Electric vehicles (EVs) are free running vehicles that partly or wholly use electricity for traction, whether by land, sea or air. In the sea Remotely Operated Vehicles (ROVs) use power fed from a surface vessel or from shore via an umbilical so they are not within the definition of EVs.
By contrast, AUVs rely solely on their batteries or other onboard systems to provide the power for their propulsion. The battery technology is moving forward and the power density of batteries is vastly superior to what it was even five years ago. Lithium batteries are often used that are similar to those used in land based EVs. That includes second generation lithium that is chemically proof against thermal runaways, lithium phosphate being an example of this.
Some of the larger vehicles have been tested with semi fuel cells, such as the Kongsberg Hugin, which uses a hydrogen peroxide semi fuel cell and a number of the other larger vehicles have done the same. There are limitations to the use of fuel cells, particularly with the chemicals used such as hydrogen peroxide so batteries from the same companies supplying land and EV batteries will remain favorites for the next ten years.
Deep-sea battery technology has improved. A 60 KWh deep-sea lithium cobalt battery system is now only 20 x 23 x 35" and life is greatly improved. Some are designed using lithium polymer technology to withstand great pressures at great depths. Bluefin is even designing a massive 300kWh AUV battery, far more powerful than those encountered in electric cars.
Undersea docking of an AUV to charge the batteries
Source MBARI
Bluefin pressure compensated battery packs for AUVs
Source Bluefin
The majority of underwater vehicles are powered by propellers but there is a small number that use what is known as biomimetics, which is a man made device taking the form of biological function. These include a robotic manta ray, tuna, dolphin and robotic fish for example.
"These robotic biomimetic vehicles haven't had much focused application but a number of them, such as the Manta Ray, are designed to be low power as they are of a very efficient hydrodynamic design so they can potentially perform long duration surveys and surveillance duties and environmental monitoring," states Paul Newman the offshore consultant. "It can carry a substantial payload such as sensors or whatever the end-user requires."
"All of these vehicles are, in essence, platforms for whatever purpose the end-user wants to use them for and the same base vehicle can be used for a very wide variety of applications, making them very flexible vehicles."
In summary, AUVs are used for an increasing variety of military and civil uses. The unique IDTechEx report "Electric Vehicles 2010-2010" examines many types that we have not covered in this three part series of articles as well as surface water EVs, listing 44 suppliers and their activity and prices. It forecasts global sales of electric marine craft by numbers, unit price and total market value for 2010 - 2020, explaining why the market will double in value over the next ten years.
For more see: Electric Vehicles 2010-2020 and attend Future of Electric Vehicles a global event on the whole electric vehicle market, covering all forms of EVs.
