Water, light, and air: that’s about all we need to produce the energy of the future. The solution has always been under our noses. We’ve only lacked the means to exploit it. Thanks to determined pioneer researchers, however, things appear on the verge of changing. By pushing the boundaries of the field of solar energy, we’re getting closer and closer to the ultimate goal: to turn the sun into fuel.

Varun Sivaram is a physician, a professor at Georgetown University, and a member of the American think tank Council on Foreign Relations (CFR). On March 2, 2018, he published his book Taming the Sun: Innovations to Harness Energy and Power the Planetwith MIT Press. In the book, Sivaram underscores the importance of innovation in transition to solar, focusing especially on the work of two brilliant researchers: Nathan Lewis and Daniel Nocera.

For decades, the two men have worked tirelessly toward the creation of solar fuel, over time developing innovations like an “artificial leaf” and an “integrated fuel generator.” But after several years of hopes and subsequent disappointments, they’re now closer than ever to their goal.

Beating Nature

The sun rises in California, spraying its light across great fields covered in solar panels. “There are many paths for cheap, zero-CO2 energy,” says Microsoft founder Bill Gates in a video posted on Gates Notes. “What we need to do is fund the wild scientists who are looking at the early stages of these problems.” A few seconds later, the entrepreneur strolls through the verdant alleys of a Caltech park, a Californian university of technology, next to professor Nathan S. Lewis. In his lab, safety glasses over his focused eyes, “Nate” presents his research on solar fuels to Gates. “He’s trying to turn solar energy into liquid fuel,” Gates explains, amazed. “It’s extraordinary… We’re going to beat nature at its own game.”

It’s been some time now since solar panels began to flourish across the roofs of buildings, from the middle of the desert to the orbits of outer space. Faced with the urgency of climate change, more and more scientists, businesses, and even countries are turning toward this renewable, environmentally friendly energy, because the sun is a star with practically infinite potential. “More energy from the sun hits the earth in one hour than all the energy consumed on our planet in an entire year,” Nathan Lewis says. Although it once occupied a niche space in the market, solar has made such gains that it’s now become the cheapest energy source in the world.

Nate Lewis and Bill Gates at Caltech
Credits: Gatesnotes

Except that every evening, the sun sinks away into the horizon, and certain regions like Scandinavia and Alaska receive fewer of its rays than anywhere else in the world. So we need to come up with a method for efficient storage that will allow us to use it perpetually. To meet the need, Nathan Lewis launched an ambitious project more than 15 years ago: to transform the light of the sun into a synthetic chemical fuel. That might seem crazy, but that’s what plants have done with photosynthesis for billions of years.

When these organisms take in air, water, and sunlight, they’re able to convert solar energy into chemical energy. But that’s not all: they can also store it in carbon molecules, like glucose. It’s a complex phenomenon, only possible thanks to symbiosis between the leaf’s parts. If we can reproduce it artificially, it could be the best way to harvest clean, reliable, and abundant solar energy.

To get there, researchers have worked for many years towards creating a solar fuel generator. Its guiding principle of imitating photosynthesis has led to it sometimes being called an “artificial leaf.” A device submerged in water absorbs sunlight using sensors serving as chlorophyll substitutes. The water molecules are then broken down into oxygen and hydrogen through two half-reactions separated by a membrane. Then, catalysts speed up the process slowly, just as enzymes in nature do. By reproducing the reactions taking place in leaves, this biomimetic technology makes it possible to transform solar energy into chemical energy.

Chengxiang Xiang and Erik Verlage experiment with an artificial leaf
Credits: Lance Hayashida/Caltech

However, Caltech’s ambitious researchers won’t stop there. “We want to make it work better than nature itself,” Nathan Lewis says. Their goal, then, is to eliminate natural errors in photosynthesis to focus only on what really interests them: hydrogen production. The miraculous element H, which can be burned like oil or power a fuel cell, is much cleaner than fossil fuels. The new “white gold” shining in the eyes of automobile designers could be a promising opportunity.

Today, there’s still a ways to go. As Lewis explains, obstacles still hinder the development of an integrated fuel generator. Indeed, it must fill four fundamental criteria: it has to be effective, safe, sustainable, and affordable if it ever hopes to be commercially viable. At the moment, researchers are struggling to meet all four criteria at the same time. Imitating nature is a complex task, and it’s not so easy to make a generator’s component parts work as symbiotically as a leaf’s. To make it a reality, scientists have thrown themselves into the quest for clean energy in recent years.

The Artificial Leaf

Professor Daniel G Nocera holds a little rectangular piece of paper in his fingers and lets it go carefully into a transparent container. Thin as a leaf, it’s about the size of a stamp, made up of one dark face and one pink face. He fully immerses the item and shines a bright light on it. “You just put the leaf in the water, light it up… then oxygen comes out of one side, and hydrogen from the other,” the researcher explains in his brick-walled Boston College laboratory. Small bubbles start to escape from both sides of the leaf. The search for a solar fuel could end sooner than we think.

In 2011, this artificial leaf, created by a team of MIT scientists, caused a global stir. Since then, its creator Dan Nocera has become the very incarnation of a new generation of bold scientists, committed to find a solution to our age’s energy issues. But the quest that led to this first landmark attempt began three decades earlier.

1979. The war between Iraq and Iran unleashed the world’s second oil crisis, just over five years after the first one. Faced with soaring prices, the world finally began to take stock of its profound dependence on black gold. The German chemist Michael Grätzel, who taught at the École Polytechnique Fédérale de Lausanne, began then to look into alternative energies. In 1981, he published a pioneering article titled “Artificial photosynthesis: water cleavage into hydrogen and oxygen by visible light.” But gas prices soon stabilized, and due to lack of urgency and funding, the idea was shelved.

It wouldn’t be until the beginning of the 2000s, with the pressing urgency of human survival in the new millennium, that the scientific world turned again towards renewable energies. Around then, Nathan Lewis and his team were among the first to realize that climate change and energy problems were inseparable. “We understood that we couldn’t wait any longer to study it,” he says. The idea of the fossil fuel industry’s devastating effect on the climate had made headway in the minds of several researchers, and the emerging field of solar energy gripped their attention.

The much talked about device
Credits: Lance Hayashida/Caltech

The US Department of Energy, the US Air Force, and private organizations began to subsidize research on renewable energies. Feeling the tide begin to swell, in 2002 Nathan Lewis organized a large work session with his students and colleagues from Pasadena, California. Their starting point was that they needed to develop a carbon-neutral – and therefore non-polluting – fuel. By putting their ideas together, they sketched the blueprints for construction of a solar fuel generator. Using the principle of photosynthesis, it would have five parts: two sensors, two catalysts, and a membrane. Now they had to find the materials to make it – and to make those parts work together.

At the same time, another brilliant chemist set out on the race for artificial photosynthesis. It was Professor Nocera, then teacher-researcher at MIT, who had also been passionate about this idea for several years. In 2009, he founded a startup called Sun Catalytix (bought out in 2014 by Lockheed Martin) and started actively working on a prototype for an artificial leaf. Two years later, he unveiled a revolutionary invention, the first big breakthrough in the field of solar fuel. The charismatic scientist was invited around the world to present his invention, attracting the attention of Indian billionaire Ratan Tata. The two men had big plans for the miraculous solar cell, such as the construction of a power plant in India.

But right away, the first successes were tarnished by problems. As Professor Sivaram notes, “the most delicate part always comes after the discovery in the lab.” The solar “guru” Nocera was slowed to a near halt by high costs and infrastructural problems in commercial development of an artificial leaf. Even now, the development of effective and cheap catalysts remains an obstacle to large-scale production – the reason why this technology is still in experimental stages.

Nocera and Lewis, who had the same professor at Caltech and who are sometimes depicted as rivals, now pursue two distinct goals. While Lewis continues down the hydrogen path, Nocera has shifted his research towards liquid biofuels. And at the rate of their advances, the quest for solar fuel could end much sooner than we expect.

Taming the Sun

Calcutta, January 2017. The Stadel, a three-star hotel in the Maharashtra region, welcomes the fifth edition of Sabic. The organization of this prestigious symposium on inorganic chemistry, in partnership with the Tata Institute of Fundamental Research, puts India once again in position to be a future energy leader. Before an audience of scientists and entrepreneurs from around the globe, Daniel Nocera presents his new invention: the bionic leaf. His team at Harvard has just begun a partnership with the Institute of Chemical Technology in Mumbai, and he finishes his speech with a shocking declaration: “If we’re able to market the bionic leaf, I want it to debut in India.”

The artificial leaf created by Daniel Nocera
Credits: Dominick Reuter

The previous year, the researcher had joined forces with the biologist Pamela Silver, researcher at Harvard Medical School, to develop a new prototype for an even more advanced leaf. “It works with bacteria, which works in concert with the artificial leaf. They capture hydrogen and carbon dioxide to make a liquid fuel,” Nocera explains. Thanks to genetic modification of these microorganisms, the two researches made a breakthrough. As crazy as it seems, their bacteria started producing solar biofuels instead of sugars. This ambitious bionic leaf, which pushes the known boundaries of science, was awarded Discovery of the Year 2017 at the World Economic Forum.

Nathan Lewis, for his part, followed the hydrogen path. In 2015, his team at Caltech discovered a new coating to efficiently protect his integrated generator’s catalysts. From there, they were able to develop the five indispensable parts of the system. For the researchers, there was only one mission left, certainly the most difficult: make them function in harmony. According to Lewis, though, they’re getting close. “If we continue at this rate, we’ll maybe have something in a year or two,” he says confidently. His prototype, no bigger than a fingernail, will have to be tested at large scale and for a long time.

These fuels can make the imagination run wild. Liquid solar fuels generated by these devices could circulate through pipelines, be distributed at “gas” stations, and power cars, planes, and rockets over long distances. They could also power and heat homes and buildings more sustainably. According to Nocera, taming the sun could even lead to a veritable utopia: “We could soon produce our own energy in our garden,” he says, with the rise of what he terms bionic agriculture.

In developing countries, mastering solar energy could have an even bigger impact. For Nocera, who regularly emphasizes the humanist aim of his discovery, the fact that they don’t have an energy “past” makes the much more open to experimentation. For that reason, he puts a lot of faith in them, and it could be that solar fuel is born on the Indian subcontinent, far from Harvard. Indeed, Nocera transferred intellectual ownership of his bionic leaf to the Institute of Chemical Technology in Mumbai in 2017, making his technology accessible to Indian companies wishing to make their own prototypes.

As Sivaram explains, we will need a lot of volunteerism and political vision to support this kind of research. “We need to make this technology affordable by implementing new scientific policies,” Nocera adds. Although the US Department of Energy supports some projects, he doesn’t think this is sufficient yet. It’s not just humanistic virtue that leads the researcher to seduce countries like India and New Zealand. Nocera complains bitterly about the lack of interest in renewable energies by the United States, and he believes that the future will not be found on that side of the globe.

The generators could soon enter their most critical phase: the innovation phase. Lewis, like Nocera, however, seems fairly confident. “We still have a long way to go to reach a commercial generator, but in general, human beings are good at innovating once the invention is out there,” he says. A few years from now, maybe we’ll see massive solar refineries harvesting hydrogen, or perhaps entire forests flourishing with bionic leaves.

In the meantime, Lewis and Nocera are each going their own way, both feeling that the solution is within reach. Other scientific teams around the world are also working to develop these futuristic technologies. If someone succeeds, then we live in a century where humanity will have finally created a cheap, clean, and virtually limitless energy.