Davidson, J., Collins, M., and Behrens, S. (2009) Thermal energy harvesting between the air/water interface for powering wireless sensor nodes. Proceedings of SPIE, 7288. - .

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Abstract

Seventy percent of the Earth's surface is covered by water and all living things are dependent upon this resource. As such there are many applications for monitoring environmental data in and around aquatic environments. Wireless sensor networks are poised to revolutionise this process as the reduction in size and power consumption of electronics are opening up many new possibilities for these networks. Aquatic sensor nodes are usually battery powered, so as sensor networks increase in number and size, replacement of depleted batteries becomes time consuming, wasteful and in some cases unfeasible. Additionally, a battery that is large enough to last the life of a sensor node would dominate the overall size of the node, and thus would not be very attractive or practical. As a result, there is a clear need to explore novel alternatives to power sensor nodes/networks, as existing battery technology hinders the widespread deployment of these networks. By harvesting energy from their local environment, sensor networks can achieve much greater run-times, years not months, with potentially lower cost and weight. A potential renewable energy source in aquatic environments exists via the temperature gradient present between the water layer and ambient air. A body of water will be either a few degrees warmer or colder than the air directly above it dependant on its latitude, time of year and time of day. By incorporating a thermal energy harvesting device into the sensor node deployment which promotes the flow of heat energy across the thermal gradient, a portion of the energy flow can be converted into useable power for the sensor node. To further increase this temperature difference during the day the top section can be heated to temperatures above the ambient air temperature by absorbing the incoming sunlight. As an initial exploration into the potential of this novel power source we have developed a model of the process. By inputting environmental data, the model calculates the power which can be extracted by a thermal energy harvesting device. Initial outputs show a possibility of up to 10W/m2 of power available from measured sites assuming a thermal energy harvester operating with Carnot efficiency.

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