TWH – Solar power offers one way out of the climate crisis. Serious critics of solar power, however, point out some of its obvious limitations. It only generates power when the sun is shining, and currently, solar power’s capacity for storage is limited. Researchers have recently made several advances that challenge those criticisms.
Field of regular solar panels in Somerset, England – Image credit: by Lewis Clarke – CC BY-SA 2.0
Scientists at the University of California, Davis have developed a “reverse solar cell” that can generate energy at night. Swedish scientists have developed a way to store solar energy for up to 18 years, and an engineering student has built solar panels from plant waste. All three had passed the proof of concept stage, but have yet to become economically efficient. Scientists need to do more work before consumers can use these innovations.
Reverse solar cells
ACS Photonics reported that these “reverse solar cells” work like simplified heat engines. Regular solar cells are cool compared to the sun. They absorb solar heat. That heat is then transformed into energy.
UC Davis News described the development of TR cells. Jeremy Munday, a University of California, Davis professor said, “We were thinking, what if we took one of these devices and put it in a warm area and pointed it at the sky.”
Munday continued, “A regular solar cell generates power by absorbing sunlight, which causes a voltage to appear across the device and for current to flow. In these new devices, light is instead emitted and the current and voltage go in the opposite direction, but you still generate power … You have to use different materials, but the physics is the same.”
Designers could create a cell with a special material on its underside that transfers warmth from the earth to the cell. The cell in direct contact with the earth could then draw continuous warmth from the earth. Pointed upwards at the night sky, the heat transfer would go from the earth outward toward deep space.
The technical term for this type of reverse solar cell is a “thermoradiative” cell or TR cell.
These types of TR cells could also capture heat from a hot engine or machine in a factory. Currently, that heat is wasted. A TR cell could capture that heat and transform it into energy. When waste becomes useful, the efficiency of the process would increase. Profits would increase. As such, it would encourage corporate uptake.
A TR cell employs passive cooling. This type of cooling has been employed for centuries, like simply opening a window to cool off. Another instance of passive cooling involves color. Painting a structure white causes that structure to reflect the sun’s heat outwards.
Passive cooling also occurs in nature, though the effects of climate change have had an impact on the process. In the past, the white snow and ice cover in the Arctic reflected the sun’s heat outward. This passive cooling helped to maintain the cold temperatures at the poles. Increased global temperatures, however, have caused the white snow and ice cover in the Arctic to begin melting. Without that cover reflecting outwards, the sun’s heat is no longer reflected outwards into space. The Arctic becomes warmer in a reflexive feedback loop.
In a news statement, the American Academy for the Advancement of Science (AAAS) reported that a group from Stanford was also working on TR cells.
Earlier attempts had failed to generate enough energy efficiently. These Stanford researchers turned their TR cells to face deep space. This time, they generated a measurable amount of electricity. While measurable, the amount was much less than the theoretical limits. It also lacked efficiency.
In 2020, UC Davis News reported about this technique. Munday said one of these TR cells could generate as much as 50 watts of power per square meter at night. A regular solar cell would generate about 200 watts during the day. The UC Davis team is now working to improve their efficiency.
Solar storage for up to 18 years
In 2017, Swedish scientists developed an energy system that captures and stores energy for up to 18 years. They called this process the Molecular Solar Thermal Energy Storage Systems (MOST).
Professor Kasper Moth-Poulsen, at Chalmers University of Technology in Sweden, described it as a radical new way to generate electricity from solar power. The scientists designed a molecule, made of carbon, hydrogen, and nitrogen. That molecule will shift its shape in the presence of sunlight. It becomes an “energy-rich isomer.”
An isomer is defined as “one of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties.”
That isomer stores energy from sunlight. In order to harvest that energy for use, scientists have developed a catalyst that will cause the isomer to release its energy as heat and to return to its original shape.
In 2022, Swedish scientists sent some isomers to Jiao Tong University in China. Chinese scientists then activated the catalyst. They used a generator to transform that heat into electricity. Those scientists could then use the stored Swedish sunlight as a source of electricity in China, thousands of miles away.
Solar panels that work without direct light
Carvey Ehren Maigu, 29, is a Filipino engineering student who has developed a solar panel from plant waste that utilizes the sun’s ultraviolet rays. Even on overcast days, ultraviolet rays reach the earth.
Maigue gathered the plant waste and “crushed, juiced, and filtered [the waste] to extract the luminescent particles.” Next, he suspended the particles in resin and then molded the resin to cover a window. Maigue placed photovoltaic cells along the edges of the resin. The photovoltaic cells could then generate enough electricity to charge two phones each day.
The use of plant waste would provide a kind of poetic symmetry. Typhoons and hurricanes leave lots of plant waste in their wake which could then be harvested to build this type of solar panel.
In 2020, Maigue won the James Dyson Foundation Sustainability Award.
While these impressive breakthroughs are only in their early development phase, they certainly offer hope for the future. Depending on the political will in the U.S., as well as other major economies, whether these new breakthroughs move beyond their early development phase is yet to be determined.
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