Scientists are Trying To Bottle Solar Energy and Turn It Into Liquid Fuel

“A solar thermal fuel is like a rechargeable battery, but instead of electricity you put sunlight in and get heat out.”


Professor Kasper Moth-Poulsen holding a tube containing the catalyst in front of the ultra-high-vacuum setup that was used to measure the heat release gradient in the molecular solar thermal energy storage system.Johan Bodell

By: Wayt Gibbs

What if we could bottle solar energy so it could be used to power our homes and factories even when the sun doesn’t shine?

Scientists have spent decades looking for a way do just that, and now researchers in Sweden are reporting significant progress. They’ve developed a specialized fluid that absorbs a bit of sunlight’s energy, holds it for months or even years and then releases it when needed. If this so-called solar thermal fuel can be perfected, it might drive another nail in the coffin of fossil fuels — and help solve our global-warming crisis.

Unlike oil, coal and natural gas, solar thermal fuels are reusable and environmentally friendly. They release energy without spewing carbon dioxide and other greenhouse gases into the atmosphere.

“A solar thermal fuel is like a rechargeable battery, but instead of electricity, you put sunlight in and get heat out, triggered on demand,” says Jeffrey Grossman, who leads a lab at MIT that works on such materials.


On the roof of the physics building at Chalmers University of Technology in the Swedish city of Gothenburg, Kasper Moth-Poulsen has built a prototype system to test the new solar thermal fuels his research group has created.

As a pump cycles the fluid through transparent tubes, ultraviolet light from the sun excites its molecules into an energized state, a bit like Dr. Jekyll transforming into Mr. Hyde. The light rearranges bonds among the carbon, hydrogen and nitrogen atoms in the fuel, converting a compound known as norbornadiene into another called quadricyclane — the energetic Mr. Hyde version. Because the energy is trapped in strong chemical bonds, the quadricyclane retains the captured solar power even when it cools down.

The energy system works in a circular manner. First, the liquid captures energy from sunlight, in a solar thermal collector on the roof of a building. Then it is stored at room temperature. When the energy is needed, it can be drawn through the catalyst so that the liquid heats up.Yen Strandqvist

To extract that stored energy, Moth-Poulsen passes the activated fuel over a cobalt-based catalyst. The Hyde-like quadricyclane molecules then shapeshift back into their Jekyll form, norbornadiene. The transformation releases copious amounts of heat — enough to raise the fuel’s temperature by 63 degrees Celsius (113 degrees Fahrenheit).

If the fuel starts at room temperature (about 21 degrees C, or 70 degrees F), it quickly warms to around 84 degrees C (183 degrees F) — easily hot enough to heat a house or office.

“You could use that thermal energy for your water heater, your dishwasher or your clothes dryer,” Grossman says. “There could be lots of industrial applications as well.” Low-temperature heat used for cooking, sterilization, bleaching, distillation and other commercial operations accounts for 7 percent of all energy consumption in the European Union, Moth-Poulsen says.

A solar thermal fuel could be stored in uninsulated tanks inside houses or factories — or perhaps piped or trucked between solar farms and cities. Very little of the fuel or the catalyst is damaged by the reactions, so the system can operate in a closed loop, picking up solar energy and dropping off heat again and again. “We’ve run it though 125 cycles without any significant degradation,” Moth-Poulsen says.


Moth-Poulsen has calculated that the best variant of his fuel can store up to 250 watt-hours of energy per kilogram. Pound for pound, that’s roughly twice the energy capacity of the Tesla Powerwall batteries that some homeowners and utilities now use to store electricity generated by solar panels.

“I’m very excited by what Kasper is doing,” Grossman says of the research. After a burst of work on norbornadiene fuels in the 1970s, he says, chemists were stymied. The fuels kept breaking down after a few cycles. They didn’t hold their energy very long, and they had to be mixed with toxic solvents that diluted the energy-grabbing fuel. Moth-Poulsen “has gone back to that molecule and is using state-of-the-art tools to fix it,” Grossman says.

The new results, published in a series of scientific papers over the past year, have caught the attention of investors. Moth-Poulsen says numerous companies have contacted him to discuss the potential for commercialization.


For all the promise of solar thermal fuels, years of development lie ahead. “We’ve made a lot of progress,” Moth-Poulsen says, “but there is still a lot to figure out.”

A crucial next step will be to develop a single fuel that combines the best characteristics of the many fuel variants the Chalmers team has developed — including long shelf life, high energy density and good recyclability.

Wei Feng, who leads a research group working on solar thermal fuels at China’s Tianjin University, points to solvent-free operation as another “big challenge for future commercialization.”

Moth-Poulsen’s prototype fuels are made via common industrial processes and from widely available industrial agents, including derivatives of acetylene. But it’s unclear how much a commercial version of the fuel would cost.

One important factor in the cost will be the fuel’s efficiency, which currently is quite low. The prototype fuels respond only to the shortest wavelengths of sunlight, including ultraviolet and blue, which account for just 5 percent of the solar energy available. Moth-Poulsen says he’s working to extend the fuel’s sensitivity to include more of the spectrum.

He’s also aiming to break his own record of a 63-degree C temperature increase. When that heat is added to water that has been preheated to 40 degrees C or more by conventional solar collectors, he says, “That’s just enough to boil water into steam.” The steam could then drive turbines to make electricity. But with more tweaks to the chemical structure, he says, “I think we could push [the temperature increase] to 80 degrees C or higher.” For electricity generation, hotter is better.

“When I started, there was really only one research group working on these kinds of systems,” the 40-year-old Moth-Poulsen recalls. But progress has drawn others to the challenge. “Now there are teams in the U.S., in China, in Germany — about 15 around the world,” he says.


After Hurricane Maria, Puerto Rico May Shift To 100% Renewable Energy

After Hurricane Maria left many on the island without electricity for nearly a year, politicians are leaning toward a more sustainable and resilient way to power Puerto Rico.

Photo: 2pluscolors/iStock

BY: Adele Peters

After Hurricane Maria decimated Puerto Rico’s power grid, causing the longest blackout in U.S. history, it ignited a new push for renewable energy–a solution that could be more resilient in future storms and avoid the emissions that are making hurricanes worse. Now, lawmakers want to make it official: Today, the Puerto Rico House and Senate are holding a joint hearing to consider a bill that would transition the island to 100% renewables.

In Puerto Rico, there were clear arguments for renewables even before the storm. The grid was already unreliable, and blackouts were common. Importing fossil fuels to the island is expensive, and electricity cost twice as much as it does on the mainland. The island has both abundant sunshine and wind. Maria made the case even stronger to switch to those power sources.

“It changed everything,” says Javier Rua-Jovet, who lives in San Juan and now works as director of public policy in Puerto Rico for SunRun, the solar power company, which entered the market there this year because of the demand for solar power and battery storage systems. “People were hurled back from the first world to the third world in terms of energy.”

Rua-Jovet’s own electricity was out for a relatively short two months (for some others, the blackout lasted nine months), but he spent around $1,700 on fuel for a generator during that time. Others suffered significantly more–some people died because they didn’t have the power to run a respirator or dialysis machine. It became clear to everyone, he says, that the energy paradigm needed to change. Long transmission lines crossing mountains, vulnerable in storms could be replaced by a more resilient system with energy distributed in many locations.

After Maria, SunRun, along with companies like Sonnen and Tesla, installed small solar microgrids–solar panels plus batteries to store the power–at sites like hospitals and fire stations. The systems worked, and have continued to work during more recent temporary blackouts. That helped bolster the political case for more microgrids, which the new bill supports as part of the shift away from fossil fuels. It’s also designed to support “prosumers,” consumers who can install rooftop solar systems and then sell excess power to the grid and their neighbors. Some disaster funding from the federal government may help homeowners buy panels. (A request from Puerto Rico to HUD currently asks for $100 million to go to solar power and storage.)

The storm “created broad consensus across the political spectrum,” says Rua-Jovet. “We have a pro-renewables governor. We have a pro-renewables Senate.” He’s optimistic that the bill will pass.


School District Soars Into The Future On Solar Energy

By: Bay Stephens

Members and businesses in the Big Sky community donated funds and time to install this array of photovoltaic panels at Ophir School. PHOTO BY BAY STEPHENS

BIG SKY – The spring of 2017 saw the installation of Big Sky School District’s 7.125 kW solar photovoltaic array on the south-facing roof of Ophir School. The system—an array of solar panels that looks down on the playground—along with a digital kiosk run by Bonneville Environmental Foundation displaying the energy data, exposes Big Sky youth to the possibilities of renewable energy.

Located near the gym in Lone Peak High School, the kiosk shows how much energy the solar array generates, allowing students to view output in real time and over time.

Also accessible online, the data shows that in the past 19 months, the array has generated more than 12,5000 kilowatt-hours of energy, enough to power an average home for 1 year or a TV for 12 years. The greenhouse gases avoided amount to about 17,700 pounds of carbon dioxide.

“We thought it was going to be cool idea,” Big Sky School District Superintendent Dustin Shipman said. “We wanted to be able to teach the kids about renewable energy options and what better way to do that when you have it right there in your own system.”

The community came together to bring the educational opportunity to fruition. Lisa Lillelund of Mango Networks coordinated funding for the $39,000 project, garnering a $29,000 Universal System Benefits Renewable Energy Grant from NorthWestern Energy. She said the project would have fallen flat without work by Energy 1, who procured and installed the solar array for a nominal fee, and two private donations from the Bulis family and Highline Partners.

“Alternative energy—especially solar—is a no-brainer in this nation,” Rob McRae of Highline Partners said. “I do think that in 10-15 years, there’s going to be tremendous growth in that industry.”

That growth is already evident. According to a September report by the Solar Energy Industries Association, in the second quarter of 2018 U.S. market installations of solar photovoltaic arrays increased by 9 percent, year-over-year, and in the first half of the year, 29 percent “of all new electricity generating capacity brought online in the U.S. came from solar PV.”

“I think people appreciate and love Big Sky because of its beauty, but the integrity of this place depends on being more environmentally friendly and having sustainable practices,” Ania Bulis said. “This [array] was an opportunity to send the right message to our children.”

Although the array doesn’t significantly offset the school’s energy costs, it sets a precedent in the community, beginning but not ending with education. Bulis thinks the next step in the right direction would be a long-term sustainability plan for Big Sky that all community members can get behind.

A next step for the school district could be more ability to function off the grid. “We would love to partner with any organization in order to expand our use of renewable energy,” Shipman said.



A Solar Cell That Does Double Duty For Renewable Energy

The HPEV cell’s extra back outlet allows the current to be split into two, so that one part of the current contributes to solar fuels generation, and the rest can be extracted as electrical power. Credit: Berkeley Lab, JCAP

In the quest for abundant, renewable alternatives to fossil fuels, scientists have sought to harvest the sun’s energy through “water splitting,” an artificial photosynthesis technique that uses sunlight to generate hydrogen fuel from water. But water-splitting devices have yet to live up to their potential because there still isn’t a design for materials with the right mix of optical, electronic, and chemical properties needed for them to work efficiently.

Now researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the Joint Center for Artificial Photosynthesis (JCAP), a DOE Energy Innovation Hub, have come up with a new recipe for renewable fuels that could bypass the limitations in current materials: an artificial photosynthesis device called a “hybrid photoelectrochemical and voltaic (HPEV) cell” that turns sunlight and water into not just one, but two types of energy — hydrogen fuel and electricity. The paper describing this work was published on Oct. 29 in Nature Materials.

Finding a Way Out For Electrons

Most water-splitting devices are made of a stack of light-absorbing materials. Depending on its makeup, each layer absorbs different parts or “wavelengths” of the solar spectrum, ranging from less-energetic wavelengths of infrared light to more-energetic wavelengths of visible or ultraviolet light.

When each layer absorbs light it builds an electrical voltage. These individual voltages combine into one voltage large enough to split water into oxygen and hydrogen fuel. But according to Gideon Segev, a postdoctoral researcher at JCAP in Berkeley Lab’s Chemical Sciences Division and the study’s lead author, the problem with this configuration is that even though silicon solar cells can generate electricity very close to their limit, their high-performance potential is compromised when they are part of a water-splitting device.

The current passing through the device is limited by other materials in the stack that don’t perform as well as silicon, and as a result, the system produces much less current than it could — and the less current it generates, the less solar fuel it can produce.

“It’s like always running a car in first gear,” said Segev. “This is energy that you could harvest, but because silicon isn’t acting at its maximum power point, most of the excited electrons in the silicon have nowhere to go, so they lose their energy before they are utilized to do useful work.”

Getting Out of First Gear

So Segev and his co-authors — Jeffrey W. Beeman, a JCAP researcher in Berkeley Lab’s Chemical Sciences Division, and former Berkeley Lab and JCAP researchers Jeffery Greenblatt, who now heads the Bay Area-based technology consultancy Emerging Futures LLC, and Ian Sharp, now a professor of experimental semiconductor physics at the Technical University of Munich in Germany — proposed a surprisingly simple solution to a complex problem.

“We thought, ‘What if we just let the electrons out?'” said Segev.

In water-splitting devices, the front surface is usually dedicated to solar fuels production, and the back surface serves as an electrical outlet. To work around the conventional system’s limitations, they added an additional electrical contact to the silicon component’s back surface, resulting in an HPEV device with two contacts in the back instead of just one. The extra back outlet would allow the current to be split into two, so that one part of the current contributes to solar fuels generation, and the rest can be extracted as electrical power.

When What You See is What You Get

After running a simulation to predict whether the HPEC would function as designed, they made a prototype to test their theory. “And to our surprise, it worked!” Segev said. “In science, you’re never really sure if everything’s going to work even if your computer simulations say they will. But that’s also what makes it fun. It was great to see our experiments validate our simulations’ predictions.”

According to their calculations, a conventional solar hydrogen generator based on a combination of silicon and bismuth vanadate, a material that is widely studied for solar water splitting, would generate hydrogen at a solar to hydrogen efficiency of 6.8 percent. In other words, out of all of the incident solar energy striking the surface of a cell, 6.8 percent will be stored in the form of hydrogen fuel, and all the rest is lost.

In contrast, the HPEV cells harvest leftover electrons that do not contribute to fuel generation. These residual electrons are instead used to generate electrical power, resulting in a dramatic increase in the overall solar energy conversion efficiency, said Segev. For example, according to the same calculations, the same 6.8 percent of the solar energy can be stored as hydrogen fuel in an HPEV cell made of bismuth vanadate and silicon, and another 13.4 percent of the solar energy can be converted to electricity. This enables a combined efficiency of 20.2 percent, three times better than conventional solar hydrogen cells.

The researchers plan to continue their collaboration so they can look into using the HPEV concept for other applications such as reducing carbon dioxide emissions. “This was truly a group effort where people with a lot of experience were able to contribute,” added Segev. “After a year and a half of working together on a pretty tedious process, it was great to see our experiments finally come together.”


Industry to Open a New Front in Rooftop Energy Revolution

Clean Peak Energy’s Phil Graham, JBS procurement manager Paul Rohl and Primo’s Gavan Scaroni inspect the installation at Wacol. Attila Csaszar

By: Angela Macdonald-Smith

When Primo Smallgoods decided to install the country’s largest rooftop solar array, it wasn’t thinking of anarchy, nor of saving the world or going off-grid. It was just rational economics.

“This made sense up in Queensland: there’s a lot of sunshine and the roof is very large. It all stacked up to make a good business case,” says chief operating officer Bruce Sabatta, who is always on the hunt for efficiencies in energy supply for the freezers and refrigeration systems of the southern hemisphere’s largest ham and bacon producer.

“This is finding a way to try to future-proof our efficiency as well as pick up on the sustainability piece.”

Covering about 25,000 square metres of rooftop at Primo’s plant in Wacol, southern Brisbane, the 3.2 megawatt installation will replace almost 20 per cent of the site’s demand for power from the grid. The industrial market for rooftop solar is expected to triple next year as more businesses turn the roofs of their factories and warehouses into power plants.

By 2050, solar systems installed “behind-the-meter” – generating power on-site that is not supplied from the centralised grid – are expected by Bloomberg New Energy Finance to make the consumer the most influential electricity generator in the country. Solar will by then meet by far the majority of demand during peak daylight hours, with batteries playing an increasing part after hours.

A sign of what’s to come was reported by the Australian Energy Market Operator last week, when it noted a new record for minimum grid demand in South Australia. Rooftop solar was generating so much electricity during the middle of the day on Sunday, October 21, that it reduced demand for power from the grid to its lowest ever.

The result is that swings in demand required from the grid are becoming bigger and more common, creating challenges for AEMO’s forecasters as they try to calculate the next day’s grid demand and ensure sufficient flexible generation can be brought online.

Australia’s rooftop solar boom has until now been led by households enthusiastically snapping up subsidies and feed-in tariffs and harnessing the “free” power of the sun to power their devices and air conditioners. But the economics are increasingly making sense also for businesses, which will fuel an acceleration of rooftop solar from the already frenetic pace of installation put by Audrey Zibelman, chief executive of AEMO, at a world-leading rate of six-and-a-half panels a minute.

“We expect a massive boom in larger rooftop systems,” says Kobad Bhavnagri at BNEF, which sees Australia becoming the most decentralised energy system in the world after Brazil.

Rooftop solar caused record low demand for power from the grid on October 21, 2018. AEMO

“In time, when that comes to its fullness, it will dwarf what we’ve seen on residential rooftops.”

BNEF expects that by mid-century rooftop solar and behind-the-meter batteries will make up 44 per cent of Australia’s total power capacity, representing a massive shift of value away from centralised power stations.

For commercial and industrial users of power, who pay much lower prices than households and who tend to make more financially rational decisions, it has taken longer for the economics of solar to develop.

“But we see now that it does stack up for small and medium enterprises … and in the early 2020s we think that will pretty much cover all types of large energy users,” Mr Bhavnagri said.

Philip Graham, one of the founders of Clean Peak Energy, which stitched together Primo’s solar supply, is expecting the commercial and industrial market for rooftop solar to reach 300 MW next year from this year’s 100 MW-plus, already up six-fold from two years ago.

The trend is part of what Energy Security Board chief Kerry Schott described this month as a state of “anarchy” in energy supply, created by a combination of cheap renewables, transmission constraints, “dumb” distribution grids and policy failures on emissions.

But Mr Graham, Citigroup’s former head of utilities investment banking in Asia, says the sheer scale of the rooftops and of the energy consumption of industrial customers means the efficiency of such systems beats household rooftop hands down. He compares the horde of 5 kilowatt residential rooftop systems with their costly up-front subsidies and their impact on grid stability unfavourably with a 1 MW installation for a large industrial consumer.

For those with suitable buildings, rooftop systems can also be more economic than solar power purchase agreements, or solar PPAs, where an industrial customer typically contracts for power from a utility-scale solar farm.

Primo’s 3.2 MW solar system covers about 75 per cent of the site’s roof, or about 25,000 square metres. Attila Csaszar

Mr Graham said typical prices of $50-$70 a megawatt-hour for a solar PPA rise north of $100/MWh for a delivered price, which includes transmission and distribution costs, the retail margin and “load shaping”, the cost of hedging to deliver firm supply.

“By building a large system on a rooftop we can be inside of that on a cents per kilowatt basis behind-the-meter because we don’t have to pay all the extra charges,” he said.

“So from an economic perspective it’s far more efficient in pricing to be looking at large rooftop solutions because you don’t have to go through the whole cost structures to deliver paddock-based power stations into the site.”

At Wacol, Clean Peak paid for and owns the rooftop system with its panels supplied by Todae Solar, and sells power to Prime under a fixed rate, 10-year deal. There is no reliance on feed-in tariffs as all the energy is used on site, while Clean Peak takes the risk on the Renewable Energy Certificates it generates.

“The reason it’s working for us is we are constantly running that facility, we don’t have a lot of downtime,” said Mr Sabatta, noting the deal also helps contribute to the international sustainability targets of Primo parent company JBS.

“We start seeing savings from the first year and that continues throughout the usable life of the panels. We are hoping for 30 years out of these at least.”

While Primo has no need for batteries at Wacol, Mr Graham sees storage as critical for Clean Peak’s future, to reduce the price risk on its supply contracts with corporate customers.