SOLO-TREC is the first unmanned underwater vehicle (UUV) that is completely powered by renewable energy, which is the temperature differences in the ocean. After five years of research, development and implementation, a group of scientists and engineers from JPL and Scripps Institution of Oceanography deployed SOLO-TREC southwest of the Hawaii Islands on November 30, 2009. Funding was provided initially by the JPL Research & Technology Development (R&TD) program during 2005-2007 and subsequently by the Office of Naval Research (ONR) during 2008-2010. Special Phase Change Materials (PCMs) on-board the SOLO-TREC expand about 13% when heated above 10 degree Celsius and then correspondingly contract when cooled below 10 degree Celsius. This expansion/contraction produces a high pressure oil that can be collected and periodically released to drive a hydraulic motor for electricity generation and battery recharging. Since its deployment, SOLO-TREC has been making 3~4 dives per day between the surface and 500 meters depth, producing about 1.6 Watt-hours of power each dive to operate the on-board sensors, GPS receiver and communication device.