Government/Military - National Defense, Anti-terrorism, Anti-smuggling, Port and Harbor Security, Transportation Safety, Energy and Transportation

Scientific/Environmental - Climate Science, Oceanography, Meteorology, Water Quality Monitoring, Tsunami Warning, Resource and Bathymetric Survey, Sanctuary Management, Security, and Patrol, Climate Science (CO2 Flux), Marine Mammal Monitoring

Industrial - Natural Resources Discovery, Water Quality Monitoring, Fisheries Management, Aquaculture

There are no functional persistent surface vehicles currently on the market.  Government and civilian users have many requirements for a persistent presence over wide ocean areas that can only presently be met with manned vessels that require complicated logistics and great expense.  All current unmanned surface vehicles require externally supplied energy for missions of longer than a few days.  

But many ocean observation tasks require equipment to be positioned at the sea surface for long durations.  For these tasks a large number of small, low cost, observation systems tend to be used.  Without an anchor, currents and weather will tend to pull a surface vehicle, requiring energy to resist these effects.  The problem worsens as vehicle size decreases, so a small vehicle must harvest energy from the environment to maintain its position indefinitely.