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This paper proposed a portable balloon-integrated photovoltaic system (BIPVS) deployed at low altitude. The inflatable and deflatable design enhances the proposed system flexibility and mobility, enabling it have a wider range of application scenarios. Case studies were conducted based on cities' data of Vasteras, Vancouver, New York, Shanghai and Hong Kong to evaluate 10,000 BIPVS's annual power generation potential. Mid-to-high latitudes are not suitable for photovoltaic power generation in winter due to snow and ice coverage. Excluding the unsuitable winter months, simulation results show that the average monthly power generation of the BIPVSs amounts to 3.921 GWh, 4.238 GWh, 4.275 GWh, 3.337 GWh, and 3.379 GWh, respectively, during the effective working months within a year, which shows the superior performance of mid-to-high latitudes over their low latitudes. Over the life cycle, the BIPVSs exhibit a cumulative power generation capacity, amounting to 479.492 GWh, 592.18 GWh, 672.105 GWh, 641.155 GWh, and 708.334 GWh, respectively, and their total profits are 79.614 million USD, 37.007 million USD, 75.146 million USD, 12.946 million USD, 107.369 million USD, accompanied by the return on investment of 218.6 %, 101.6 %, 206.3 %, 35.5 %, 294.8 %, respectively. These findings illustrate the significant energy and economic advantages and potential of BIPVS.

Vibration energy harvesting technology is characterized by wide distribution, is pollution-free and independent of weather and climate, and is suitable for powering low-power sensors to ensure efficient and safe operation in freight railroads. This paper proposed an electromagnetic vibration energy harvester based on a series coupling input mechanism for the self-powered sensors in freight railroads. The design utilizes only one rack for vibration energy input to minimize the moment acting on the vibration source during the working process. Two pinions meshed with the rack convert the up and down vibrations into a two-way rotation. The one-way bearings and another pair of gears convert the opposite rotations of two parallel shafts into one-way rotation of the generator shaft, generating electricity. Supercapacitors and rectifier voltage regulator modules are utilized to store electrical energy efficiently. A peak power of 10.219 W and maximum mechanical efficiency of 64.31% is obtained in the experiment equipped with a flywheel under the 8 mm-4 Hz sinusoidal vibration excitation. The experimental results showed that the flywheel can enable the proposed harvester to achieve better power generation performance when the amplitude and frequency are relatively high. 

The vibrational energy, often considered a negative factor, is abundant in everyday life. Especially in railway systems, the negatively impacted track vibrations resulting from moving trains can be captured to provide a practical power supply solution for wireless sensor networks. This paper proposed a variable damping vibration energy harvester with a half-wave flywheel for a freight train-based railway. A double-sided rack as the input member converts the track vibration into the opposite rotation of the two pinions, which are then transmitted to the two parallel shafts respectively. According to the work characteristics of the one-way bearing, the upper and lower vibrations can be collected separately and output a one-way rotation to the generator module. The proposed harvester with a half-wave flywheel features a larger damping force for vibration reduction during the downward track vibration and a smaller damping force conducive to returning the track's original state during the upward track vibration. The experimental results achieve a maximum output power of 10.247 W and a maximum mechanical efficiency of 74.49%. Both simulations and experiments have verified that the proposed system with a half-wave flywheel can increase the damping force in the vibration reduction process and reduce the damping force in the reset process, which is characteristic of improving its power generation performance with a good vibration reduction effect. The VEH with the half-wave flywheel achieved an average power of 5.321 W at the train speed of 90 km/h under random vibration testing, which verifies the feasibility of self-powered wireless sensor networks in railway environments. 

To ensure the efficient and safe operation of train transportation systems, the track vibration resulting from train movement can be utilized to power the sensors for intelligent applications. This paper presents a vibration energy harvesting system based on track energy-recycling technology for heavy-duty freight railroads. The energy-recycling system includes a vibration conversion module, a generator module and a power storage module. The irregular vertical vibrations produced by contact between the wheel and railroad are considered. The vibration conversion module converts the reciprocating vertical displacement into a one-way rotation through a scissor linkage and slider mechanism. A three-phase generator is coupled with an energy conversion module shaft and generates a three-phase direct current. Then, after rectification and filtering, the electricity is stored in the supercapacitors. Theoretical analysis, dynamic model analysis and mechanical simulation verify the dynamic response of the system under input excitation. Furthermore, mechanical testing and sensing (MTS) machine tests yield a 73.38% maximum mechanical efficiency with a 7.44 W peak power. Moreover, the charging tests of the proposed system with a supercapacitor indicate that the proposed system is suitable for self-powered sensors in railroads.