Wave energy advances with the electrostatic generator.

One of the keys to obtaining clean marine energy, at least a small part, may lie in static electricity. A research team in Portugal has now successfully used it to drive a small generator in the navigation buoy. Many sensors and lights are usually arranged in these buoys to collect data and help sailors. Although the scale of this project is very small so far, the researchers said that it is an important proof of a technical concept, which can supplement the existing attempts to use wave energy and other naturally occurring sports.

Ocean is an attractive target for renewable energy power generation. Only waves can generate 32,000 TWh of natural energy every year. For reference, the world uses about 23,000 TWh of energy every year. In addition, there are ocean currents, tides and heat energy available in the ocean. Although scientists have studied it for decades, it is still difficult to control the motion of the ocean because the motion pattern of waves is unpredictable. Seawater corrodes metal power generation devices, and wave energy is dispersed in three-dimensional space (up and down, back and forth, left and right) at the same time.

To a certain extent, it is precisely because of these challenges that the power generation of several large-scale wave power generation projects just started lags behind expectations. Portuguese researchers turned to a smaller, more manageable project: powering navigation buoys, which usually include lights to guide ships and sensors to monitor ocean conditions. The research team turned to the so-called "Triboelectric Nanogenerators" (TENGs), which use static electricity to convert motion into current, and the principle is the same as rubbing balloons on sweaters to generate charge. The core of each vine has two surfaces, only a few square centimeters in area, which can be easily positively or negatively charged. On these two stacked surfaces, the researchers placed 10 stainless steel balls with a diameter of about 12 mm, which can move freely. When the container is tilted, the ball will roll and rub two surfaces. This forms an electrostatic charge, which can be converted into electrical energy to power the battery.

Katia Rodriguez, a doctoral student in nanotechnology at the University of Porto in Portugal, said: "We have developed these new devices, which can convert rhythm and mechanical energy into electrical energy." Last week, she gave a speech about her team's wave energy buoy at an online meeting organized by the American Institute of Physics. "The cost of these devices is very low. They achieved high power density and high efficiency, "Rodriguez said, adding that Teng performed well, even though the waves were small and few.

ENGs can generate energy from any form of motion, but Rodriguez and her collaborators focus on testing various TENGs prototypes to optimize their adaptation to specific conditions of wave motion. In their recent test, she and her colleagues wanted to know how to make the electricity generated consistent: put all the balls in a round shallow bowl structure, or create a separate "lane" for each ball to move on the floor.

In the hydraulic laboratory of the University of Porto, the research team tested the design of TENGs embedded in an eighth-scale replica of the ocean buoy. They put the model in a wave pool and simulated the five most common wave modes in the port near Figuera Davos.

TENGs was invented by a researcher at Georgia Institute of Technology in 20 12. Rodriguez said that this new study marks the first time they have been tested under such real wave conditions. The final project proves that the maximum output power generated by the design of swimming lane TENGs is 230 microwatts, which is enough to supply power for small equipment such as medical implants. Compared with the bowl design, it can also convert energy more consistently under different wave conditions. Rodriguez said that by adding multiple TENGs or nanoparticles to the surface below the metal ball, the power generation capacity of the metal ball can be improved, thus increasing the ability of the material to accumulate charges.

Andrew Hamilton, director of the engineering department of the Monterey Bay Oceanographic Research Institute in California, who was not involved in the new work, said that TENGs may provide a solution to a key problem that hinders other marine energy technologies. The ocean is a high-intensity and low-speed system: it contains a lot of energy, but this energy is widely distributed. The energy required by traditional rotary generators to generate electricity often exceeds the energy provided by a small ocean, and other attempts to develop wave energy buoys are also flawed. Monterey Bay's own buoy project uses the motion difference between the water surface and the platform suspended below tens to hundreds of meters to generate electricity. But to work in deep places, you need a long cable that can withstand the damage of waves and underwater currents. In 20 17, a navigation buoy in India used an oscillating water column system to provide power for itself: waves alternately filled and emptied a partially submerged cabin, accelerated air in and out of the water column, and the fast-flowing air drove the turbine to generate electricity. But this method will produce potentially problematic noise, and it only uses the vertical motion of waves.

TENGs' small scale helps it avoid these two defects. Rodriguez said that compactness is one of its advantages, which makes it easy for researchers to combine TENGs with other power generation methods, such as solar panels or different kinds of wave energy collectors. Based on the success of their wave pool experiment, the researchers plan to modify their TENGs prototype and install it in a full-scale buoy. Hamilton pointed out that testing on the high seas may encounter challenges that cannot be simulated in a wave pool. He said: "Anything you design that can be used in the ocean all year round must be designed for a storm that statistically occurs once every 100 years." He explained that this extreme weather resistance usually makes the equipment bigger, harder to operate and less durable over time, because the increased surface area provides more opportunities for wear and tear.

Rodriguez is not discouraged. She said that she was not only studying the performance of Teng in the ocean, but also studying the performance under other "harsh conditions", including that they were put into underground wells and sewn into insoles. These wide applications are the reason why she hopes to see TENGs "everywhere" in the future.