System Operation
SurfPower is designed to optimally recover both potential and kinetic energy from waves. The wing shaped pontoon uniquely engages waves over a wide front, thereby maximizing energy recovery.
Seawater or fresh water is the energy transport medium used by SurfPower, thereby eliminating all risk of pollution due to accidental spills. Pressurized water is collected from a number of pontoon/pumps and delivered onshore where it is used to drive a pelton/ turbine generator and/or a reverse osmosis desalination plant. The system can be operated in a number of different modes. If driving a reverse osmosis desalination plant is required, in addition to generating electrical energy, then the system will be operated essentially at a constant hydraulic pressure with an open loop configuration (the discharge from the pelton turbine and reverse osmosis plant is simply returned to the sea). If only electrical energy is required, one of three modes can be selected to deliver the lowest cost of energy dependent on individual client needs:
- constant pressure and constant alternator speed
- variable pressure and variable alternator speed
- dual pressure and constant frequency
All of these options can be operated either open loop (discharging to the ocean) or closed loop, where the turbine discharge is piped back to the pumps.
SurfPower pontoons move when the buoyancy force generated by an oncoming wave is sufficient to overcome the pressure in the main, after which the pontoons move in response to wave action. Optimally, pontoons are configured to just have sufficient buoyancy to overcome the restraint provided by the piston pump/main’s pressure. Ideally, the pontoon will be almost totally submerged as the wave advances on to the pontoon. After passage of the wave crest, the pontoon breaks out on the backside of the wave. The weight of the pump cylinder attached to the underside of the pontoon provides a force component to guide the pontoon back to its initial starting position in the wave trough.
The piston pump is attached to the pontoon at a point approximately 3.5 meters below the center of buoyancy. The distance between the point of attachment and the center of buoyancy provides stability to the pontoon under aggressive wave conditions, i.e. when the pontoon is approached by a steep-fronted breaking wave and/or when the pontoon is totally submerged by a wave that overtops it. It is not economically viable to provide hydraulic cylinder extension sufficient to handle all wave heights that may be encountered. Optimal cost of energy will be realized if the cylinder stroke length is limited, so that the pontoon is overtopped in all wave conditions exceeding 4 meters. Pontoons are designed to withstand total submergence when they are overtopped by waves higher than 4 meters. Extra piston pump stroke length is provided to accommodate changes in the mean water level due to tidal action.
Forces on the pontoon under extreme storm conditions are mitigated by increasing the operating pressure of the system (constricting the pelton nozzle orifices). In this condition, the buoyancy of the pontoons is not sufficient to overcome the resistance provided by the piston pump and the pontoons therefore remain submerged for most of the wave cycle, allowing the high energy wave crest to move over the pontoon without impact (as shown by the video on the home page CLICK HERE).
Scientific readers are encouraged to click on Parametric Design Study for a detailed analysis of system energy recovery performance and storm survival strategy.
