After the (ahem) roaring success of my essay on battery recycling, I bring you the hotly anticipated SOLAR PANELS edition of "Things whose issues with recycling reflect really badly on the renewable energy industry". To cover:
What are solar panels made of? I'm only looking at photovoltaics here (PV; solar thermal is something else). Multicrystalline silicon is the most common PV technology, followed by monocrystalline silicon (same material but processed to have no grain boundaries - slightly more efficient, more expensive). Crystalline silicon (c-Si) PV has been providing power since the 1970s, or even before if you count the ones powering spacecraft. Then there's 2nd-generation PV, which only became commercialised in the last decade or so - thin films like CIGS (copper indium gallium selenide) and CdTe (cadmium telluride, 'Cad-Tel'). Then 3rd-generation solar, which is still on the lab bench - perovskites and organic polymers and all sorts.
Then when you ask about the embodied environmental impacts, you find another perspective entirely: OK, that's a lot of information, but the point is most of the environmental impacts come from processing the silicon. And no wonder: it takes fantastic amounts of energy to produce silicon from sand, and to purify it to solar-grade. (Remember though, a solar panel in the UK can generate as much energy as it took to make it in 3 years, and will keep generating for around 30 years.) Metals depletion doesn't follow the same trend as the other impact categories, being mostly due to the inverter and (copper) cabling. [2] So what are solar panels made of? By mass, mostly glass. By value, a good deal silver. By embodied environmental impacts, mostly silicon and associated processing. Why do we need to recycle them? Considering the 30-year lifetime of solar panels, and the fact that production only really started accelerating in the 2000s, there aren't a lot of dead panels around yet. 43,500-250,000 metric tons by the end of 2016 - but this could grow to 6 million tons per year by 2050 [1, p.11]. Admittedly that's small compared to the current production of 20-50 million tons per year of electronics waste - but that is essentially what solar panels are. Metals, plastics and glass do not easily biodegrade, and some components (especially in thin-film panels) are toxic. Imagine instead, if those resources could be used again - how much extraction of finite resources could be avoided! It's not so much an issue of running out, but depleting reserves so that more and more money needs to be pumped into mining, raising the price of those commodities. But silicon is one of the most abundant elements on Earth - do the arguments about resource depletion really apply to it? An interesting anecdote from the early days of solar power (and don't take it more seriously than it deserves) was that waste silicon from the computing industry would be a cheap source of material from which to make solar panels. And though electronics-grade silicon is higher purity than solar-grade, demand for solar panels quickly outstripped supply from 'mining' electronics production waste, silicon started needing to be produced just for solar panels, and cheap solar panels stayed a very brief dream. (Notwithstanding the 8x price reduction in the past decade.) And now something similar might be happening with CdTe - cadmium, though too rare to mine for on its own, is a highly toxic by-product of zinc mining. Producing CdTe solar panels is an efficient way of stabilising toxic cadmium - but if the demand for CdTe panels increases, for how much longer will that be true? While manufacturing and processing silicon is the most environmentally burdensome aspect of solar panels, I suspect recycling silicon will not do much to relieve that burden. I can't say that for sure, because there are currently no solar panel products that boast of being made from recycled silicon. Repaired/reused solar panels are a different matter - if the cells are intact, then fixing the junction box or back plate or whatever has gone wrong is a fantastic thing to do [1, p.79] - but if the cells have been scratched or in any way damaged, the silicon needs to be etched off and it looks like it gets downcycled into applications other than new solar panels, if at all. The real concern from a resource depletion point of view are the metals used to make the electronics (inverter) and cabling for solar panels. Because this is quite an abstract problem, here's a tenuously relevant, recent piece of news to bring the point home: Fatal dam breach in Brazil leaves hundreds missing Amanda Jasi and Adam Duckett 2019-01-28 This particular dam was used to hold back tailings from mining iron ore. (Minerals occur at low concentrations in the earth, so a lot of earth gets processed and needs to be dumped somewhere once the minerals have been extracted.) And though there were flaws in the design and management in this case, dam breaches and long-term seepage of toxins from mine tailings into water sources are recurring problems. A quote from the article: "...as demand for resources increase and the grade of ores being processed diminish, the volume of tailings is set to increase." So, these are the reasons for recycling solar panels:
What's the state of solar panel recycling today? This is a strangely difficult question to answer. There are sources that boast of recycling processes that recover materials at impressive rates. Here's one: And more: [3], [4]. But it appears that just because those processes exist, doesn't necessarily mean they're being used. Some reckon the glass and aluminium (which make up the bulk of the solar panel) are decontaminated and then recycled to make new glass and aluminium products, with the rest being incinerated [1], [5]. Some reckon most panels are entirely landfilled [6]. The state of play at the moment:
What about the future? Installed solar capacity is well over 200 GW globally and expected to rise to 4500 GW by 2050 [1, p.11]. That's a lot of solar panels getting decommissioned along the way, which is GOOD NEWS for achieving economies of scale in recycling. If you spend any time looking at life cycle analysis, you come to appreciate how quickly technological processes change (and how quickly all your source data become out-of-date, grrr). The manufacture of multicrystalline silicon solar panels, for example, has become much more environmentally benign over the years. Two big factors:
When it comes to 3rd-generation solar, new recycling processes need to be invented. Hopefully they'll take the opportunity to design recyclability in from the start. For silicon solar panels, it doesn't look like there's a lot technically that's stopping a high percentage of their mass getting recycled. The problems are in collecting them, having enough recycling capacity to process them, and financing the operations. Regulations have a part to play, in mandating both recycling itself and the setting aside of funds to do so, and the EU is leading the way with its WEEE directive. For the more classical economics-inclined, a carbon tax to 'internalise the externalities' [3] could incentivise both recycling and reducing the energy intensity of PV production processes. (The greater cost of solar panels could be offset by higher prices for fossil-fuelled electricity, but care would be needed not to overly burden the poor and small businesses with high electricity bills - my radical preference is for all tariffs with above-zero standing charges to be abolished.) At the end of the day, PV recycling is not (yet) doing that much for the embodied environmental impacts of producing and processing silicon. What recycling does is reduce landfill contamination and reduce resource extraction for the materials that do get recycled. To tackle the silicon impacts problem, what's needed is more energy-efficient and materials-efficient production processes, indeed for new types of solar panels too, and repair and reuse at end-of-life. A danger with second-hand panels is the risk of polluting countries with less developed waste collection infrastructure [6]. This is something that needs to change, for the sake of the people living in those countries, and the oceans and wherever else runaway trash ends up. There's a lot of optimism out there, even from [6] (an excoriating indictment of an industry the writer supports deep down, after my own heart). If you've read up to this point, well done and THANK YOU! And if you have questions, please ask away in the comments section below. Further Reading
[1] End-of-Life Management - Solar Photovoltaic Panels IRENA (International Renewable Energy Agency) [2] A Comparative Life Cycle Assessment of PV Solar Systems Kristine Bekkelund 2013-10-08 [3] End-of-life PV: then what? - Recycling solar PV panels Kari Larsen 2009-08-03 [4] Can Solar Panels Be Recycled? Tom Schoder May 2018 [5] Europe's first solar panel recycling plant opens in France Geert De Clercq 2018-06-25 [6] If Solar Panels Are So Clean, Why Do They Produce So Much Toxic Waste? Michael Shellenberger 2018-05-23 [7] Current and future priorities for mass and material in silicon PV module recycling Olson, C. L.; Geerligs, L. J.; Goris, M. J.A.A.; Bennett, I. J.; Clyncke, J. 2013-10-15
6 Comments
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14/4/2022 03:22:29 pm
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8/7/2023 06:52:26 am
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4/8/2023 01:56:32 pm
Brilliant article on solar panels! The information provided was clear and concise, making it easy to grasp the benefits of solar energy. Thanks for shedding light on this eco-friendly and cost-effective solution for a greener future
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30/8/2023 03:34:33 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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