Experimental Validation of Energy Harvesting-System Availability Improvement Through Battery Heating

Abstract

Operation of wireless sensor nodes or battery powered embedded systems in cold and harsh environments requires careful battery selection and management. In this paper we first provide a general model of an energy harvesting sensor system and the respective energy flows. We then present a Maximum Power Point Tracking solar harvesting system according to that model. The system is coupled with rechargeable Li-ion batteries and equipped with a battery heating mechanism. The significant signals of that system are monitored to have a deeper insight into the energy distribution. Real-world experiments demonstrate benefits of battery heating during high irradiation periods at temperatures below safe charging conditions. The presented case study for a cold winter day shows that the additional energy which can be stored thanks to battery heating would more than double the autonomy of the sensor system.

Existing System

Power management in energy harvesting sensor networks.

Proposed System

In this paper we focus on energy harvesting and on ensuring that energy could be stored in the batteries through battery heating. We present a general model of an energy harvesting sensor system and a particular implementation that we built and tested in outdoor environment. The significant elements and the internal signals of the system are monitored, allowing us to follow all phenomena related to solar harvesting and put them into relation with the environment (i.e., weather condition changes regarding clouds, fog, sun, temperature, etc.). Our case study shows that heating the battery in sunny and low-temperature (below 0_C) weather conditions allows storing otherwise lost energy. The example of a sunny and cold winter day demonstrates that a significant amount of energy can be saved for possible later exploitation, if a (small) amount of energy is diverted for heating directly from the solar panel. The contribution of this paper is twofold: We show the benefits of battery heating for energy harvesting sensor systems with Li-ion batteries under cold and sunny conditions. To the best of authors knowledge, this is the first paper that provides an analysis of battery heating for energy harvesting embedded sensor systems; We verify our assumptions in an experimental setup with a real-world energy harvesting embedded sensor system.

Architecture

Energy flow in an energy harvesting sensor system

Block scheme of the developed harvesting system