Advanced solar panels still need to pass the test of time

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It must be tough to be a solar panel. They're consistently exposed to sun, heat, and humidity-and the panels installed today are expected to last 30 years or more.

But how can we tell that new solar technologies will stand the test of time? I'm fascinated by the challenge of predicting how new materials will hold up in decades of tough conditions. That's been especially tricky for one emerging technology in particular: perovskites. They're a class of materials that developers are increasingly interested in incorporating into solar panels because of their high efficiency and low cost.

The problem is, perovskites are notorious for degrading when exposed to high temperatures, moisture, and bright light ... all the things they'll need to withstand to make it in the real world. And it's not as if we can sit around for decades, testing out different cells in the field for the expected lifetime of a solar panel-climate change is an urgent problem. The good news: researchers have made progress in both stretching out the lifetime of perovskite materials and working out how to predict which materials will be winners in the long run.

There's almost constant news about perovskite solar materials breaking records. The latest such news comes from Oxford PV-in January, the company announced that one of its panels reached a 25% conversion efficiency, meaning a quarter of the solar energy beaming onto the panel was converted to electricity. Most high-end commercial panels have around a 20% efficiency, with some models topping 23%.

The improvement is somewhat incremental, but it's significant, and it's all because of teamwork. Oxford PV and other companies are working to bring tandem solar technology to the market. These panels are basically sandwiches that combine layers of silicon (the material that dominates today's solar market) and perovskites. Since the two materials soak up different wavelengths of light, they can be stacked together, adding up to a more efficient solar material.

We're seeing advances in tandem technology, which is why we named super-efficient tandem solar cells one of our 2024 Breakthrough Technologies. But perovskites' nasty tendency to degrade is a major barrier standing in the way.

Early perovskite solar cells went bad so quickly that researchers had to race across the laboratory to measure their efficiency. In the time it took to get from the area where solar cells were made to the side of the room where the testing equipment was, the materials basically lost their ability to soak up sunlight.

The lifetime of perovskite materials isn't nearly this fleeting now, but it's not clear that the problem has been entirely solved.

There's been some real-world testing of new perovskite solar materials, with mixed results. Oxford PV hasn't published detailed data, though as CTO Chris Case told Nature last year, the company's outdoor tests show that the best cells lose only about 1% of their efficiency in their first year of operation, a rate that slows down afterwards.

Other testing in more intense conditions has found less positive results, with one academic study finding that perovskite cells in hot and humid Saudi Arabia lost 20% of their efficiency after one year of operation.

Those results are for one year of testing. How can we tell what will happen in 30 years?

Since we don't have years to test every new material that scientists dream up, researchers often put them through especially punishing conditions in the lab, bumping up the temperature and shining bright lights onto panels to see how quickly they'll degrade.

This sort of testing is standard for silicon solar panels, which make up over 90% of the commercial solar market today. But researchers are still working out just how well the correlations with known tests will transfer to new materials like perovskites.

One of the issues has been that light, moisture, and heat all contribute to the quick degradation of perovskites. But it hasn't been clear exactly which factor, or combination of them, would be best to apply in the lab to measure how a solar panel would fare in the real world.

One study, published last year in Nature, suggested that a combination of high temperature and illumination would be the key to accelerated tests that reliably predict real-world performance. The researchers found that high-temperature tests lasting just a few hundred hours (a couple of weeks) translated well to nearly six months of performance in outdoor testing.

Companies say they're bringing new solar materials to the market as soon as this year. Soon we'll start to really see just how well these tests predict new technologies' ability to withstand the tough job a commercial solar panel needs to do. I know I'll be watching.

Related reading

Read more about why super-efficient tandem solar cells made our list of 10 Breakthrough Technologies in 2024 here.

Here's a look inside the race to get these next-generation solar technologies into the world.

Perovskites have been hailed as the hot new thing in solar for years. What's been the holdup? In short: stability, stability, stability.

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