A review of energy harvesting technologies for railway systems: principles, applications and challenges

• Systematic review links energy conversion mechanisms with railway deployment. • Vibration harvesters are grouped as onboard, track mounted, and bridge mounted. • Wind, solar, and thermal routes are assessed with vibration energy harvesting. • Electromagnetic and piezoelectric routes show stronger engineering maturity. • Main gaps include variable excitation efficiency, durability, and life cycle cost. Rail transport is becoming more central to integrated mobility systems, yet distributed railway health monitoring still faces a critical power bottleneck. Reliance on external energy supply constrains long-term maintenance-free operation. Harvesting secondary energy generated during train operation, such as vibration, airflow, solar radiation, and heat, offers an alternative. A systematic review is presented to synthesise railway energy harvesting technologies from mechanism to application. Primary conversion routes include piezoelectric, electromagnetic, and triboelectric mechanisms. Auxiliary conversion mechanisms include photovoltaic, thermoelectric, and electrostatic technologies. Vibration harvesters are reclassified by installation domain as onboard, track-mounted, and bridge-mounted, enabling comparative analysis of structural design, output characteristics, durability, and application suitability. Wind, solar, and thermal energy harvesting technologies are integrated to assess multi-source energy supply pathways for intelligent railway monitoring. Evidence indicates that electromagnetic and piezoelectric approaches provide the strongest engineering maturity. Major barriers remain in conversion efficiency under variable excitation, long-term material reliability, and life-cycle economic competitiveness. Future progress should focus on hybrid multi-source architectures, interdisciplinary co-design of materials, devices, and power management, and service condition validation. Experimental datasets for the reviewed devices are provided in Appendix A to support benchmarking across studies.