One of the major challenges in WSN are the energy limitations. What are the most recent advances in energy harvesting solutions for Wireless Sensor Networks (WSN)?
I think the most available energy harvesting source for wireless sensor network is the solar energy with solar cells as conversion devices in addition to battery storage. Other sources are available to less extent such as the vibration sensors and thermometric converters. There is also the piezoelectric sensors.
For more information please see the link:Chapter Research in Energy Harvesting Wireless Sensor Networks and t...
The MAC protocols and other techniques at network layers have also been developed in order to optimize energy. One very basic protocol is sleep MAC where the device is scheduled to sleep (Switch off) for a certain period to avoid power consumption. This sleep scheduling is timed using machine learning algorithms. Many such advancements have been made in other protocols as well.