Taking inspiration from the natural design of leaves, chemical engineers at Imperial College London have made solar panels that can cool themselves down with water without using any energy, which boosts their performance.
The solar leaves, reported in the journal Nature Communications, keep cool by about 26 °C when exposed to direct sunlight on a clear day. This leads to a 13.6 percent increase in the efficiency with which they convert solar energy to electricity.
What’s more, the devices also capture clean water vapor to produce liters of freshwater every day. Per the team’s projections, 8.5 terawatts of installed solar panels with a solar leaf structure could produce over 40 billion cubic meters of freshwater each year, “significantly relieving the stress of global water scarcity,” write the researchers.
Solar panels usually only convert about 10 to 25 percent of sunlight into electricity. The rest of the energy gets converted to waste heat, which brings down their performance. They are typically cooled using air or water, but this requires complicated piping and pumps.
Chemical engineer Gan Huang and colleagues made a passive, energy-free cooling system by borrowing a page from plants. Plants send water from the soil up to their leaves through various tubular structures. Natural capillary forces and osmotic pressure drive the flow of water. Veins in the leaves then distribute water through the structure so it can evaporate on the leaf surface. This whole process of water movement through a plant and its evaporation from leaves is called transpiration.
The researchers made a similar transpiration system for solar cells. They pasted bundles of bamboo fibers on a steel wire mesh, and coat it with a water-absorbing hydrogel. They attached this 1mm-thick layer to the back of a 10 cm x 10 cm solar cell, and put the ends of the bamboo fibers into a water tank.
The bamboo fiber bundles act as veins, siphoning water up from the tank to the hydrogel, which soak it up and spread it all over the underside of the solar cells. There, the water evaporates, drawing heat away from the solar cell. The researchers collect the water vapors using a collection chamber they place under the transpiration layer.
Under full sun, the solar leaf device had 14.5 percent efficiency, while a regular solar cell had an efficiency of 13.2 percent. The device produced over a liter of water every hour.
Because the transpiration layer is made from widely available, affordable, and environmentally-friendly materials, it should relatively easy to mass manufacture and to compete with established technologies, the researchers write.
“Implementing this innovative leaf-like design could help expedite the global energy transition, while addressing two pressing global challenges: the need for increased energy and freshwater,” said paper co-author and chemical engineering professor Christos Markides in a press release.
Source: Huang, G., Xu, J. & Markides, C.N. High-efficiency bio-inspired hybrid multi-generation photovoltaic leaf. Nat Commun, 2023.
Image: Conceptual structure of PV-leaf. ©Dr Gan Huang.