Engineered wood provides solar power even after the sun goes down

While sustainable solar energy can potentially meet our global power needs, it has one major flaw. When sunlight disappears, solar panels stop generating electricity. The problem is that while they do an excellent job of converting light into power, they are not so good at storing the energy they collect.

One solution is to use materials known to capture heat and release it later, such as phase change materials (PCMs). However, these can leak when they melt, struggle to conduct heat quickly, and catch fire easily. So researchers from China decided on a different approach, turning wood into a multifunctional solar-thermal energy storage material, as they detail in a paper published in Advanced Energy Materials.

Reengineering balsa wood

The team redesigned the internal structure of balsa wood at multiple scales, from nano to micro, to create a material that absorbs sunlight and stores it as heat for later use. It can also generate electricity when that stored heat is released through a thermoelectric device.

They first removed the wood's natural lignin, which acts as a glue holding the fibers together. This left behind a porous structure of tiny open channels. Then they coated the inside of these channels with ultrathin sheets of black phosphorene, which absorbs sunlight across multiple wavelengths and converts it into heat. However, phosphorene degrades quickly in the air, so the scientists added a protective layer of tannic acid and iron ions.

The next step was to add silver nanoparticles to help the wood capture sunlight. Finally, they added a water-repellent layer so the material stays dry and resists rot in all weather.

Once the balsa wood scaffold was ready, the researchers filled it with a heat-storing wax called stearic acid. This bio-based phase change material melts and stores energy when heated and solidifies and releases that energy when cooled.

One reason this wood is so thermally efficient is that heat travels along the grain rather than across the surface. This means it moves faster toward an external generator to be turned into power.

Impressive performance

To prove that their innovation works, the team ran several tests. In a solar simulator, it achieved a photothermal efficiency of 91.27%, meaning almost all the light hitting it became usable heat. The material also stored 175 kilojoules of energy per kilogram. When connected to a thermoelectric generator, the modified balsa wood produced up to 0.65 volts.

Beyond energy, it performed well against common hazards that wood structures face outdoors, such as fire, bacteria, and fungi. "The hybrid coating also greatly improves fire safety by reducing the HRR and THR by 27.4% and 31.2%, respectively, and it works well against E. coli and S. aureus," commented the study authors in their paper.

By addressing some of these issues, the team is moving closer to a practical solution for harnessing solar power even after sunset. "This work presents a scalable and environmentally friendly wood-based platform for advanced solar thermal energy harvesting."

Written for you by our author Paul Arnold, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.