Calculations of pump efficiency for wave-powered WEPAB show a relatively significant flow with a mean of 0.34 m3/(s m) even if assuming uncertainty interval ranging between 50 - 90 %. However, a challenge for full-scale systems is assimilate the vast energy present during storms (which corresponds to the 90% percentile) while also being effective at more normal wave conditions. The performed demonstration and monitoring as well as related activities can be used for the further development.
As already mentioned, results from the project indicate that full-scale pumps needs to have a certain minimum size that depends on the current wave parameters in the region of application. This is necessary to prevent the pump from riding the waves. Further, the slope and freeboard has to be adjusted for each wave characteristic. This would increase pump efficiency and reduce stresses on the anchorage and the vertical pipe. In addition, also the water intake principle can be improved without significant changes in costs. The cost of oxygen pumps can be divided into different parts: manufacturing, installation, de-installation, maintenance and operation. In contrast to the demonstration units used in this project, there is no need for measurement equipment on the module itself. Each module must be equipped with offshore safety marking. Some things can be improved based on experience from the prototypes, e.g. the pipe connection and anchorage. Since the size of a full-scale oxygen pump is not defined cost calculation was based on the pilot plant WEBAP I with a width of 14 m. The production would amount to around 1-1.2 MSEK. Considering the production of multiple devices would reduce unit costs significantly.
This cost can be compared to the module's efficiency which would likely much higher for a full-scale plant than for the used prototype because of an improved efficiency by avoiding “riding the waves”, a rougher wave climate in the open sea and with regard to constructive improvements.
Several suggestions for improvement of WEBAP concept and design have come up during the project, both the project itself and third parties. One of these is to utilize even small waves by adding the intake just below the water surface and using the pressure difference as a control parameter. When an overpressure due to the incoming wave crest occurs outside the valves the water rises inside the basin. When the pressure at wave trough becomes bigger on the inside, the valves closes and the water flows down through the tube.
The fact that the wave-powered oxygen pumps of type WEBAP I would be more effective when they are built with large dimensions opens for another option to combine oxygen pump with other offshore structures.
Figure. Concept of a possible full-scale application and design of WEBAP I as an independent unit or in combination with other offshore structures (here Hexicon offshore wind; www.hexicon.eu).
For areas without access to the waves, the electric oxygen pump consisting of one or more modules can be the only alternative. The electric oxygen pump WEBAP II contains apart from the tube mostly standard components and a full-scale plant would thus consist of similar parts. Cost analysis can therefore largely based on the existing pilot plant although a full-scale plant should be operated preferably with green electricity, biofuels, biogas, biodiesel, ethanol, etc. Figure 3.13 shows a possible full-scale facility consisting of three pumps of the same type as used for the prototype, a simple control system and working platform that enables service year round and protects the structure from ice. When using standard components for example floating pontoons etc. such a full-scale plant would, based on estimations from companies that have been involved and constructed the prototype, cost about 700 -800 kSEK. However, in contrast to wave-powered oxygen pumps a larger operational cost for electricity or biofuel and service of pumps is required. On the other hand, a stable and controllable pumping can be achieved.
Figure. Concept of a possible full-scale application and design of WEBAP II - Electric oxygen pump with three pumps in combination.
The pump is a development of the company Inovacor AB and can be seen as a further development of WEBAP concept, which combines the advantages of WEBAP I and II. Although this pump makes use of wave power as WEBAP I it utilises wave energy with the help of a moving float that follows the wave motion. The pump is based on a new pump technology DAPP (Dynamic Adaptive Piston Pump) that originates in a basic discovery about the real heart pumping and control functions, and that is very resource efficient. Even at small waves (~ 10cm) a flow is generated by the pump. In the same manner as WEBAP II it allows to take in water from different depths. Other benefits which have been tested during pilot tests are that the vertical pipe does not follow the movement of the float but is fixed providing an even more robust design. The anchorage is centred in the structure, which reduces wear and tear on the pump.
The development of this type oxygen pump was initiated by WEBAP activities and a side-development of an on-going compact wave energy project www.corpowerocean.com. The pump has a very high efficiency and created a continuous flow. Up-scaling calculations and cost calculations from the wave power project indicates that the production of a standard unit for 3-5 m3/sec and 0.05 bar pressure, and 100 meters depth requires an average power of about 25 kW and peak power of over 100 kW. Investment cost including installation of such a unit should be less than 500 kSEK. The design of the pipe is the most uncertain cost item. At 50 % utilization over a year around 80 km3 of surface water can be pumped down to the anoxic bottoms. At smaller difference between surface water intake and water outlet can more than double this amount.
With the contribution of the LIFE financial instrument of the European Community