Wave Powered Buoys as a Persistent Sensor Platform for High Latitude Environmental Monitoring

Marine sensing platforms for oceanography, atmospheric and general maritime monitoring are traditionally powered by photo voltaic solar cells. In the low flux regions of high latitudes, solar power performance can be poor, and seasonal limitations on power production can be extreme. This paper introduces an alternative power source, viz. using wave energy harvesting, to produce significantly higher power, more reliably and more consistently than the alternatives. Wave energy harvesting has a long and somewhat checkered history. Many different techniques have been tried and tested, with successes and failures, but the industry is now at a stage where a few key alternatives are approaching commercialization. There remain many challenges for the large grid connected devices, mostly surrounding economics and reliability of large and complex marine structures. In addition to utility scale devices, OPT's PowerBuoy technology has been developed with support from the US Navy as a stand-alone “autonomous” device. For our purposes here, autonomous is defined as a device which can be deployed and then operated without connection to shore and without a requirement for planned manual intervention, for the purpose of producing power from waves for point of use applications. Autonomous PowerBuoys range in size from 10W through to 350W and use a technology which can be extended further to larger powers. The device is designed to exploit the relative difference in motions between two hulls. Each hull is tuned to respond oppositely, one dynamically with the wave and one highly damped hull which resists motions from the wave forcing. By careful design, significant electrical power can be obtained from this resultant mechanical energy, across a wide range of wave lengths and periods; although the control systems involved can become very complex if maximum power extraction is to be achieved. This paper will outline the basics of the technology and control systems. It will discuss the challenges and outline how a flexible, efficient device has been designed. A discussion of the performance of one of the APB-350 (350W) devices during a recent redeployment for the US Navy in conjunction with Rutgers University will be presented. In this deployment, the PowerBuoy was configured with an HF RADAR system and, used in a bi-static configuration, was able to effectively double the range of the land based RADAR network offshore. Results and future developments will be shown. In the conclusions, the paper will introduce other typical applications and review the capabilities of the PowerBuoy as a flexible marine sensor platform for any latitude.