AN AUTONOMOUS WAVE-POWERED ENERGY SYSTEM FOR NET-PEN AQUACULTURE, BY DALLAS MEGGITT & TORE GULLI12 Jun 2014
Aquaculture operations in net pens began and have continued in relatively sheltered waters for obvious reasons. However, as aquaculture has become more intense, space and environmental issues are creating limitations to growth of netpen aquaculture due to questions of sustainability and high concentrations of biomass in restricted areas of water. These limitations have created the impetus for aquaculture operations to adapt to deeper, offshore waters. Consequently, the resulting ripple effects of less-protected, deeper waters require more robust pens and mooring systems, and changes to operating practices.
One element of the implications of aquaculture operations moving into deeper water farther offshore is more expensive cost of providing power for feeding and monitoring of fish pens. Current systems generally are diesel powered, which requires refueling and maintenance by personnel transiting to the operation, which will increase as operations move further offshore. In addition, the aquaculture operations (feeding, removal of dead fish and monitoring of the fish pens) also will require longer and therefore more costly transits for personnel.
To maximize efficiency and minimize costs, offshore aquaculture operations will require autonomous, locally powered operations and monitoring. Autonomous means that the system is self-powered (not cabled to shore), and is unattended for routine operations. Unattended means that the system can perform for extended periods without maintenance, repair or resupply of consumables. Currently-available monitoring equipment, such as above- and below-water cameras (visual, IR, or thermal), acoustic, water chemistry and other sensors can provide continuous detection, assessment and alerts for surface and subsurface monitoring. Autonomous communications systems can use RF transmissions (e.g., extended WiFi such as SeaFi) to transmit data and report event alerts. Sensors and communications systems that can be adapted to these applications are commercially available.
The availability of reliable, long-life wave energy conversion technology, low-power sensors, and low-power local computer processing combine to make autonomous, self-powered, longlife operating and monitoring systems that can be installed and operated as part of an offshore aquaculture operation. The technology is available to develop and demonstrate such an operating system.
This system will have the following four key system features:
• Self-powered, using a demonstrated reliable, high-operational availability wave energy technology, with on-board energy storage, suitable for use in all water depths of interest
• Hybrid configuration, with combined wave energy, storage, and diesel backup • Autonomous, unattended operation with very high mean time between failures and high operational availability (goal mean time between failure of 1 year; goal operational availability(i.e. producing power) of 90 percent)
• Processing of sensor data with defined event alert thresholds (equipment malfunction, breach of nets, others).
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