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The Stuff Problem

The Stuff Problem thumbnail

How much mined material will we need to build a 100-per-cent renewable world?

The problem with wind turbines, solar panels, ground-source heat pumps and electric cars is that they’re all made of stuff. When people like me make grand announcements (and interactive infographics) explaining how we don’t need to burn fossil fuels because fairly shared renewable energy could give everyone on the planet a good quality of life, this is the bit of the story that often gets missed out. We can’t just pull all this sustainable technology out of the air – it’s made from annoyingly solid materials that need to come from somewhere.

So how much material would we need to transition to a 100-per-cent renewable world? For my new NoNonsense book, Renewable Energy: cleaner, fairer ways to power the planet, I realized I needed to find an answer to this question. It’s irresponsible to advocate a renewably powered planet without being open and honest about what the real-world impacts of such a transition might be.

In this online article, I make a stab at coming up with an answer – but first I need to lay down a quick proviso. All the numbers in this piece are rough, ball-park figures, that simply aim to give us a sense of the scale of materials we’re talking about. Nothing in this piece is meant to be a vision of the ‘correct’ way to build a 100-per-cent renewably powered world. There is no single path to a clean-energy future; we need a democratic energy transition led by a mass global movement creating solutions to suit people’s specific communities and situations, not some kind of top-down model imposed from above. This article just presents one scenario, with the sole aim of helping us to understand the challenge.

How much aluminium, copper, iron and cement would we need?

In October 2014, a joint academic study between researchers from Norway, the US, the Netherlands, Chile and China made an assessment of the main materials needed to build renewable generators: steel, concrete, copper and aluminium.1 They looked at the materials required for renewables to provide 40 per cent of global energy use by 2050, and concluded that this would be feasible within current rates of global resource use.

I’ve taken their figures and attempted to go a step further. How much material would be needed for a transition to a 100-per-cent renewable world, where everyone had access to 13,000 KWh of energy per year? (This is one estimate of the amount of energy needed for an eco-efficient version of a “modern” lifestyle – it’s less than half of the energy currently used per person in the EU). For this calculation, I assumed that 3,000 KWh per person would be provided by non-electric generation (rooftop solar heat collectors, heat pumps, geothermal heat, waste gas, maybe energy crops). I then assumed we would build the following generation sources to provide 10,000 KWh of electricity for nine billion people (these totals all fit comfortably within realistic estimates of the amount that could be sustainably generated from these sources using current technology)2:

If we transitioned to 100-per-cent renewable energy by 2040 – thus giving ourselves a decent chance at avoiding runaway climate change – we would need the materials laid out in the table below to build and maintain this amount of generation.

The table shows that this is a serious undertaking and that we’re cutting things rather fine – particularly with regard to aluminium and copper – but also that the amounts of material required fall within current production totals and so are certainly possible to obtain.3 Once these materials have been extracted once, the metals can theoretically be recycled indefinitely, meaning that we’re talking about a short-term burst of new material use to get everything installed, from which point onwards we’ll be able to get most of what we need from recycling the old turbines, panels and so on.

What if we had to do more mining to achieve this?

Ideally, we would get these materials by diverting production away from less socially useful consumer junk into the sustainable technology that we actually need, so there’d be no net increase in mining. However, what if that isn’t possible? What if our shift to a renewable future requires us to pull an extra four billion tonnes of material out of the ground over the next 25 years? There is no such thing as zero-impact mining; it is one of the most notoriously destructive, poisonous and corrupt industries in the world.

Let’s look at this worst-case scenario. The final amount of raw material produced is just the tip of the extraction iceberg; every tonne of metal or cement requires many more tonnes of rock and ore to be hauled out of the ground in the mining and production process. Making four billion tonnes of copper, aluminium, iron and cement will require 50 billion tonnes of real-life extraction.

However, we need to look at the other side of the equation too. Phasing out fossil fuels over the next 25 years will mean a huge reduction in the amount of oil, coal and gas extracted over that period. Based on IEA projections, shifting to 100-per-cent renewables would avoid the need for around 230 billion tonnes of fossil fuels between now and 2040. Coal, tar sands and heavy oil, like metals, require the extraction of large amounts of extra rock and earth; when all this is added in, our transition would prevent 1,850 billion tonnes of fossil-related extraction up to 2040.

So even if we needed the full 50 billion tonnes of new extraction to build our new electricity generators, we’d still be creating a large reduction in the amount of destructive extractive industry taking place worldwide. We might be able to reduce the damage further by recycling the materials from all the oil and gas rigs, pipelines, and fossil-fuel power stations that we’ll no longer need, providing raw materials for our sustainable alternatives.4

Rare Earth Elements

As well as the high-volume materials, there are also a number of rarer minerals (known as ‘Rare Earth Elements’ or REEs) that we need to watch out for. These include indium, gallium and tellurium, which are used as semi-conductors in some types of solar panel. These metals have important uses in other technologies too (for example, indium is used in solder and flat-screen technologies, and gallium is used in computing components and LEDs), and are relatively rare; this means that there is likely to be a limit to how many solar panels can be made with these particular semiconductors. Luckily, this only affects certain specific designs of panel (not including our familiar black silicon panels),5 and so shouldn’t prevent us from rolling out the amount of solar power we need.

There’s a similar issue with dysprosium, which is used for making magnets in many modern wind turbines. The rarity of this element is likely to constrain the number of turbines that can be made this way. There are, however, alternative ways of making magnets without dysprosium, and so this shouldn’t act as a serious constraint either.

What about the materials needed for the rest of our sustainable transition? A typical ground-source heat pump weighs around 200 kg; air-source units tend to be a little lighter.6 If 200-kg heat pumps were installed – slightly excessively – in three billion buildings around the world, that would require 0.6 billion tonnes of materials. If we also installed three billion solar water heaters, weighing 100 kg each, that would give us another 0.3 billion tonnes. So the rest of our power generation would come in at less than a billion tonnes of material. Even if this required 10 times as much extracted material, bringing our total (when added to electricity generation, above) up to 60 billion tonnes, it would still leave us with a huge material saving thanks to the 1,850 billion tonnes of fossil-fuel extraction that we’re preventing.

A worst-case scenario would involve having enough storage facilities and back-up generators to support our wind and photovoltaic solar generation, making sure that the lights stay on even when the sun sets and the wind drops. Assuming that these facilities required similar quantities of material per KWh as a gas-fired power station, this would add another 0.4 billion tonnes of material, and three billion tonnes of mining.

Electric cars

What about electric vehicles? Well, there are currently more than a billion road vehicles in the world. Currently we are on a path of pure expansion, with the number of cars on the road expected to double in the next 20 years. In 2014, for example, the world manufactured over 80 million new cars, buses and trucks.7

A billion vehicles are probably enough. If distributed more fairly around the world, with the priority on buses and car-sharing schemes, they are likely to give us all the mobility we need. Consider, for example, that cities considered to be well served with buses such as London, Rio and Hong Kong contain between 650 and 1,700 buses per million inhabitants.8 If we decided to err on the side of caution and provide 2,000 buses per million people globally, that would require around 20 million buses. Add in a few billion bicycles (most of which probably already exist) and we’ll have sorted out most people’s daily transport needs. The remaining 980 million vehicles should then be enough to plug the global transport gaps as shared cars, taxis, and trucks for freight.

So what if, instead of doubling the number of vehicles globally in the next 20 years, we instead gradually replaced the existing fleet with renewably powered vehicles? This would require no increase in manufacturing overall, just a change in what we manufactured and where. We could even provide a large amount of the necessary raw materials by recycling old fossil-powered vehicles at the same rate as clean-energy vehicles emerge from the factories.

The point is that a genuine transition to a sustainable transport system wouldn’t require an increase in manufacturing, but a redirection of existing manufacturing. This would need a significant shift from our current position though; out of the 80-90 million vehicles currently manufactured per year, only 200,000-300,000 are fully electric.9

Of course, we should check in with the worst-case scenario too: what if we ended up manufacturing a billion renewably powered vehicles in a way that added to global material use? Well, a typical car weighs around 1.5 tonnes; trucks and buses, though smaller in number, are larger, so let’s be cautious and say an average vehicle weighs two tonnes. This would add two billion tonnes onto our material demand, and thus around 20 billion tonnes onto our grand extraction total, bringing it up 80 billion tonnes. This is still far less than the 1,850 billion tonnes of fossil-fuel extraction that we would prevent.

In addition, there are certain elements used in electric cars that we need to be particularly aware of. One of them is copper – a typical electric car contains around 60 kg of copper, compared with 20 kg in a fossil-fuelled car. If we build a billion of these vehicles over 20 years, we’ll need 0.003 billion tonnes of copper per year. This compares with 0.002 billion tonnes per year that’s already being used for manufacturing conventional cars; if we succeed in phasing out fossil-fuel car production and only building clean-energy vehicles, then we’ll only be increasing overall copper demand by 0.001 billion tonnes per year – much of which should be obtainable from recycling old vehicles. In the worst-case scenario, with no recycling, mining the extra copper needed for a billion electric cars would add another nine billion tonnes of mining onto our extraction total,10 still leaving us way below the fossil-fuelled business-as-usual amount.

Rare elements in electric cars

A recent study by Delucchi et al into the material components of electric cars identified a number of rare elements that could potentially limit their growth.11 The first is neodymium, an element used in electric motors and also in the generators of many wind turbines. Maintaining a billion electric vehicles and obtaining a quarter of our energy from wind turbines could exhaust global neodymium supplies in less than 100 years; however, there are alternative ways of building motors and generators without neodymium, which means that this needn’t be a constraining factor.

The second group of potentially problematic elements are rare metals and minerals such as lithium, cobalt, nickel, manganese, phosphorous and titanium. These are used in the rechargeable batteries in electric cars, and potentially in other energy storage systems too. All of these batteries use lithium, combined with other elements. The Delucchi et al study found that cobalt and nickel reserves, in particular, could be rapidly depleted by a mass rollout of electric cars using batteries containing these elements. Using titanium-based batteries would be unlikely to exhaust global titanium reserves but would involve multiplying the rate of extraction of this metal by more than 100 times, which might create practical difficulties. Fortunately, manganese, iron and phosphorous are much more abundant, and so we should be able to make the batteries we need without relying on cobalt, nickel or titanium.

Lithium itself is more likely to be a problem. The Delucchi et al study suggests that a mass rollout of electric cars could exhaust proven lithium reserves within 100 years – not counting the extra lithium that might be needed for improved electricity storage systems in homes and communities. This means that humanity should be able to obtain enough lithium to make the initial transition to an electrified transport system, but to maintain it beyond the second half of the century we’ll need to either get very good at recycling it, find more supplies, or find safe and affordable ways to extract lithium from the oceans (where it is abundant, but dispersed).

Avoiding a colonialist mindset

There’s another serious issue here. This is one of those moments where it’s easy to slip accidentally into a colonialist mindset, when referring casually to ‘reserves’ of minerals ‘available’ to the world. Whether or not those materials are dug out of the ground should not be a decision for someone like me, a white guy typing on a computer in Europe; it should be up to the communities that live in the area concerned and would be affected by the extraction. Although the quantities of lithium required for everyone in the world to have decent access to electrified transport are relatively small when compared to high-volume mined materials like iron or coal, the necessary mines would no doubt loom large in their local landscape. Most of the world’s known lithium reserves are located in Bolivia and Chile. These are real places, inhabited by real people – including Indigenous peoples whose lives, livelihoods and culture are intimately bound up with the land they live on. Will it be possible to obtain enough lithium for an electrified world without trampling over the rights of local communities? If not, then we’ll need to find a different path to our renewably powered future.

New Internationalist



27 Comments on "The Stuff Problem"

  1. ennui2 on Tue, 29th Sep 2015 8:37 am 

    This is all imaginary solutions where everyone collectively decides to move in the same direction. It will never be feasible, politically, to do this.

  2. ghung on Tue, 29th Sep 2015 8:46 am 

    Meanwhile they’re using tonnes of stuff like neodymium for junk like toy drones and battery-powered “personal fans”. We piss so much stuff away on discretionary crap, we deserve to fail.

  3. penury on Tue, 29th Sep 2015 9:32 am 

    Short version “we are so fuc^^^” and by we I mean life as we know it on this planet.

  4. Kenz300 on Tue, 29th Sep 2015 9:48 am 

    Reduce, Reuse and Recycle………

  5. JuanP on Tue, 29th Sep 2015 9:59 am 

    “They looked at the materials required for renewables to provide 40 per cent of global energy use by 2050, and concluded that this would be feasible within current rates of global resource use.”

    That is as far as I got. I refuse to read something written by someone who doesn’t get that we can’t keep producing resources at today’s rates for another 25 years.

    Life is short and I have no time to waste. If you have time to waste then by all means read this crap. I just got back from two hours of weeding, composting, and mulching the herb beds at the garden. I am also leading a composting workshop at one of the community gardens where I volunteer this weekend and will invest my free time preparing for that now. Carpe diem!

  6. efarmer on Tue, 29th Sep 2015 10:16 am 

    We will have to live underground and earth bermed and segway from building up in the air and having to pump in energy to maintain living temperatures. Mr. Mouse with his little mammal carcass lived through the die out of Mr. Dinosaur and at some point we will have to do the same basic ploy. We will toy with all sorts of high technology, and yield a lot of great new technologies in the process, but reducing energy needs will always beat improving energy technologies.

  7. ghung on Tue, 29th Sep 2015 10:31 am 

    efarmer said: “We will have to live underground and earth bermed and segway from building up in the air…”

    Went there; doing that. Our home basically has two sides: One side collects solar energy, the other is built into the hill. Super-insulated roof, originally planned as a green roof, but fire ants (who’ll eat through most anything) put that idea on hold. Anyway, dirt cheap to live in (pun intended,,, sorry).

  8. makati1 on Tue, 29th Sep 2015 10:34 am 

    Book salesman. Got to the 3rd paragraph and quit reading.

  9. rockman on Tue, 29th Sep 2015 11:45 am 

    ghung – But that problem will easily be solved when we’ve established “…fairly shared renewable energy.” Fairly shared? right…just like the world has been fair sharing fossil fuels. LOLLLLLLLLLLLLLLLLLLL

  10. Jerry McManus on Tue, 29th Sep 2015 12:48 pm 

    There is nothing even remotely “eco” or “efficient” about modern lifestyles, which anyone with even a rudimentary grasp of history and/or thermodynamics can see are a bizarre and grotesque anomaly in the 3-million-or-so year history of hominid-like animals on this planet.

    What a cruel and pointless joke to put so much effort into planning for 9 billion people killing the planet as fast as possible.

  11. GregT on Tue, 29th Sep 2015 1:10 pm 

    “So how much material would we need to transition to a 100-per-cent renewable world? ”

    Less material than the Earth naturally renews. Anything that requires non-renewable resources in it’s manufacture, is in of itself non-renewable.

    This ridiculous techno-banter is getting old.

  12. eugene on Tue, 29th Sep 2015 5:09 pm 

    I figure we’re in the stupid phase of solving the problem. Desperation phase follows stupid. It’s called the rude awakening cycle.

  13. makati1 on Tue, 29th Sep 2015 8:10 pm 

    Eugene, and I think we are fast approaching that phase. That 2X4 of reality is in motion and our collective faces are in the way. It’s already being felt badly in Europe and slightly in America. But, the pain of living is everyday life in some countries and has been for most of history.

  14. green_achers on Tue, 29th Sep 2015 9:44 pm 

    “I figure we’re in the stupid phase of NOT solving the problem.”

    Fixed it.

  15. apneaman on Tue, 29th Sep 2015 10:25 pm 

    The only “stuff” that is a problem is the “stuff” between ape ears. Killer Ape, the super apex predator that did not evolve a self regulatory mechanism like the other apex predators. Good luck with that.

    Top Predators Limit Their Own Numbers

    http://www.iflscience.com/plants-and-animals/top-predators-limit-their-own-numbers

    Abstract

    Large ‘apex’ predators influence ecosystems in profound ways, by limiting the density of their prey and controlling smaller ‘mesopredators’. The loss of apex predators from much of their range has lead to a global outbreak of mesopredators, a process known as ‘mesopredator release’ that increases predation pressure and diminishes biodiversity. While the classifications apex- and meso-predator are fundamental to current ecological thinking, their definition has remained ambiguous. Trophic cascades theory has shown the importance of predation as a limit to population size for a variety of taxa (top–down control). The largest of predators however are unlikely to be limited in this fashion, and their densities are commonly assumed to be determined by the availability of their prey (bottom–up control). However, bottom–up regulation of apex predators is contradicted by many studies, particularly of non-hunted populations. We offer an alternative view that apex predators are distinguishable by a capacity to limit their own population densities (self-regulation). We tested this idea using a set of life-history traits that could contribute to self-regulation in the Carnivora, and found that an upper limit body mass of 34 kg (corresponding with an average mass of 13–16 kg) marks a transition between extrinsically- and self-regulated carnivores. Small carnivores share fast reproductive rates and development and higher densities. Large carnivores share slow reproductive rates and development, extended parental care, sparsely populated territories, and a propensity towards infanticide, reproductive suppression, alloparental care and cooperative hunting. We discuss how the expression of traits that contribute to self-regulation (e.g. reproductive suppression) depends on social stability, and highlight the importance of studying predator–prey dynamics in the absence of predator persecution. Self-regulation in large carnivores may ensure that the largest and the fiercest do not overexploit their resources.

    http://onlinelibrary.wiley.com/doi/10.1111/oik.01977/full

  16. makati1 on Tue, 29th Sep 2015 10:42 pm 

    The “renewables” are already in decline…

    “2011 was a turning point for the European giant as it started moving away from nuclear energy (post Japan’s Fukushima nuclear disaster) and began to replace it with renewables. However, wind energy made its foray in Germany well before 2011. Germany started building wind turbines in the mid-1990s and now there are almost 25,000 wind turbines in the country.
    However, the problem now is that a large number of the 25,000 odd turbines have become too old. Close to 7,000 of those turbines will complete more than 15 years of operation by next year. Although these turbines can continue running, with some minor repairs and modifications, the question is whether it makes any economic sense to maintain them?”

    http://oilprice.com/Alternative-Energy/Wind-Power/Germany-Now-Faced-With-Thousands-Of-Aging-Wind-Farms.html

  17. Beery on Wed, 30th Sep 2015 6:13 am 

    Like many here, I feel the author doesn’t get it. Maintaining a system in which we’re still releasing a lot of heat into the atmosphere is suicidal. What we need is to power down – way down. Or we need to drastically reduce the number of people on the planet so that the energy we use individually can remain high without damaging the ecosystem.

  18. Davy on Wed, 30th Sep 2015 6:36 am 

    Beer said “What we need is to power down – way down. Or we need to drastically reduce the number of people on the planet so that the energy we use individually can remain high without damaging the ecosystem.” I am in complete agreement but the question is what do you have when you power down? Any power down will lead to mass die off since this earth can maybe support 1BIL in a hybrid post fossil fuel world and likely 500MIL in a world with most fossil fuels gone. That will be a world with little complexity, technology, and knowledge.

    Those things degrade quickly like a rotting body. What we need to think about is how quickly do we want to go down? A quick descent will leave no one safe from this destructive decay of decline. Do we want to adjust and mitigate a fall? Can we even do that or will competitive ape tendencies like war get in the way.

    The only question I can see is how fast do we want this fall to be. There is no question on the fall. That is baked into the cake at multiple levels. Can we manage a softer fall? That question is profoundly important for billions whose lives hang in the balance. Food insecurity, hunger, and famine are around the corner for rich and poor alike.

  19. penury on Wed, 30th Sep 2015 9:44 am 

    Looking at the U.N. meeting this week, and reading the comments of the world “leaders” it becomes painfully obvious that the only solution that the U.S. will consider is war. Besides none of it is our fault. Its that nasty OTHER that will not accept the U.S. as their true master. (If you dislike that statement, then read Obama’s speech to the U.N.) Read the defense budget passed by the House. War is not the answer unless you believe that you are one of the privileged few who will survice. Read PJR today on “ZeroJedge”/

  20. sunweb on Wed, 30th Sep 2015 9:51 am 

    And then the second generation in 20 years will come from the Magic Wand?
    I have shared this before: These are videos from the industries. Look not at the panels or inverters or batteries or recycled aluminum; look at the massive infrastructure behind these products. And once we have the devices, where will the tools and toys come from that we want the electricity for?
    Solar and wind energy collecting devices have an industrial history. It is important to understand the industrial infrastructure and the environmental results for the components of the solar energy collecting devices so we don’t designate them with false labels such as green, renewable or sustainable.
    This is an essay challenging ‘business as usual’. If we teach people that these solar devices are the future of energy without teaching the whole system, we mislead, misinform and create false hopes and beliefs.
    I have provided both charts and videos for the solar cells, modules, aluminum from ore, aluminum from recycling, aluminum extrusion, inverters, batteries and copper.
    Please note each piece of machinery you see in each of the videos has its own industrial interconnection and history.
    http://sunweber.blogspot.com/2015/04/solar-devices-industrial-infrastructure.html

  21. sunweb on Wed, 30th Sep 2015 9:55 am 

    Equality?
    Solar and wind energy collecting devices are business as usual, if we do not impose constraints on all energy and other natural resource use.

    In addition, without constraints on electrical usage (toys and tools) then the gross energy inequality globally will continue with solar and wind energy underwriting it. (below find Excel spread sheet info) Without constraints on energy use solar and wind devices and their auxiliary accessories are elitist equipment of the entitled.

    There are two critical questions of the energy/electricity that we are requiring. How do we bring more equitable distribution of energy resources? Is this imbalance and the consequent strife our destiny and our demise?

    Secondly, what do we need the energy for? This must be one of the mantras for survival now and tomorrow. Imagine beginning at the earth resources –the mine and the well- and the subsequent flow of these products. This creates a tremendous picture in motion of ’energy’ and resources flowing around the world. It is a Catch 22; we can’t live with it and can’t live presently without it.

    I took the table from this site:
    https://en.wikipedia.org/wiki/List_of_countries_by_electricity_consumption

    I copied it to an Excel spread sheet. I rank ordered the least energy use to the most and then did an accumulation of population from least energy use to most. I could then look at what 50% or 80% of the world’s population used compared to the US of A.

    Caveat: these figures are approximate however, realistic.

    Caveat: These per capita figures are misleading
    because the wealthy get the ’lion’s share.’

    Approximately 50% of the population (approximately 3.5 billion people) use 3.53 kilowatts a day or less. That is 0.0006% of the total used globally.

    Approximately 80% of the population (approximately 5.6 billion people) use 11 kilowatts a day or less. That is 0.0018% of the total globally.

    The USA uses 40.42 kilowatts a day. That is 4.5% of the global population. We are part of the 1% in global electrical energy use. Even that is misleading, because all the products made elsewhere and shipped to the USA add to the electrical (and total energy) available for our consumption.

    See more at: http://sunweber.blogspot.com/2015/07/electrical-constraint-and-inequality.html – See more at: http://newint.org/blog/2015/08/15/material-requirements/?28541030811532721#sthash.2d55pano.dpuf

  22. Baptised on Wed, 30th Sep 2015 11:43 am 

    I like the article. It shows what could be done. But then their is the human aspect of working together as equals, just will not ever happen. It goes with my opion on socialism. It is the best of all human governing, but will never work. Darn Paradox’s.

  23. energyskeptic on Wed, 30th Sep 2015 11:59 am 

    I heard an old Ugo Bardi podcast on Chris Martenson’s show, and was reminded that the reason there is still so much mining, despite the mountains of scrap metal, is that it is cheaper to mine than recycle. In an energy limited world, it isn’t going to be so easy to recycle 750 ton offshore windmills over and over forever. Offshore turbines need to have rare earth metals to lessen energy-intense maintenance offshore. Well, this is such a silly article, no sense writing more.

  24. penury on Wed, 30th Sep 2015 1:43 pm 

    Did anyone notice that Germany seems to be having a problem replacing their old wind turbines. It seems to cost money.

  25. GregT on Wed, 30th Sep 2015 2:02 pm 

    “And once we have the devices, where will the tools and toys come from that we want the electricity for?”

    That would be the 5 ton elephant in the room that everyone appears to be ignoring.

  26. DavidF on Wed, 30th Sep 2015 6:11 pm 

    Well when he said reduce the amount of waste from socially unacceptable junk, and numerous other points on social justice.

    My question is? What is considered junk?

    There are many other points made which are exactly the same.

    Who decides what to build? (dangerous thinking)

    And a utopian mind, there are many simple minded leftist green fanatics who will love this book. But it’s not accurate, I found many holes as many of you did, almost impossible to think this is a solution without stepping on the rights of every single citizen on the planet.

  27. energyskeptic on Fri, 13th Nov 2015 3:44 pm 

    There are so many problems with this I don’t want to waste time on it, but one of the problems is the extremely short lifespan of wind, solar, and offshore wind and marine kinetic devices, around 20 years, compared to 35-40 for coal, nuclear, and natural gas power plants. For example, see this paper on scaling up wind power:
    Davidsson, S., et al. October 2014. Growth curves and sustained commissioning modelling of renewable energy: Investigating resource constraints for wind energy. Energy Policy 73:767–776 http://dx.doi.org/10.1016/j.enpol.2014.05.003

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