This blog post is about the future. It's also a tale from the past. The content is based on a talk by Dr. Christopher Case, CTO of Oxford Photovoltaics (Oxford PV). A lot has happened since the summer of 2012. That was when I did a little project work in the group of Prof. Henry Snaith. Their research had led to the spinout company that is Oxford PV. Back then, we were all giddy with excitement over solution-processed perovskite solar cells. Our own plucky hero Mike Lee had voyaged to Japan and learned the ways of solution processing - leading to the production of 11% efficient solar cells. Considering the record for that particular material had stood at 4% efficiency only a few years earlier, this was incredible! Silicon solar cells had taken decades to make (and surpass) the same milestone. And here we had a wonder material with ingredients cheap as chips, that could be processed at temperatures much lower than what's needed for silicon PV. I did chuckle a bit at Chris Case's description of perovskites' self-assembly properties: you just spin-coat the solution and it forms a crystal layer all by itself!!! Which... thinking about it, is actually true. You can make a working solar cell (or a batch with at least one or two that work) even if you're sloppy. But good cells, consistently - like anything, that takes care. My job as vacation student back then was to try out vapour deposition (see picture below) as an alternative technique to try and achieve better, more consistent coverage. That is, instead of dripping solution on to a spinning glass plate, I put the powders the solution is made from into an evaporator chamber, where the powders are heated under vacuum and evaporate on to the glass suspended above them. (I'm glossing over a lot of preparation steps to make the glass electrically conductive, and heating the whole thing afterwards, depositing a hole-conducting layer over it, and silver electrical contacts on top of that.) Most of my cells were short-circuits, and my best one was 1% efficient. But Henry Snaith was sufficiently impressed by the mere fact that it worked, that he gave it as a project to one of his PhD students: And check this out: My 15 minutes of fame! Fast-forward seven years. Vapour deposition has fallen by the wayside somewhat, but spray-coating and inkjet printing are gaining traction. The composition of the perovskite material that caused so much hype initially (methylammonium lead iodide) was abandoned because it degrades too quickly - sometimes faster than you could stick it in an instrument to measure its performance! Luckily it's been superceded by new compositions, which when sealed in glass, have been tested as stable for 1000's of hours in challenging temperature/humidity conditions. Oxford PV's original aim was to make building-integrated solar panels (imagine skyscrapers with photovoltaic windows). I remember thinking it would be at least a decade before Oxford PV got any of their product on a building. And from what I've seen since of other start-ups, it does seem to take as long to get a new technology into full production as to raise a child. Turns out buildings are a very tough market to break into as well, though not unheard of - see Saule Technologies. Any small companies that dared to challenge the big established silicon PV manufacturers on making plain solar panels alone were quickly out-competed. The result? Technology stagnation. Trade shows packed out with identical solar panels. (And batteries too - trust me, I've been there.) Silicon solar panels will never be more than 29% efficient, no matter what you do - that is the theoretical limit, and in practice they're often not much better than 20%. CdTe and other thin films have a slightly higher theoretical limit, but the same problem in the end. Varun Sivaram talks about these problems in his book on innovation in the solar industry, Taming the Sun. So in a master stroke, Oxford PV decided to pursue an avenue that would turn the solar industry upside-down but make the established PV manufacturers into customers rather than competitors: by developing tandem cells. A quick science lesson/ reminder:
So Oxford PV's big idea: make perovskite PV coatings to turn existing silicon solar panels into tandem cells. Or, to use the term Chris Case coined, SILICON ON STEROIDS (meant in a good way). I was amazed at how many boxes this ticked, and seemingly so effortlessly:
** (Not that there's a shortage of usable land, but never say no to freeing it up for housing, agriculture or re-wilding) *** (The panels are no longer the majority of the cost - so a slight increase in their cost is well worth it to get more from the surrounding equipment) **** (Better yet, perovskites are better absorbers than silicon so you need about 200x less by mass - couple that with less energy-intensive processing, and the cheapness of the raw ingredients, and it's win-win-win!) Tandem cells are not even a particularly new idea. The reason I'm so hyped up is everything gets better with increased efficiency. I am so tired of people who say efficiency doesn't matter because wind and sunlight are free. Free resources still come with a cost to harvest them, financially and environmentally, in terms of material extraction and processing to make solar panels and wind turbines. My other bugbear, confusingly enough, is people fixating on efficiency. It's just one metric. You can't compare efficiency between completely disparate things. A natural gas power plant may be over twice as efficient as a solar farm, but emits around 400 g/kWh of CO2. Considering all the energy a solar farm will generate over its lifetime, the CO2 cost of manufacturing it averages out around 80 g/kWh. And that takes into account the efficiency of each. Back to the genius of Oxford PV. Their business model now is to license the perovskite PV technology to existing solar manufacturers to incorporate into their silicon PV products, to make tandem cells. And if they're not convinced? Hand over a few solar panels and Oxford PV will work their magic on them, as a free sample. Oxford PV had recently bought a factory from Bosch very cheaply because, guess what, Bosch had tried to compete with the giants of the solar industry, and lost. This factory needed some adapting before it could make perovskite PV, as it had been built for a CIGS production line (another kind of thin-film solar technology), but overall was considerably cheaper than building a factory from scratch. Expect the production line to begin rolling some time this year! So, what next? All-perovskite tandem solar panels one day, hopefully. They take so much less energy and materials to make than silicon PV, it's a no-brainer. There's a few all-perovskite tandem cells already in Oxford PV's labs. The challenge is in persuading existing PV manufacturers to abandon silicon completely in favour of perovskite.
In fact, it's still enough of a challenge just to persuade them to add a perovskite layer to their silicon solar panels. That's the thing with technology stagnation - once an industry starts failing to innovate, all they can do to grab market share is to lower their prices. Profit margins then become so slim that few companies have enough to invest in a risky new technology. Because let's face it, the SILICON ON STEROIDS rolling off Oxford PV's (formerly Bosch's) production line this year aren't going to be perfect right away. What will be wrong with them? Who knows! All they can do is make some, put them in a field, and see what happens. This is not an easy activity to fund since returns are not guaranteed. Some government funding can be applied for in the early stages, but once it looks close enough to commercial viability, there's an understandable reluctance to meddle with the free market (not that it stops government meddling in some industries...). There was some healthy skepticism of Chris Case's claim that the world could one day run on 100% solar power. It's true that you only need a small percentage of the Earth's land area to supply all of today's electricity needs; that even a modest step change in PV technology could completely tip the scales, as soon as it becomes cheaper than fossil-fuelled electricity; that transport and heating are perfectly capable of being electrified and a step change in pricing might just do it. But if you dabble with energy models, you get a feel for what it takes to get energy to where it's needed when it's needed. The task isn't as easy as some make out, but also not impossible. Chris Case had to concede that just because the world could go 100% solar, that's not necessarily the best option. A good dose of wind and nuclear, and pumped hydroelectric storage for balancing, might do the trick. Then there's my ever-present worry that human greed might be boundless. The discussion turned to Africa, and the suitability or otherwise of solar power. There's no doubt there are remote places where laying a cable from the main electricity grid, over land or sea, would be more expensive than installing solar and batteries. An audience member who had done some work for governments in Africa told us about their comparative eagerness to build hydroelectric power plants. It's simply not true that they're faster to build than solar farms - but who ever heard of a big factory run on 100% solar power? And there again it comes back to risk-averseness. Until something really bold happens in developed countries, it looks like there will be some reluctance in developing countries to be the world's guinea pigs.
7 Comments
Todd Flach
17/10/2019 11:41:41 am
Very informative and enjoyable read. Thanks for sharing! I am convinced the PV technology innovation cycle still has lots of potential left. And that it will give next-gen PV an unbeatable position in electricity generation. And we WILL NEED IT. The two apps are powering reverse osmosis seawater desal and distributing the potable water, and direct air capture of CO2 for mitigating global heating. These two alone will require 20-30 TW of PV capacity
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Susan
24/10/2019 10:41:09 am
Thanks so much for your comment! That is a good point about direct air capture of CO2 - I had always been a little wary of the idea because of the energy requirements of pumping so much air through such systems, compared to CO2 capture at source - but if we move away from burning fossil fuels at all, then what's left is very land-intensive BECCS, and DAC... :-/ Good luck, anyway - we need everyone in this fight.
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13/4/2022 03:53:02 pm
Solar Panel creates clean, renewable power from the sun and benefits the environment.
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13/4/2022 03:53:32 pm
What a Excellent post. I really found this to much informatics. It is what i was searching for.
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2/9/2023 10:45:19 am
Incredible article! Solar energy is undoubtedly the future of sustainable power generation, and your insights shed light on its immense potential. Thank you for championing a greener, cleaner future for all
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13/9/2023 11:04:27 am
This solar article is enlightening! It clearly explains the benefits of solar energy and its positive impact on the environment. Thanks for spreading awareness about sustainable energy solutions.
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15/4/2024 04:30:41 pm
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Susan's BlogIn which I scribble words about energy, the environment, climate change, and other science things. Views expressed here are my own and do not reflect those of the CDT staff or sponsors. Archives
August 2019
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