A Study Of Solar Energy Sensor Node For Sustainable Wireless Sensor Networks

The rapid advancement in processor, sensor, and radio technology enable the development of wireless sensor networks of small, inexpensive nodes that are capable of sensing, computation, and communication. Such technology has been widely used in environment monitoring, military surveillance, scientific research, health care and so on. For the applications where the systems are proposed to operate for long durations, energy has become a severe bottleneck. The load varies over a huge range microwatts in standby and milliwatts when active, thus a sensor node can only sustain a few days in 100% duty cycle in traditional battery-powered sensors. In order to achieve sustainability, environmental energy harvesting has been demonstrated to be a very promising approach.Certain considerations in utilizing an environmental energy source are fundamentally different from that in utilizing battery, because, rather than a limit on the maximum energy, it has a limit on the rate at which energy can be utilized. In addition, the energy harvested from solar typically varies with time in a nondeterministic and uncontrollable manner. The key issue attracted most attention is making full use of environmental energy while maintaining the sustainability of the wireless sensor networks. Different from previous works, we believe that the consumption of energy should balance the generation in real time, and the primary requirement for an efficient and long-term solar powered sensor system is to adapt to changing environment condition and resources, and to gather as much valuable data as possible.In this work, we design and evaluate a high efficient and robust solar powered system called SolarMote. And we further analyze the energy harvesting theory, and propose a metric--energy neutral operation, which can be expected in situations where energy consumed by the system is equal to or less than the energy harvested from the environment. We then propose power management theory to investigate the relationship between energy generation and consumption. In this system, a practical energy prediction method and a dynamic duty cycle adaptation are presented in order to achieve the energy neutral operation. We deployed SolarMote in the forest for nearly two month to evaluate the stability and sustainability, which eventually results corroborate our design.