Can Solar See the Light with Perovskite?

One of the big questions for humanity’s future is: how will we supply enough clean and plentiful energy to sustain a growing global population? At face value, the big question has a simple answer: solar. In theory, the world’s demand could be met by just one thousandth of the sun’s energy landing on Earth. In practice, solar accounted for 1.1 percent of global power generation in 2015. To narrow the gap between theory and practice, we need to look at next-generation technologies that can take solar into the mainstream. And the technology with the greatest potential is perovskites.

How pressing is the problem? Very. The global energy industry is at a tipping point.

BP’s 2016 Energy Outlook showed that global GDP is expected to more than double by 2035. Driven by emerging economies in Asia — with China and India projected to account for half the rise in GDP — this growth means that more energy will be required. In fact, BP expects a 34 percent increase in energy consumption by 2035. This research has plenty of support. The International Energy Agency’s most recent World Energy Outlook predicts that industrialization and urbanization of areas in Asia, Latin America and MENA is likely to result in a 30 percent rise in global energy demand by 2040.

At the same time, ‘peak fossil fuels’ is looming — thanks to dwindling reserves, the success of renewable energy and consumer and governmental pressure to avert climate change. Demand for fossil fuels will plateau, and it may come sooner than you think. Bloomberg New Energy Finance (BNEF) says as soon as 2025.

However, according to BP, 86 percent of global energy demand was met by fossil fuels in 2014. That’s a considerable majority. So what will we replace that power source with? Almost every commentator worth their salt is pointing to solar. BNEF expects 68 percent of new electricity capacity to come from solar over the next 25 years.

The Problem

Solar is a success story. An estimated 16 GW of solar capacity was installed globally in 2010, which soared to a whopping 75 GW last year (roughly equivalent to the entire U.K. power grid). Largely this is due to plummeting silicon costs — down from $475/kg in 2008 to less than $20/kg in 2015. This has meant cheaper tariffs too — as low as $0.03 per KW/h in Dubai. Around the world, solar has been catapulted into the limelight as the renewable generation technology of choice.

However, silicon costs can only go so low, and manufacturers are encountering the law of diminishing returns as millions invested in improved manufacturing processes eke out smaller and smaller gains. An average mass-produced cell of 17 percent efficiency now costs around $0.30 per watt based on a 4.5 W cell. The standard silicon cell has probably reach its limit.

At the same time, early subsidy support has been scaled back or withdrawn in many places — such as the U.K.’s feed-in tariffs scheme. 2016 was a record-breaking year for the technology with half a million solar panels installed every day. Solar installations have continued — especially in sunnier parts of the world. But the pace in places like the U.K. has reduced. Government data shows that 4.1 GW new solar capacity was installed in 2015, which was reduced to just 1.8 GW in 2016.

Overall, solar is a technology teetering on the edge of self-reliance: it can just about stand on its own two feet, but it would be steadier on them if subsidies had continued a little longer or a technological breakthrough came along. With green subsidies too often used as a political football (despite the fact that, globally, fossil fuels received $0.5 trillion in 2014 — four times more than renewables), the safer bet is probably on the tech.

The Solution

That breakthrough could be many things — and will most likely come from a mix of technologies. Smart grids will support decentralized generation and storage will iron out peaks and troughs in renewable supply. But, if one thing is certain, it’s that the future will bring new, not-yet-imagined technologies to tear up the rulebook. For now though, there’s a breakthrough innovation that’s close to commercialization — one that can unlock the true potential of solar: perovskites.

Perovskites are mineral structures with superior photovoltaic properties. They capture more of the light in the electromagnetic spectrum than silicon, meaning they can harness far more energy from the sun than current technology.

The solar efficiency of cells using perovskite increased from 3.8 percent in 2009 to 21 percent in 2017. Similar strides for silicon took decades, making perovskite the fastest improving solar technology developed to date. Concerns around durability and stability when in contact with moisture proved an early barrier, but recent indications are that these have been overcome, and now perovskite is ready for its time in the sun.

However, there’s no reason to pit perovskites against silicon. Because perovskites can capture different parts of the light spectrum, huge gains can be made by combining the technologies in tandem perovskite-silicon cells. This means building on the great manufacturing strides made in silicon to date and utilizing the supply chains that have taken years and millions of dollars to establish.

Adding a perovskite layer to silicon cells does introduce an additional manufacturing cost, however this is more than offset by the gains made in cell efficiency.

For example, in 2015 the average installation cost for a PV system in the U.S., weighted across utility, commercial and residential rooftop solar, had an average cost per watt of $1.88. Adding a thin-film perovskite layer pushes the cell cost up slightly. However, this extra layer increases the efficiency by at least 20 percent. That’s a cost per watt reduction of $0.27, 15 percent. That may not sound like a lot but at scale the numbers are impressive. At 1 GW, a saving of $0.27 per watt equates to a savings of $270 million.

Put that in the context of the 75 GW of capacity installed in 2016 worldwide. The savings would be counted in the billions.

So — we find ourselves at two tipping points. On the one hand, we’re on the cusp of peak fossil fuels; a historic moment if we can find the right answer to the question of what comes after. That depends on the second tipping point — the answer can and should be solar, which teeters on the edge of true self-reliance. Having just about exhausted the incremental improvements to current solar technology, we need a technological breakthrough. That’s why we need perovskites.