriers, the electrons and their counterparts, holes within the semiconductor device. So that little piece of silicon, this is like 1939, that they discovered these ingots was actually kept a secret at Bell Labs throughout World War II because Bell Labs had to focus on military development. Predominantly they were focused on radar, many other groups, and that material that they were working on was going to become the basis of the first transistor and ultimately first commercial silicon solar cell. So Russell from that group did notice that that piece of silicon converted sunlight into light, into electricity, and had 1%, this is 1939, and that was already twice as good as selenium. So they filed a patent, locked the stuff up in a safe and went away for five or six years. And then, you know, after the war, it was, I think, engineer Darrell Chapin, also at Bell Labs, he was charged to replace batteries in these telephone systems because in the like jungles where the humidity was degrading them and he knew about old's work. And they dug up the PN piece out of the safe and got permission to work on it. And after a few months they solved some problems. And they actually are credited with inventing the first practical silicon solar cell. In 1954, Bell Labs announced that sort of invention with Chapin Fuller and Gerald Pearson getting the credit. At that time, the cell was 6% efficient. And just two years later, they offered a solar panel. And they called it the solar battery. In 1956. But to me, I find that sort of the history of all the vagaries of things, you know, from selenium to germanium, because the first transistor was germanium, could have been silicon, but they used germanium. They first tried germanium for the solar cells, but because they came across this silicon slice, discovered it was much, much better. So you got the choice.
- [16:39]
Imogen Bogle
But I think this is the thing that I find so fascinating because, you know, if we rewind back to 1839, when the first photovoltaic effect was. Was first demonstrated or discovered, and then, you know, through the. The 1930s, thinking about, okay, well, we need to kind of find an alternative solution to these vacuum tubes. No way could they have possibly imagined that where we would be in 2020 for what this podcast will be going out on 2025, whereby solar cells have been deployed at the rate that they have, that they are, the efficiency that they are, and that they are so cheap. And I just think it sort of really hammers home that point of this is the value of academic exploration and experimentation and, you know, going through those measures of, well, could germanium work? We think so, maybe. Or perhaps silicon is good. And maybe that's a very naive perspective, but I think it gives me a lot of hope about the role of, yeah, academic exploration, I suppose.
- [17:35]
Chris Kennedy Case
Well, of course, the science is great. Although another oddity at the time, the explanation of how the conductivity worked in that first solar cell wasn't actually published for another, I think, six years. So 1954 they introduced. It wasn't until 1960 that, or maybe it was 1959, they published a paper on sort of the fusion of carriers inside these solar cell materials. Now, why I find that kind of curious is it tells you that you can't always wait until something is fully understood. If you want it to sort of, you know, get commercialized and adopted, you have to sort of introduce it when it's good enough. And it'll get. It'll get improved, of course, with time. And I think that's one of the things that our company, Oxford PV has done, I think reasonably well, is to try to get products out when they're good enough, because otherwise we'll wait forever to solve the world's problems. But PV really, in the 50s and 60s did not have much go in the market outside of a few special applications.
- [18:48]
Imogen Bogle
And so I suppose the obvious thing that happened sort of not long after that information was published in 1960 was, of course, the space race. And presumably that's when the first Sort of commercial application really came into fruition. Have I got that right?
- [19:05]
Chris Kennedy Case
You do. And in fact, and although again, I'm sort of weaving into some of this story, some of the oddities of coincidences that have happened, you know, both in the history of PV and sort of in my career too, where there's some funny coincidences about stuff. So in the early years, I think it was 1956, William Cherry from the US Signal Corps, he went to another famous laboratory like AT&T called RCA Labs, and he asked these two guys, Paul Rapoport and Joseph Lafersky, about developing photoltic cells for satellites. Now Professor Lefersky is also known as the father of the tandem solar cell. I mentioned this as one of those odd coincidences because Bill lefersky was my PhD thesis advisor. And of course it turns out the product that our company is commercializing is a tandem solar cell. But anyway, within a couple of years they were producing solar cells for satellites. Vanguard 1 was the first one, used a small solar cell that they made. I think it was just one watt. But within a few years they were producing panels and Bell Labs launched what's called Telstar. That's the first. It was the telecommunications satellite. So telephone communications were beamed anywhere in the world from this satellite with a 14 watt sort of EV array that had been constructed. So despite, you know, attempts to commercialize the solar cell for other applications in the 50s, 60s, it really, the success was mostly empowering satellites. And today it's the accepted energy source for space applications. But you know, other applications developed, including applications for, you know, residential panels. But they've taken a long time and predominantly it's one problem, energy remained from fossil fuels to inexpensive.
- [21:02]
Imogen Bogle
And I suppose that's the thing because so you did your Undergraduate and your PhD at Brown University in the States and then you went on to Bell Labs. And so throughout your academic career and then your career after that, you've been focused on PV cells. What was it that piqued your interest at that particular point in time? Because it certainly wasn't the opportunity for residential solar at that stage.
- [21:27]
Chris Kennedy Case
No, in fact, I'd have to say that without admitting the date where I did some of these things. And it was a long, long time ago, but it was actually in the same galaxy that we're in. But I was definitely influenced, I think as many were at the time, by a number of things. One was a book called Silent Spring by Rachel Carson. Two, just in general, the challenges of generating energy that did not pollute or reducing environmental footprint. Remember this is a time when there's a rising awareness of what was called global warming, even though we were aware since the 1800s of global warming. But there was a rising awareness. Reducing emissions. They were all hot topics in the 70s and 80s. I actually did an internship at the United States Environmental Protection Agency in one of its early years. See if the epa, by the way, survives the next presidential term. But anyway, and I built my first solar cell when I was on what's called a Fulbright scholarship overseas. I was doing that at a French university, so it was pretty logical to work on solar cells. And then that transitioned to building a solar house and things like that. But it was also, but sorry not to stop you, influenced, don't laugh, by that quote from Edison from, I don't know, 30 or 31 where he said, I put my money on sun and solar energy. What a source of power. I don't. I only hope we don't wait until oil and coal run out before I tackle it.
- [23:04]
Imogen Bogle
I've not heard that before.
- [23:06]
Chris Kennedy Case
Well, this is 1930, so people look at the guy Fritz. 1883, 1884, 1931, Edison. These are really visionary people. It's just unfortunately, sometimes it takes a long time and it isn't always because you're fighting technology and because you're fighting geopolitics. But anyway, we'll get to that.
- [23:31]
Imogen Bogle
So I think safe to say. So you built your own solar house. When was this in relation to the oil crisis? When the cost of energy finally really started to hammer home for people.
- [23:43]
Chris Kennedy Case
Right. So I consider the oil embargo in the 70s, and I think it sort of started and it lasted a number of years. I mean they called it the oil embargo, but it was really a number of years before the supply of oil was freed up predominantly from the Middle east about. So this was a number of years after that. But it was the oil embargo that sort of pushed many of the oil companies into exploring alternatives to fossil fuels. So companies like BP created BP Solar, ARCO created ARCO Solar, Exxon created Exxon Mobil, all with the stated intention to find an alternative. And I have to say as soon as that tap started flowing again in the early 80s, all those things shut down. So we won't necessarily make a comment about what their true interests were. But.
- [24:43]
Imogen Bogle
It'S clear some knowing and nods there. But it's so fascinating because, you know, there was such an opportunity to seek out those alternatives. And I imagine that from a funding, from an academic funding perspective, actually during the oil crisis it was probably quite a good time to be researching these things. And actually, I imagine there were a number of step changes with regards to the improvements.
- [25:07]
Chris Kennedy Case
Well, much of the sort of development that has led to modern silicon solar cells in terms of their advancements from an efficiency perspective came out of research that began in the 70s and 80s, much of it sponsored by places like what today is called nrel, the National Renewable Energy Laboratory, but as at the time was the Solar Energy Research Institute in Colorado and also places in Australia like csiro, all pushing to advance the development of solar cell, both silicon and alternatives to silicon. Because people did recognize, and I didn't make a comment earlier, that although silicon was the selection of that first solar cell in 1954, it's actually not a very good material for solar cells, despite it being 95% of solar cells sold. It's fundamentally, you know, if you asked a scientist, what would you pick? They would definitely not pick silicon.
- [26:03]
Imogen Bogle
But this is something that we absolutely need to come back to because I think it leads nicely into what you're doing in the world of Oxford pv. But before I do, I just wonder if you could describe the solar house that you built because, I mean, what an astonishing thing to have done. And especially because, you know, we're talking, I'm guessing here, but I think it was in the 70s, right?
- [26:24]
Chris Kennedy Case
Nope, it was in the 80s.
- [26:26]
Imogen Bogle
It was in the 80s. I mean, even then, still absolutely astonishing.
- [26:32]
Chris Kennedy Case
So this, yeah, but this was sort of a project that had, it had support, by the way, so we were able to raise funds, you know, to get things partially donated. So that was kind of fun. And you call up a company and say, hey, I have this idea and project I want to do. Could you send me. And then you ask for something and you know, they don't always know exactly what you're trying to do. But companies, especially large corporations at the time, these included places like Dow Chemical, Dow Corning, they were very generous and open with those kinds of things. The asks weren't very big, but the house itself was meant to be sort of a very highly efficient house. So, you know, it was well insulated, well, you know, simple to assemble, very small at the time, you know, compared to what it was. And it was meant to be powered by, you know, some sort of photovoltaic system. And also it had lots of what at the time were passive designs, passive things. So that had rocks to store heat from hot air. It had, I don't know, I think it was 600 gallons of water tanks, 20 tons of rocks, by the way, the store heat in the form of air. 600 gallons of water to store, you know, heat in the form of water. And, you know, you're just moving energy around depending on where you want to put it and where you have access to store things. I remember the challenge for the rocks was in that area, this was east coast, there was a lot of radon in the granite rocks. So we had to get rocks trucked in from the Middle west that didn't have radon. Otherwise you'd be circulating radon through your house, which, you know, not an ideal situation. And this. The solar cells which were produced by one of those companies, Arco Solar, were. Which, by the way, was the biggest producer of solar cells in the early 80s. They're the first company to produce a megawatt of solar cells at the time. And remember flying out to California to buy the solar cells from a friend of mine, Charlie Gay, who was at that company in California, and he was giving me a real break on the price and charging me $10 per watt. And they were 1 watt solar cells. Today's solar cells are 7 to 10 watts each. So they were 1 watt. And he said, I mean, you know, because they normally were selling for $40, even to sell them to me for 10, that was still a big, you know, big price. And today it was like 3,000 solar cells, 3,000 watts, 3 kilowatts, more than $30,000 worth of solar cells. And today you could buy solar cells that are twice as efficient for less than $1500, $30,000, less than $1500. That's the change. But that change has been driven predominantly not by technology, but by productivity and manufacturing enhancements, along with improvements in efficiency, many of which were sort of emerged in the early 80s, but just took a long time to get commercialized.
- [29:53]
Imogen Bogle
And so I think I remember when we were chatting previously, it was sort of the early 90s that residential solar began to take off again. And presumably that was because there was a greater focus on that productivity and scaling the manufacturing of solar cells in a big way. But. But also, I think there was a bit more funding available, and certainly from the government, I think, in Germany. Did that really help propel a more wider adoption of solar pv?
- [30:23]
Chris Kennedy Case
It did. And I would have to say that throughout the 90s, really, again, people avoided solar unless they were really interested in the technology, because fundamentally, it could not deliver energy that was less expensive than competing products. And most people do fundamentally have to make decisions based on cost. The payback period for a Solar array Investment in the 90s often was 20 years, right? People don't always stay in their homes for 20 years. Very difficult to do. But Germany introduced something, and Germany's motivation is they wanted to extract themselves off nuclear energy dependence. So they introduced this concept of feed in tariffs, where they actually agreed to subsidize people's installation on homes and also in businesses of PV panels and systems by buying back excess electricity at several times the market price. Now, effectively it's a subsidy, and effectively what it did is it changed the economics from being something that might take 20 years for return to in some cases, just a few years for a return on investment. But it also had the parallel sort of benefit of bootstrapping and prodding the German industry to build equipment that manufacture these solar cells. So in that time period, Germany was the leaders in the deployment of pv. And so there are many homes in Germany that were outfitted with PV panels at that time. In the 90s and 2000. Of course, at some point other things happened, but that did drive a big thing. The US adoption remained very small throughout all these time periods until relatively recently when the prices became sufficiently competitive that the energy actually is cheaper. And that, of course, is transformative when the energy becomes cheaper than any other form of energy.
- [32:34]
Imogen Bogle
So obviously adoption starting to rise in the 90s and 2000s, principally on the residential side of things. But that adoption is still sort of driven by the availability of subsidies or inadvertent subsidies, and also that constant sort of calibration of what is the cost of this array versus the cost of alternative forms of energy. And what does the payback period sort of look like for the average person?
- [32:58]
Chris Kennedy Case
And.
- [32:58]
Imogen Bogle
And then things sort of start to change as kind of the cost of energy becomes a little bit more volatile. The cost of solar panels continue to come down. They're now at sort of their cheapest point ever. And of course the efficiency increases at the same time. But when you look at that efficiency, if it was an exam score, I think safe to say generally you'd be pretty disappointed because it's around kind of the 20 to 23% for the average silicon score solar cell. And you mentioned earlier that silicon's actually potentially quite a bad choice, which I think will segue nicely into what it is that Oxford PV are doing. But I wonder if you could share with us why is silicon not so brilliant? And why is it that there seems to be that cap on the possible efficiency that can be achieved Now?
- [33:43]
Chris Kennedy Case
You weren't referring to my scores on my first Latin exam in high school, are you? No, perhaps.
- [33:51]
Imogen Bogle
Absolutely not.
- [33:55]
Chris Kennedy Case
But first of all, let's just talk about silicon for a moment. And then at some point we have to talk about this, you know, material that our company is working on, Crossgrid. So hopefully we'll get to that. The material that has to absorb the photons from the sun, you know, should have a couple of characteristics. It should be good at absorbing, okay? And that's called its absorption coefficient. Silicon isn't a very good absorber. So it takes quite a thick hunk of material, you know, several hundred microns in thickness to absorb most of those photons. The other thing, and this should be sort of obvious, the sun's, you know, appearance is actually made up of many, many different spectral colors, right? That's why when you see it split by a prism, you see all the different colors in the rainbow. And each of those colors, of course, represents a different kind of photon energy. And the photons that come from the blue part of the sun, the part, the spectrum where you get sunburn, for example, as opposed to the red part of the spectrum, which is what you mostly feel heat from. Most energetic photons come from the blue part. But each material has a characteristic spot of that solar spectrum where it absorbs best. And silicon, unfortunately sits in the red part of the solar spectrum region. So it's not so good at taking advantage of those high energy photons and it can't be changed. That's a characteristic of the material. So it is inexpensive, so that is good. It's not a very good solar absorber. So that's not so good. It's what's known as an indirect bandgap semiconductor, which means it wastes a little bit of the energy, converts as heat, just doing the conversion, you know. And finally, it's just not well matched to the solar spectrum. And it also needs to be very, very pure to work effectively. You put all these things together, not ideal. But you think about, although efficiency is an important factor, right? And costs are important factor. The solar cell itself, you know, people are saying, well, we'll just continue to reduce the cost of the solar cell, but that doesn't actually drive further reductions in the cost of energy because the solar cell itself is just part of a panel which is part of, you know, a module which is part of a system which is part of a mount which has, you know, connected inverters and batteries and things like that. And if you look, trace back the fraction that's the solar cell, it isn't that big a fraction. So if you continue to drive down the cost of the solar cell, you don't actually reduce the energy cost that you're generating. So the only fix is to raise efficiency. And therein lies a problem that all materials that you know do this, all semiconductor materials that are used to convert sunlight into electricity have a maximum conversion efficiency. It was just sort of identified and calculated back in 1960 by Shockley and Queisser, two people, the Shane Shockley, by the way, in 1947, who was one of the inventors, accredited inventors of the transistor, also from Bell Labs. So again, all these funny threads through history. But anyway, in 1960 he wrote a paper that said the most efficient a solar cell could be under one sun's worth of illumination. The sun as it reaches the surface of the earth is 29%. And maybe we can spend a moment, explain what conversion efficiency means. So that's the limit. And over the time from 1954 to today, silicon's efficiency has gone from 6% in 1954 to over 25%. That's a huge increase, but it's coming at its limit. You know, it reaches a flat part of the curve. And there are some record solar cells, 27% type things, but you probably could not commercialize some of those devices. So if you want to continue to reduce the cost of energy, you need a step change in efficiency. And surprisingly that same person back in 1960 said, well, you could make multi junction solar cells. Yes, multi junction solar cell. And the simplest concept is two solar cells working together, either just stacked on top of each other, you know, directly or indirectly, but working together. And where one solar cell's absorption characteristics are tailored to a part of the solar spectrum, that's higher efficiency, like the blue part, and another part is tied to a different part of the solar spectrum. But putting those two materials together raises the efficiency number from 2943, which is that step change. That is a step change. And you know, again it goes back to, it's the multi junction solar cell, 1960. That work was read by this guy, Professor Lefersky, he thought this was great, he wanted to work on tandem solar cells. I eventually worked on, or ended up working on tandem solar cells. But that concept is what Oxford PV has been working on basically since 2014. This multi junction solar cell using two different solar cells, one of which remains silicon, but the other one is material known as perovskite.
- [39:29]
Imogen Bogle
So just to check that I have understood correctly before we get into a bit more about what is perovskite and Some of its qualities that silicon pretty good at absorbing energy in the infrared spectrum from sunlight, but actually the higher energy is in the blue part of the spectrum, the sort of UV bits. So actually to improve the efficiency and the amount of sunlight that you're converting into electricity, you want a system that can maximize the amount coming from the red bit, infrared bit of the spectrum and the UV bit of the spectrum. And you can do that through tandem cells such that you've got one material optic red and another one trying to go for blue. And that's where perovskite can come in. Because through this tandem approach, you can get the best of both and sort of broaden the spectrum that it could absorb from.
- [40:17]
Chris Kennedy Case
Absolutely. A good characterization. Although I might add, if you picked another solar cell material than silicon, you could pick a material that was better by itself. An example of that material is gallium arsenide. Gallium arsenide has an absorption that is in between sort of the red and blue. So it's closer to the blue and it's a direct band gap semiconductor. So the efficiency theoretically is 33%. So today, gallium arsenal solar cells by themselves can be more than 30%. That's pretty good, except for a couple of problems. There is enough gallium in the world to make, you know, terawatt scales of pv. And the other material, arsenic, is probably not something you want to, you know, develop further and exploit in production because it's quite hazardous and toxic. And finally, the production is very expensive. So none of these things bode well, but it is a good material. And that's why most space solar cells are derived from materials like gallium arsenide. But there you can afford things that are a thousand times more expensive because they go up into space on very costly satellite launches.
- [41:35]
Imogen Bogle
And I suppose that's the challenge, isn't it, that it's not just looking at the efficiency of material as you describe. It's cost availability, manufacturer ability, manufacturability.
- [41:45]
Chris Kennedy Case
Right, Yep.
- [41:45]
Imogen Bogle
Manufacturers. There we go. Scalability, recyclability, probably, and durability as well. And probably a whole host of other qualities that I've missed as well, which is, I suppose, what makes perovskite a compelling option.
- [42:01]
Chris Kennedy Case
And it is. And so should we go back to the perovskite story?
- [42:07]
Imogen Bogle
Yes, I would love to, yes.
- [42:09]
Chris Kennedy Case
All right, so just, you know, to make it clear, Oxford pv, our company is commercializing a solar cell product based upon what is known as really technical, but a 2 terminal perovskite on silicon tandem solar cell. We've talked about tandem, so that is means just two. So only two solar cells are involved here. One is silicon and there's this material perovskite. You could have more layers. We've chosen two. And the two terminal just means we put our perovskite directly on the silicon. And our mission vision are simple to make this material the mainstream PV material. For all the reasons that I'll explain in terms of its characteristics while driving the world to electric future. So what is perovskite? It's just a mineral. It's a rock. Seriously. It's a rock with the chemical name calcium titanate. It was identified during a field trip to the Ural Mountains by Gustavus rose in 1839. Okay, no way, no way.
- [43:22]
Imogen Bogle
I had circled 1839 because I was like, I have to make sure that we come back to this.
- [43:26]
Chris Kennedy Case
Right.
- [43:27]
Imogen Bogle
I'm so glad that we have. So just so everyone is on the same page. 1839 was the same year that the photovoltaic effect was demonstration discovered. So same year also found calcium titanate, which is the basis of perovskite.
- [43:42]
Chris Kennedy Case
Right. For solar up case. I find this unbelievably curious. Not, you know, mystical or anything else, it's none of that kind of stuff, but just curious. And I, I think I pointed this out 10 years ago. Anyway, he proposed naming it Perovskite in honor of a Russian meteorologist and nobleman, Count Lev Alexei von Perovsky, who was also the Minister of Internal affairs under Nicholas I. He wasn't a scientist, but he was an avid collector of minerals and he actually began the Russian Geographical Society. So this funny thing. So all minerals are characterized by a crystal structure. Right. So are the perovskites, and that's the orientation and arrangement of the atoms that make up the crystal. And as any crystal compound. Right. The properties depend very much on what those elements are. So for perovskite, with a generic composition known as ABX3, you can substitute other atoms, leading to dramatically different electrical and optical properties. Some perovskite compositions are the basis for high temperature superconductors, which are used for the high performance foundation magnets in magnetic resonance imaging systems. So a mainstream application for decades. In fact, the first commercial use of perovskites is back in World War II to encapsulate nuclear waste. Wow, those are odd things. So these are not new materials, obviously discovered in 1839, first described in a publication back in the late 1800s. Anyway, we substitute for the calcium and the oxygen and titanium, other inorganic and organic materials, and they create this perovskite with the same crystal structure as the calcium titanate, this time performing as an excellent, really excellent solar cell absorber material. And I like to think of this as the same difference between salt and diamond.
- [45:40]
Imogen Bogle
Yes, right.
- [45:41]
Chris Kennedy Case
Both have the same cubic crystal structure, but you have to admit, pretty different characteristics. Not readily confused. Right, so, so these perovskid absorbers are distinguished from, you know, their silicon counterpart by being direct band gap. So they actually have the potential for 33% efficiency by themselves. There are these intrinsic semiconductors, so they don't waste energy in the conversion as heat. Very high absorption coefficients, in fact as high as gallium arsenide and something called very high defect tolerance, which means they're easy to manufacture, they tolerate impurities and defects very well, so they don't have to be made very crystalline like gallium arsenide. Silicon have to be and as you pointed out earlier, can be synthesized from inexpensive earth abundant materials that are found in lots of places, including multiple places that are outside of conflict regions. If you're worried about, you know, this concept of conflict minerals or the availability of rare earths or those kinds of things. So that's pretty good. And that's this material that we use in this multi junction solar cell.
- [47:02]
Imogen Bogle
So at the moment there is this new theoretical limit of 43% and so far you had a cell efficiency of 26.9%. So presumably your work will be done when you start sort of bumping up against the, the 43% mark.
- [47:21]
Chris Kennedy Case
Right. Well, first of all, you know, back at the beginning, I think in 2009, Japanese researcher Kojima San was working on this material and you know, they were a few percent efficient. These early solar cells were done. Today the record efficiency for this construction, which this tandem construction of Perovska and silicon is 34.6% held by a solar company in China called Langi. And it's an unbelievably unbelievable demonstration right now. That particular device is small, so it is not a production ready commercial product. But what it does do is convince you that we are on a path to that 43%. Not all the way, remember you can't quite get all the way, but probably into the high 30s. And that's a great demonstration. What's important right now is what we call a commercial size solar cell. And that's that solar cell that you refer to. And that actually is a cell that's large enough to be put into modules, and the modules are large enough to go, you know, out into the field or onto Homes, et cetera. And we've been now shipping modules with those solar cells. Actually, just this year's first time, we started to ship to our first customers. And yes, they are not 39%, they're not 34.6%, they're not even 30%, but they are definitely between 27% and above to be able to ship reliably those modules. But they already produce a module whose module efficiency, the completed modules efficiency is higher than anybody else's. So they're a step on the path to the future. And they're very much in demand from our customers who want to try them out in anticipation of the next generations. And we've been, you know, raising the efficiency something like 1% per year, seven or eight years. And I don't see why we won't continue on that path. Just as silicon continue to increase in efficiency over its history, perovskite will increase in efficiency. And already others have demonstrated, you know, in small area, those same kinds of benefits.
- [49:45]
Imogen Bogle
Do you know, it was so amazing coming to visit earlier in the summer when we did. And I think I joked at the time that we've had a number of shoots that have been in and around Oxford, and I myself live in Oxford. And each time we've had a shoot in Oxford, it's been a. Oh, no. I guess my travel time will be really straightforward. And I felt very smug about it. But I think more than that, I think seeing innovations like yourself and organizations like Oxford PV within the city that I live, it makes me feel very proud to be here and to be part of this ecosystem. It's just astonishing to see those kinds of efficiencies building on this, you know, history that spans from 1839 to today. Okay, I'm really conscious of time because I know that I could carry on talking to you for another hour, but I'm sure our listeners will start to start to get a little bit distracted. So a couple of questions that came up from when we put out the episode that we filmed with yourselves, and one of them was questions around the durability of Perovskine. And the second was, well, brilliant that these are in commercial production and that there's big sort of commercial customers. When will people be able to get Oxford PV panels on their homes? So those are my two questions that I'm hoping that you can illuminate.
- [50:57]
Chris Kennedy Case
All right, well, listen, all solar panels have to have three characteristics, of course. They have to be efficient, they have to be low cost, and they have to be manufacturable. So Those three characteristics. And in the early days of perovskites, there were definitely questions about sort of the durability of this material. But we've worked very hard to improve their durability and now they meet customer expectations, you know, who are buying these quantities to try out. So although there are still further improvements that will happen with durability, I'd say today they're sufficiently durable to meet our launch customers expectations. But again, they will continue to improve. But they are not at all like the products that people were working on 10 years ago, and they're a lot of people working on it now. In terms of the question on residential panels, we've shipped to utility customers, so there's big customers things in the field. We've also shipped to customers in special segments such as aerospace and space, but for the moment we're heavily constrained by capacity or German factory. So I think we have some commercial and residential demonstration customers in 2025, but significant volumes really won't be ready until at least the end of 26. Sorry, even my friends can't get them.
- [52:28]
Imogen Bogle
By the way, but it's not a million years away. And I think that's the exciting thing.
- [52:35]
Chris Kennedy Case
And it's not a million years. In fact, I would say that if you have an opportunity or the ability to install PV in your home, don't wait. The benefits begin from that first light and last for decades. And we need all the PV we can get.
- [52:50]
Imogen Bogle
Yeah, and I think this segues onto my sort of final questions, which are perhaps quite meaty to be asking at the end of this podcast. But, you know, it's so evident that from a scientific perspective, these panels are increasing in efficiency, becoming cheaper, becoming easier to manufacture, that they're becoming more easily understood across the world as to their value on a property or as part of a utility scale energy generation. But so often these things boil down to geopolitics and the appetite and impetus to deploy them more widely. We also have huge concerns around supply chains and where manufacturing capability is currently concentrated. And so I wonder, if you were in charge, what would you do to make the deployment of solar that much more straightforward, that much more strategic, and perhaps that much more future proof so that we don't have these huge bottlenecks or sources of vulnerability through virtue of this supply chain being reasonably concentrated.
- [53:52]
Chris Kennedy Case
You remember the decades when the world talked about outsourcing. Outsourcing was going to be the future of manufacturing. Diversify the supply chain and suddenly it's about security and reshoring and having domestic content and Embargoes and tariffs and all these things. You know, sadly, I hate all of that. I really do. I just wish it was not part of the reality of the modern world yet. In fact, as we sort of hinted on the way during this conversation, geopolitics play a huge role. You know, today we have China supplying something like 90, 85% or more of the world's EV modules, and they supply an extraordinarily good product at an extraordinarily low price. Yet they're being challenged over that thing because people say, well, they're underpricing them and that's killing our ability to do the competition. Or they're built with challenges or concerns about forced labor. So some or all or many of these things could be true, but not all will be true. But regardless, they have the. It's kind of, that's built up the capacity that has delivered, you know, the more than a terawatt of PV that we've installed and that has brought us partway to, you know, scale of deployment that we need for net zero. So I don't really have a solution. I mean, I have desires about how we should change things, but I don't have a solution to the geopolitics. But in reality, each region should really manufacture modules locally because the glass itself is 95% of the weight.
- [55:49]
Imogen Bogle
Yeah.
- [55:49]
Chris Kennedy Case
And you know, you're shipping glass to hold a little bit of solar cell or tandem solar cell long distances, and they're actually emitting a lot of CO2 footprint just from that shipping. So at the very least manufacture the modules within regions for redistribution. Maybe the solar cells can be manufactured somewhere else and shipped to the module makers, but that alone would improve, you know, the situation from a CO2 footprint standpoint. But if you want to rebuild local manufacturing, then you need to commit to rebuilding local manufacturing. And in the US that came in the form of the Inflation Reduction Act.
- [56:32]
Imogen Bogle
It's true. And I think, you know, something that's become very evident to me throughout this conversation. Conversation is that, you know, actually don't wait. Number one, I think that's a really important point of this, that actually get going with something. Number two, don't wait for the absolute perfect product to be produced. Actually the minimum viable product or, or something that's good enough is good enough. And I think three, that actually you need to think of this as not just the complete package, but all of these different innovations or all of these different bits that can be manufactured as components that you don't have to have it concentrated in one place. What is the expertise that exists in a local manufacturing hub? Could it be the glass? And is that good enough? So I think it's. Yeah, definitely. There's a lot to think about, but what's so exciting is that we're not stopping, that improvements are going to come and there's still ways to solve this huge challenge, hopefully. Is there anything else that you'd like to share before. Before we close out this podcast?
- [57:34]
Chris Kennedy Case
Well, is that an open invitation to summarize my wishes and things?
- [57:38]
Imogen Bogle
Oh, yes, please. That would be wonderful.
- [57:41]
Chris Kennedy Case
All right, well, I'll try to do it reasonably fast, but, you know, today There are like 770 million people who still live without access to electricity. And they're mostly where you expect in poor places, Africa and Asia. Right. And it's hard to imagine, you know, doing homework, you know, at night if you don't have any of light. Or even the 2 million people a year who die from indoor emissions from cook stoves and solar power is really the thing that can change that. Right. You know, coal, oil, and Natural gas received $1.3 trillion in subsidies last year, and something like 30 billion was spent on renewable R and D. And yet these 10% of the world's population still are unserved. And so we have to connect, like 100 million people a year to give access by 2030. And I think, you know, we're falling behind that target. And, you know, with this ubiquitous agreement that the climate crisis is real, that, you know, energy from PV is the lowest cost of energy in the world. You know, I don't see why we can't do that. We still have to reduce our CO2 footprint, and we have to do it to meet net 0 by reducing 36 gigatons of CO2 per annum to 0 to 0 in 28 years. And transport is already 20 gigatons a year. So this is a big challenge. And so that means by 2050, 60 to 80 terawatts of PV have to be cumulatively installed along with wind power, which is also a renewable form energy. That means we have to maintain aggressive growth for a decade, like 3 to 4 terawatts a year. And what happens if we don't do that, if we don't target net zero? Well, I say not zero is not an option. This is not a battle between east and the west and, you know, north and South. It's a battle for our planet and survival. Let's get those people that have energy poverty connected. Right. You know, utility companies don't like to connect people who make a dollar a day. But if you bring in pv, you can build up new grid structures from homes to villages to communities. You change the balance and the power away from the energy industry and those huge corporations, and that changes something. Political influence and changes the influence of those same corporations. My future is a future where energy is so inexpensive it can solve other problems too. Lighting everywhere for safety, access to clean water because you can do desalination because you have such low energy costs. So the next 10 years will be key. Make them count.
- [60:38]
Imogen Bogle
And I just think we have to remember, where did this start from? It came from a 0.5% efficiency and the possibility to totally change an energy system in which energy could be essentially free. And what that unlocks free. It's astonishing what could be possible if we're all focused on that net zero target.
- [61:00]
Chris Kennedy Case
I'm sure I'll be excoriated for suggesting energy should be free, because then where's the business in it? But there's still business from now.
- [61:07]
Imogen Bogle
Well, I think it'd be an interesting thought exercise and perhaps that's where we should go on a future podcast. But for now, I think that's a wonderful note to end on. And I can only thank you so much for giving up your time. And yeah, I can't wait to listen to this back because there are so many juicy nuggets of facts in there that, yeah, I can't wait to share down the pub we didn't even use.
- [61:28]
Chris Kennedy Case
One of my favorite phrases is how much PV space do you need to cover, you know, to provide enough energy to cover the world?
- [61:35]
Imogen Bogle
Oh, well, actually let's, let's end with that fact because that would be great to know.
- [61:39]
Chris Kennedy Case
Let's, let's just do some quick numbers.
- [61:42]
Imogen Bogle
Okay.
- [61:42]
Chris Kennedy Case
510 billion square meters. And by the way you should be able to do that is the surface area of the earth. Fun calculation, right? 29% of that is land. So it would only take like 500,000 cubic meters, right. To cover the planet with a 1 micron thick film of perovskite solar cell material. And if you ignore the water part and just use the land mass part, that's about billion half liters of volume. So the material that you need for perovskites is not much. That's a fraction of how much paint is produced every year. But now if you look in terms of the actual land use requirement and you reduce it to like an electrical energy need, those 470exajoules of energy that the sun beams onto the planet's surface every 88 minutes. You know, which from the 1,000 watts per square meter, that is an energy man of about 570 exajoules, or 17 terawatts. That means we need 150,000 terawatt hours or 500,000 square kilometers. That's a little less than the area of the state of Texas at 696,000 square mile kilometers. Not sure what the Texans would think of that concept, but anyway, it's not that big a number. It's less than 1/2 of percent of the Earth's surface.
- [63:05]
Imogen Bogle
Wow. I mean, the numbers speak for themselves, I think, is what we're really we're saying there. Well, thank you so much for leaving us with that, with that nugget. And yeah, I hope that we can continue this conversation in a future podcast. That is all that we have time for today. Thank you so much to you for listening. Thank you to Katie from our team, who'll be editing this one as ever. Before you go, if you could do us one huge, tiny little favor. I was going to say huge favor, but it's actually a tiny little favor. If you could give this episode a like a comment or subscribe or share it with a friend. It is always so incredibly appreciated. It ensures that we can keep on interviewing fabulous people like Chris and unearthing the important, interesting and innovative stuff in this clean energy transition. But that's it. If you have been. Thank you for watching and listening.