Autonomous underwater vehicles and sensors powered by ocean thermal energy

This paper will describe a compact energy generation and storage system to harvest temperature differentials in the ocean. This is a unique power source underwater in the absence of solar and wave energy. The current state-of-the-art autonomous underwater vehicles and sensors are mostly powered by primary battery, and therefore have limited capacity and lifetime. Harvesting the ocean thermal energy associated with vertical temperature differentials between the warm surface and cold deep water has the potential to power these autonomous underwater vehicles and sensors indefinitely. Results from the development, deployment and recovery of a prototype thermal recharging underwater float (known as SOLO-TREC) in the ocean will be presented. With eight hours energy harvesting and sampling interval, SOLO-TREC has made more than a thousand dives between the ocean surface and 500 meters water depth over a period of 1.5 years. Recent progress to commercialize this thermal recharging technology in support of several climate and oceanographic initiatives will be presented. Future applications of this thermal energy harvesting technology to power autonomous underwater vehicles such as gliders and propeller-driven AUVs will also be discussed.

I. Introduction

The interior ocean has been mainly observed using instruments lowered from research ships or mooring platforms. Ocean exploration by ships dated back to the Challenger expedition of 1872–1876 (1). Today, the U.S. oceanographic community has a dozen ships that are shared and managed by University-National Oceanographic Laboratory System (UNOLS), an organization of 62 academic institutions and National Laboratories involved in oceanographic research. Contrast to moving ships, a mooring platform is stationary at a fixed location, and can attach sensors along the wire connected to the anchor on the seafloor. The best example is the Tropical Atmosphere/Ocean (TAO) array with more than 70 moorings in the equatorial Pacific to monitor and enable the skillful forecast of El Nino (2). The relatively high cost of these observation platforms has limited their numbers and, consequently, the spatial and temporal density at which the ocean has been observed.