2016-12-08
Stephen Luntz
I've been covering science for a long time. I'm very familiar with technologies that looked hugely exciting, but ended up going nowhere. Others have yielded impressive outcomes, but took far longer than initially expected. But six big announcements in six weeks on the same topic is rare indeed.
Six weeks ago I wrote an article about a paper in Science on what was claimed to be a record efficiency for perovskite solar cells. The following day I got an email from a researcher in a different team asking if I'd like to cover their own paper announcing an even higher efficiency.
In the week after the election I got two media releases from different teams announcing their own progress in this area. And since then I've had one more, along with another paper on a design to squeeze more power out of any sort of solar cell — perovskite included — in locations that have a fair degree of cloud cover.
For serious nerds I'll discuss a bit about the technology in the sidebar, but for the moment I'll explain why I think this really is something to cling to.
What on Earth is perovskite?
The original perovskite is a naturally occurring mineral (CaTiO3) that has no role in solar cells at all. However, this mineral has an unusual crystal shape, one that can be mimicked with lots of different materials, and some of these have been found to be rather good at turning sunlight to electricity. The name perovskite is now used for any crystal with this structure.
All solar cells run into a problem. A single junction can only be suited to picking up light of a particular wavelength (ie colour). You can have one that collects blue light, but it wastes the red, yellow and green entirely. Or one that will capture the red, but gets only a fraction of the potential energy out of the blue and colours in between.
The ideal solution is to form multi-junction cells that stack on top of each other, with the top layer capturing the violet but transparent in other wavelengths, and successive layers attuned to other colours beneath.
The problem with this is not only that making each layer adds to the cost, it is that silicon cells are only really suited to representing the red layer. Other sorts have been made for shorter wavelengths, but some are horrendously expensive.
The great thing about a perovskite structure is that a wide variety of metals can be added to it, and each combination brings its own benefits.
A perovskite crystal is so flexible that if you want to capture a particular part of the spectrum it is just a matter of finding out which particular metals need to be added to the recipe to match what is required. Sometimes the only way we have worked out how to do this is with expensive metals like iridium, but often cheap combinations, such as tin and lead, have done the trick.
Consequently, it should be possible to produce a multitude of solar cells, exquisitely matched to conditions in the location where they are to be used, and each capturing much more of the spectrum than we can currently manage. In most cases, this should involve cheap materials and no need for the high temperature processing that accounts for so much of the price of silicon cells.
Initially the two big obstacles were:
- making the cells a decent size without losing too much efficiency — there is always a dropoff as you scale up, but for early versions this was intolerably large; and
- making them last — many perovskites degrade quickly on exposure to water or air.
But we're well on the way to tackling both of those. Some of the recent versions have proven very resistant to trying conditions, and one of the recent announcements (Australian, by the way) was of records broken for the efficiency of cells of more practical size. We're not there yet. The most efficient scaled up cell is still only about two thirds of the efficiency we need, but given that a year ago we were closer to one third, there's little reason to think we have long to wait.
What's the big deal?
Anyone even halfway 'green' would see developments in solar power as good news, but it's easy to miss how important this could be.
It's hard to know just how cheap perovskite cells could be, but the answer almost certainly is very cheap indeed. If some of the work these teams are promoting can be brought to fruition we are likely to see solar-produced electricity sold profitably for prices of US$20-$40 per MWh everywhere outside of northern Europe, Antarctica and a few bits of North America.
This is cheaper than almost any electricity produced with fossil fuels — even when they don't have to pay for the pollution they emit, and the original cost of building the plant has long been paid off.
In other words, outside far northern latitudes or unusually cloudy places, coal or gas fired power stations would be operating at a loss during most daylight hours, since they would need to sell for less than this to keep operating. In rare circumstances coal-fired power stations could try to stay open by making big profits at night, but generally speaking this will be impossible too. The battle to power most of the world at night will be between batteries holding stored solar power and gas fired plants that can power down during the day.
Moreover, this vision could be coming very, very fast. Oxford Photovoltaics, the company spun off by Oxford University to commercialise the research covered in the Science paper, has bought a German production line and expects to be churning out prototype cells in 2017. Their goal of having perovskite cells on the market in 2018 may be ambitious, but it doesn't seem crazy. Those first cells probably won't undercut silicon by much on price, but it won't take long for prices to fall. The fact that so many teams are producing their own versions means that it will be very hard for patent holders to maximise profits by keeping prices relatively high.
This would completely throw energy predictions out. The International Energy Agency has recently brought forward the date when they think coal consumption will peak to 2020, but they still expect the downslope to be relatively gradual. It may seem arrogant of me to tell the experts they are wrong, but given that the IEA has been underpredicting the growth of solar by orders of magnitude for at least 15 years, I don't feel ridiculous doing so.
It seems to me that when solar can be installed at a price coal can't match, this will actually happen, and coal plants will close at a staggering rate. I can't see any reason why there will be any coal plants operating by 2030 outside a few countries — notably Poland — that combine low sunlight with abundant local coal.
Climate change remains the biggest problem we face. Two thirds of emissions are from sources unrelated to electricity production, including metallurgical coal, which won't be affected by this. Gas at night will keep emissions from the sector at significant levels as long as it can beat stored solar on cost. But the problem will look a lot more manageable with such a big chunk taken out of it.
Not just climate change
The benefits reach far beyond slowing global warming. Start off with the hundreds of thousands who die each year from coal-induced air pollution. Then there is the effect on global poverty. Already picosolar lamps are bringing light to millions, but perovskite versions could give enough power to do far more for the same price. Since the sunniest parts of the world are mostly also the poorest, this will see a non-trivial transfer of wealth from the rich world to the poor, where electricity now will be cheapest.
And then there is the effect on the politics. On a global scale oil and gas are doing more damage to our public debate than coal, but the billions funneled into right-wing causes by coal barons have certainly had a toxic effect. Without the belief that pollution measures, not price, were killing coal jobs it's unlikely Trump would have won Pennsylvania.
Already solar installations employ more people in the US than coal, but that could ramp up fast, with hundreds of thousands of Americans whose livelihood comes from fighting climate change, not causing it. Even if some of them are racists or misogynists, that may not be an electorate Republicans find so easy to tap. And maybe, just maybe, some people are going to notice that Republican intransigence has caused a lot of the manufacturing jobs that could have been located in the US to move elsewhere instead, above and beyond low labor costs.
That production line Oxford Photovoltaics bought? It's in Germany. And just as Brexit probably killed the chances of future perovskite panels being made in the UK, despite much of the research being done there, Trump is going to ensure America's slice of the pie is a lot smaller than it could have been. That could matter in four year's time.
Perovskite won't stop the spiraling racist attacks, or save queer kids from “conversion therapy' (read torture) or give women control of their wombs. But not only might it mean humanity gets to stick around a bit longer to address these issues, it might play a small part in discrediting the people responsible.
Stephen Luntz is a psephologist working with the Victorian Greens who also writes for IFLS.