Why Solar Panels Should Go From Rooftops to Mountaintops

A new study finds that installing solar panels on snow-covered mountains could help close the gap between demand and production during the winter months.
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Tourists face a sea of mist engulfing the Alps from Moleson peak, Western Switzerland, on September 26th, 2015.

One potential advantage of mountaintop solar panels is that mountaintops in the Swiss Alps often peek through cloud cover.

Imagine an array of solar panels. Did you picture it in the middle of a dry and dusty desert? Or on a rooftop in California? That's where the majority of solar installations around the world are constructed today, but a new study by researchers in Switzerland, published Monday in Proceedings of the National Academy of Sciences, finds that solar panels on snowy mountaintops could generate the same amount of energy as urban installations with much less surface area.

The study stems from the alpine country's decision to phase out nuclear power, according to lead author Annelen Kahl, a postdoctoral researcher at École Polytechnique Fédérale de Lausanne in Switzerland. As part of its Energy Strategy 2050, Switzerland banned new nuclear plants and plans to phase out existing ones, which currently generate 35 percent of the country's energy. As those plants shut down, any energy they produced will need to be generated by renewables. Right now, wind and solar provide less than 5 percent of the country's power, and so researchers at EPFL went looking for innovative ways to increase the proportion of renewables in Switzerland's energy mix.

Even though the cost of solar energy has dropped dramatically in recent years and energy storage technology has improved, there are still many hurdles to replacing non-renewable energy sources with solar in particular—including a mismatch between peak energy production, which occurs during the summer months, and peak energy demand, which typically occurs during the winter.

Kahl and her colleagues wondered if installing solar panels in Switzerland's mountainous regions, which cover more than half the country, might help close the gap. Theoretically, solar panels at higher elevations can capture more of the sun's energy because less solar radiation is absorbed by the thinner atmosphere at high altitudes. There are other potential advantages of mountaintop arrays over urban installations as well: Mountaintops in the Swiss Alps generally peek through the wintertime cloud cover, and snowcapped peaks can reflect some of the solar energy hitting the ground back up at mountaintop solar panels. But until now, there was not enough data available to quantify the potential of solar panels at high elevations.

Kahl, who has a view of a small solar array from her office in Davos, used data collected hourly by satellite instruments on the amount of solar radiation hitting Switzerland and on the reflective potential of its snow-covered regions over a six-year period. The analysis showed that the strategic placement of solar panels in high-elevation, snow-covered regions could cut the wintertime energy deficit in half. And that's likely an underestimate, according to Kahl. The resolution of the satellite data was relatively coarse: Each pixel covered an area of a few square kilometers, which means that snow cover, and thus the amount of solar energy reflected back up at solar panels, could vary within each pixel.

"If you know your terrain well, you could probably choose your installation locations for the most optimal placement within that pixel," Kahl says, "so our results are conservative." This particular study didn't look at the impact of temperature, but Kahl says that cold temperatures can also improve a panel's performance. "A solar panel produces more electricity if it's in a cold environment," she says.

Of course, Kahl notes, the study doesn't address all of the potential hurdles to installing solar arrays in the mountains, including social acceptance, economics, logistics, and existing infrastructure—because the cost of installing solar panels in remote, rugged terrain and getting that energy onto the grid could outweigh the benefits. But Kahl is cautiously optimistic.

"In the Alps, for instance, there is already a lot of existing infrastructure that could be used to install photovoltaic panels on top of them," she says. "We have a lot of hydropower plants that already have road access, they have grid access, so the electricity could immediately be fed into the electricity network. It's important for people, investors, politicians to know that this possibility is out there."

This particular study was focused on Switzerland, but other mid-latitude, mountainous countries with similar conditions might also benefit from solar arrays on snow-capped peaks—especially in the wake of the United Nations' latest dire climate report, which found that the world has just a few short years to phase out fossil fuels or suffer catastrophic climate change.

*Update—January 8th, 2019: This post has been updated with an accurate measurement of the resolution of the satellite instruments.

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