The Sun over the ocean.

The Sun over the ocean.

Photo credit: Pixabay

Liquid Fuel: The Quest to Capture Sunshine in a Bottle

In May of 2019, carbon dioxide levels passed 415 parts per a million for the first time in human history. Meteorologist Eric Holthaus took to twitter to articulate the gravity of this development. "Not just in recorded history, not just since the invention of agriculture 10,000 years ago. Since before modern humans existed millions of years ago. We don't know a planet like this," he wrote.

If humanity’s carbon pollution continues to increase, more and more heat will become trapped in our atmosphere, and the consequences for our planet — and the life that it carries — will be grave. If we are to survive as a species, we need to decrease our fossil fuel use.

In order to avoid violent disruptions to our current systems, we are going to need technologies that can efficiently deliver renewable energy on demand, regardless of whether it’s the middle of night, a bright summer’s day, or the dead of winter. This is the problem with current technologies. Although our devices can efficiently generate energy when it is sunny or windy, they can’t cheaply or efficiently store this energy for later use. As a result, our energy resources are depleted when it is cloudy or the air is still.

At the Boma France Campfire, Kasper Moth-Poulsen, a professor of Nanomaterials Chemistry at Chalmers University of Technology in Sweden, underscored this problem and outlined what he’s doing to solve it.

“In just 80 minutes, the Sun provides more energy to Earth than our global society consumes in a full year. It is an almost infinite resource,” he said, “but we’re not good at capturing and using it….so, how can we warm ourselves without generating all this pollution? How can we solve the world’s energy problem?” The solution that Moth-Poulsen came up with is special fluid called a “solar thermal fuel,” and it can store energy from the Sun for well over a decade.

“We have made liquid molecules that can absorb sunlight and transform the light into stored chemical energy. The energy can be stored for more than 18 years at room temperature, and when we release the energy as heat, we can recover the original molecule, which can be used again and again,” he said.

To break down the science, when the molecule is hit by sunlight, it transforms into an energy-rich isomer, which is a molecule that has the exact same atoms, but bound together and configured in a different way. The energy from the Sun is captured between the isomer's strong chemical bonds, and it stays there even if the molecule cools down to room temperature. This isomer can then be stored and released when it’s needed, like, for example, at night or in winter when sunlight is not available for use.

And thanks to a number of developments, when the fluid was initially unveiled, it could already hold 250 watt-hours of energy per kilogram, which is double the energy capacity of Tesla's Powerwall batteries.

But Moth-Poulsen notes that his work is far from over. “If we sit in an office building looking out through a window, the Sun is often too powerful. So we add blinds, curtains, or sunshades to block the heat. During the night, we lose heat through the window, and it’s too cold. If we could integrate our new materials into the window, then perhaps we can level out the daily heat and cooling challenges that we have,” he said.

And Moth-Poulsen and his team are already well on their way to bringing such a technology to life. At the event, he showcased a prototype window that changed from yellow to clear as the molecule within transformed. “Looking ahead, by applying our molecules to windows, cars, or other objects that are out in the Sun, we could level out the temperature variations that objects exposed to sunlight feel,” he said. And since the molecule is made from carbon, hydrogen, and nitrogen, which are three of the most abundant elements on Earth, Moth-Poulsen notes that we would be able to “reduce energy consumption in an emission-free way and, at the same time, increase thermal comfort.”

Although work is still needed to perfect the system, the research has brought us a pace closer to an emissions-free energy system that works year-round, and Moth-Poulsen notes that he is committed to seeing the work through to completion. He paused briefly before he concluded, “the Stone Age didn’t end because they ran out of stones. It ended because better technologies were developed. The fossil fuel age won’t end because we run out of oil and coal. But because we replace fossil technologies with emission-free ones.”


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