Submersible Annular Generator (SAG) is a key component in a family of marine and hydrokinetic devices jointly developed with and for Ocean Energy Industries, Inc. and Vortex Hydrokinetics LLC.
SAG is a low-speed synchronous large diameter ring style multi-pole generator with permanent magnet excitation. In contrast to electrical excitation, permanent magnet technology does not have the disadvantage of additional excitation losses. The savings in excitation power are thus fully available as additional energy yield. Output voltage and frequency vary with the speed and are converted for output to the grid via voltage and frequency stabilizing equipment which allows for speed variability.
SAG requires no hermetic enclosure and provides an almost frictionless flow of energy, while fully submerged in water. Smaller number of moving components assure minimal material wear. Unlike conventional fast-running generators, SAG is subjected to little technical wear, making it ideal for particularly heavy loads and a long service life.
Unlike traditional generators used in hydro, wave, tidal and ocean current energy converting devices, SAG requires no protection of hermetically sealed container, no magnetic couplings, no petroleum-based lubricants, no special cooling measures. SAG is cooled and lubricated by the water in which it is submerged. The copper winding in the stator (the stationary part of the annular generator) and the permanent magnets in the rotor (the rotating part of the annular generator) are fully enclosed in plastic and resin, and therefore completely insulated from water.
Traditional generators need a rotation speed of about 1500 rpm to generate grid quality electricity. However, a typical large wind turbine rotates at less than 30 rpm. A typical tidal turbine rotates at less than 10-60 rpm. WaveSurfer and WaveSailer wave energy converters deliver less then 10-15 rpm. Traditional designs require complex and expensive gearbox in order to increase the speed to 1500 rpm. The inner components of the gearbox are prone to tremendous stress. SAG eliminates gearbox thus reduces cost, simplifies maintenance and drastically reduces energy losses.
The functionality and survivability of equipment in an underwater environment demands simplicity and robustness. SAG meets these demands, with its slow-moving rotor and lubricant-free operation minimizing risk to marine life.
SAG has a design life of at least 20+ years without significant service expenses.