A wave-powered pumping system, developed in Ireland, has been deployed in the Shannon Estuary. The system is designed to deliver high-pressure, prefiltered salt water to a reverse-osmosis (RO) desalination system. Designed to operate in a sea having an average wave height of 1.5 meters and an average period of 7.5-seconds, the 40-meter long, 4-meter wide system will pump approximately 275,000 cubic meters of salt water each year to a RO plant at an operating cost of $0.25 per cubic meter or $0.95 per 1,000 U.S. gallons. The systems, called the McCabe Wave Pump (MWP), is self-contained and, therefore, is ideal for remote locations. The need for potable water over the globe has become critical in recent years. The reasons for the water crisis are debatable. Possible causes include global warming, fertilizers and pesticides that contaminate surface waters and aquifers, and the increase in the world population. Although there is much attention given to the water-shortage problem, there is surprisingly little attention given to possible solutions. One system that has been developed to address the water problems of both the island and remote coastal communities is the McCabe Wave Pump, developed in the Republic of Ireland. As the name implies, the system is designed to pump large volumes of salt water at high pressures. The primary product of this pumped water is potable water, although the pumped water can be used to drive electrical generators. For potable-water production, a RO-desalination system is required. The RO system can be located either on shore or on a neighboring barge, depending on the location of the wave resource. A prototype of the MWP is now deployed in the Shannon Estuary approximately 500 meters offshore from Kilbaha, Ireland, on the Southeastern County Clare Coast near Loop Head. The 0.5-meter diameter water pumps are mounted between barge pairs: three between the forward and inertial barge and two between the inertial and after barge. The pumps are excited by the relative pitching motions of the barges. The pumps draw in seawater, pump the salt water through a prefilter and conditioner and then into an RO desalinator. An electrical co-generator can be designed to smooth the flow to the plant. For RO filtration, the minimum threshold pressure is approximately 23 atmospheres. The design sea for the system, one having an average wave height of 1.5 meters and an average period of 7.5 seconds, are the conditions that are found in most locations along the East Coast of the contiguous United States. Operating in this design sea, the MWP should pump about 275,000 cubic meters per year of filtered salt water (supply water), or about 750 cubic meters per day (0.0087 cubic meters/second) at an average operational pressure of about 70 bar. About 35 percent of the total supply-water volume pumped to the RO plant is desalted. Hence, approximately 65 percent of the high-pressure brine can be used to drive an electrical generator. This represents about 40 kilowatts of power available to the generator. Operating at a busbar efficiency of 75 percent, 30 kilowatts would be available to either the busbar or a battery-storage system.
