Technologies for high-entropy energy harvesting and utilization along transport infrastructures

The method of harvesting high-entropy energy from the transportation environment and converting it into electrical energy can provide a guarantee for the regular operation of low-power devices in the era of the Internet of Things. There have been many studies on high-entropy energy harvesting technologies in transportation, represented by thermal and mechanical energy harvesting technologies. Among them, thermal energy harvesting technology reduces the urban heat island effect while recycling energy, but its power generation efficiency is low. In contrast, mechanical energy harvesting technology has received more attention because of its wider application range and better energy recovery effect. Mechanical energy harvesting devices are mainly categorized into electromagnetic generators, piezoelectric generators, and triboelectric nanogenerators. The electromagnetic generator has a high output current but a complex structure and a large size. The piezoelectric generator has a simple structure but low output power and current. The triboelectric nanogenerator also has low output power and current, but its output voltage is high. This study introduces the existing energy harvesting technologies by summarizing and sorting out the current state of researches, focusing on the principles, characteristics, and shortcomings of these technologies, discussing the challenges faced by each technology, and making suggestions for future research directions.