Some people call it the “sunrush”: a 25-year period in which solar power has grown exponentially, transforming the technology from rarefied oddity to the world’s fastest-growing energy source.
This surge, which saw 100MW of capacity in 1992 rocket to more than 300GW in 2016, has been largely driven by falling costs, which plunged 86% between 2009 and 2017.
China, the world leader in building and installing solar panels, added a record-breaking amount of capacity last year. The technology is even setting records in the grey UK: at one point last summer even providing more power than the nation’s nuclear power stations.
But with some experts asking whether the cost reduction curve of solar is drawing to an end, there are questions over whether stratospheric growth can be maintained.
And while more energy from the sun hits the Earth’s surface in an hour than humanity uses each year, can today’s silicon-based solar meet our long-term power needs?
To meet these challenges, researchers around the world are racing to explore new materials which can eke out more energy from the sun’s photons and be used more flexibly than today’s panels.
The most abundant mineral on Earth has become the frontrunner, promising more efficient and lighter solar panels, which could even be made semi-transparent for use as windows.
“Perovskite currently has taken the lead among emerging photovoltaic (PV) technologies,” says Varun Sivaram, fellow for science and technology at the Council on Foreign Relations.
His upcoming book on solar says the crystal has made a meteoric ascent in academic circles, describing it as: “a material that could enable manufacture of cheap, highly efficient solar coatings that could be unspooled from a printer much as newspaper is printed.”
One firm born in Oxford, England, is at the vanguard of the race to develop and scale up perovskite for commercial use. Founded in 2010, Oxford PV initially spent years exploring an alternative, dye-sensitive cells.
But Henry Snaith, the firm’s co-founder, changed tack in 2012. “I discovered perovskite could be extremely efficient in PV cells. We realised this was where the real opportunity lay.”
The British- and German-based company’s big idea is to piggyback on the success of silicon, which Chinese manufacturing scale and efficiency has made so cheap.
Perovskite captures energy from a different part of sunlight’s wavelength than silicon, so Oxford PV’s plan is to layer it atop silicon, to maximise electricity generation.
“We find ourselves in a position that we are not fighting a $35bn industry [silicon], we are enhancing it. The idea is use the existing assets. If you do something completely different it will fail. This can complement the existing cell,” said Frank Averdung, the company’s CEO.
Working with a major but unnamed solar panel manufacturer, the firm hopes to have a product ready for market by 2019.
While the price of silicon-based solar panels has fallen from more than $350 per megawatt hour for a largescale farm in 2009 to more than $50 in 2017, some in the sector think such dramatic reductions have come to an end.
Artur Kupczunas, co-founder of Poland-based perovskite firm Saule Technologies, said the cost cuts had bottomed out: “We saw a very rapid fall of the prices. [But] there are technology obstacles [for it] to go down as rapidly as it did since 2013.”
Saule, which has a partnership with US electric car and solar firm Tesla, and is in talks with Japan’s space agency, is developing inkjet printing for its perovksite-based solar modules.
Today it can only print them at A4 size, but the company’s 25-strong team hopes to expand that to one square metre by the year’s end.
Kupczunas is most excited about the prospect of incorporating the solar panels in fabric of new buildings, both in the walls and – because it can be made semi-transparent – as windows.
“You can use it in the whole building,” he said, noting silicon was too heavy for such applications.
Perovskite is what as known as a third generation solar cell. Silicon is first generation, while a group of other rivals including thin film are the second.
Compared to silicon, which needs to heated at more than 1,000C during manufacture for solar cells, perovskite does not need to be processed at high temperatures. That means it is less energy-intensive and is less costly to make.
A typical silicon-based solar cell converts around 21-22% of sunlight into energy, and the material’s limit is 29%. Oxford PV thinks that its approach of perovskite-on-silicon can get that efficiency up to around 25%.
“What it means is out of same cell, you get 20% more power. That is significant,” said Averdung.
Paul Coxon, a physicist in materials science at Cambridge University, thinks that combining silicon and perovskite could be a good way to commercialise the new technology and overcome the limits of the older one.
“No matter how cheap they [silicon-based cells] become that limit [of 29% efficiency] will still apply. As humanity’s need for electricity grows, continuing with this single technology this limit might pose a tricky hurdle to overcome,” he said.
Coxon said the potential for perovskite is huge, and research is growing fast, as evidenced by nearly 4,000 scientific papers being published on it last year alone. However, he expects silicon will continue to dominate in large, utility-scale solar farms, with the new technology used in smaller, constrained spaces.
“I think we may see perovskite cells used in solar tiles in domestic and smaller scales and maybe even in space-based PV arrays,” he said.
Some might question the need for more efficient solar cells, when China has made silicon-based ones so cheap. But experts believe there are still good reasons to ramp up efficiency through materials like perovskite.
Michael McGehee, professor of materials science at Stanford University, said: “As the cost of solar panels has come down over the last 10 years, the situation has arisen where a little more than half of the cost of putting in a collection of panels is the installation itself.
“For that reason, it is highly desirable to improve the efficiency of the panels so that the number of panels that needs to be installed is reduced. Indirectly that lowers the installation costs. That is why continuing to improve the efficiency is still very important.”
Of course, there is no guarantee perovskite will succeed as solar’s new wonder material. Academics and companies repeatedly emphasised to the Guardian that development is at very early stages, and Oxford PV and Saule both have technical and production challenges to overcome.
Other third generation materials are competing too. “Although perovskite is the lab leader, it does have potential drawbacks, and it isn’t the only promising solar material out there. Other approaches – including organic and quantum dot solar cells – come with their own unique advantages,” said Sivaram.
But the biggest obstacles are likely to be financial ones, such as skittish investors who were burned by previous boom-and-bust cycles in clean technology.
Sivaram said: “As long as investors and the solar industry continue to ignore academia, perovskite and other new solar technologies could well remain lab-bench novelties.”
This article is part of a series on possible solutions to some of the world’s most stubborn problems. What else should we cover? Email us at email@example.com