Floating wave power plant
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Floating wave power plant Floating wave power plant Document Transcript

  • FLOATING WAVE POWER PLANT INTRODUCTION: The oscillating water column (OWC) principle is an attractive approach to convert wave energy into electrical energy as exemplified by operational plants in several countries [1]. As of today it is reasonable to expect a wave to wire efficiency of about 24 % with a fixed OWC device [2]. Of this, the OWC efficiency would be about 60 %, and the power module (comprising bidirectional turbine and generator) would be about 40 %. One aspect of the fixed OWC is that the structural cost could lie between 70 to 85 % of the overall cost [3]. This has motivated the development of floating OWCs which promise reduced cost with an accompanying reduction in efficiency in the hydrodynamic stage. The largest of such structures was the Japanese Mighty Whale [4]. While laboratory results predicted a best efficiency of 50 % in the hydrodynamic stage, practical measurements showed that the best efficiency was about 30 %. Hence the overall wave to wire efficiency was closer to 15 %. There have been continuous attempts to improve the efficiency of floating OWCs and the backward bent ducted buoy (BBDB) is one such attempt [5]. In this work we show that an improved power module for the BBDB with variable speed twin unidirectional turbines can achieve 65 % efficiency and thus make the floating structure attractive in spite of the lower hydrodynamic efficiency. PLANS FOR IT`S FUTURE PRODUCTION: A new Oregon company will announce Thursday plans to commercialize and manufacture floating power plant technology that generates electricity from waves and wind. Floating Power Inc. is a joint venture between Lake Oswego-based boutique merchant bank BridgeWorks Capital and Floating Power Plant Inc., a Danish company that spent the last 12 years developing and testing the power-generating platform called "Poseidon." The Poseidon generates hydraulic power from waves that interact with floats, as well as electricity from wind turbines mounted atop the platform. The electricity it generates is transported to the grid via underwater cables. Waller said the technology thus far is capable of producing enough electricity to power 15,000 homes from a single platform.
  • The company will likely have an initial test module working in conjunction with Oregon State University-based Northwest National Marine Renewable Energy Center, POSEIDON 37: It is both a floating support structureforwind turbines and a wave energy device. The concept of the Floating Power Plant is so far the only one known in the world that has combined the two energy forms and has an operating prototype. This article will describe the design of a floating support structure that combines the energy forms, but since the Floating Power Plant is the only one using it, the article will mostly refer to and describe the Floating Power Plant. The current prototype is called Poseidon 37 – the number refers to the width of the structure. Definitions When combining wind and wave energy devices, the support structure acts as a semi- submerged structure. For Poseidon, the structure is three-quarters submerged. Semi- submerged structures are sometimes referred to as barge floaters, but to avoid confusion this term will not be used. The wave energy device could in theory be of various designs such as the point absorber or overtopping terminator. But in the case of the Floating Power Plant the wave energy device is the so-called Front Pivot Hinged Wave Absorber. The wind turbines are defined by the height of the tower. This height is determined by the dimensions of the support structure. To put it in another way: the larger the platform, the higher the tower. The turbines can be either of the upwind or downwind type carrying one, two or three blades on the rotor. Depending on customer needs, there can be from 1 to 3 turbines on the platform. Why combine wind and wave? Whether one has a starting point in the wind industry or in wave energy, the logic behind a combination of the two energy forms is that it increases the return. The benefits of adding a wave energy device to a floating support structure for a wind turbine is stability and the boat landing.
  • The wave energy device absorbs the wave motions, and thereby makes the structure even more stable. According to FPP, 70-90 percent of the energy in the wave motion is absorbed into a controlled system. This provides stability compared to a normal floating structure without any absorption. And because of the absorption of the motion energy of the waves, there will always be calm waters at the rear of the structure – a lee side, where boat landing on the structure is possible in harsh weather. See the second picture below for an illustration of this. From the other point of view, the benefits of adding one or several wind turbines to a floating wave energy device are stability and increased production. Measurements from the prototype Poseidon have shown that the pressure from wind on the turbines stabilizes the structure in the water, and this stability increases the power output of the wave device by 1-2 percentage points. And since the wave energy device provides a floating support structure anyway, the cost of establishing wind turbines offshore in this system corresponds to the expense of establishing the turbines onshore. STRUCTURE: When using a semi-submerged structure for a wave energy device, the structure is modified radically compared to a standard barge. On the Poseidon 37, three sections constitute the barge: The front section, which contains the turret mooring, the middle section carrying the wave absorbers, and the rear section. The whole structure is 37 meters wide and 25 meters long (excluding the buoy). The middle section can be disconnected from the front, and the energy device can thus be sailed to port without interfering with the mooring. This is needed since the P 37 is a prototype and a test facility. The front and rear sections ensure that the Floating Power Plant always turns against the wave front – and that it does so in a passive way without consuming energy.
  • The wave absorbers (floaters) are hinged at the front. The floaters absorb the pressure motion of the wave both forwards and upwards. Up to 34 percent of the incoming wave energy is converted to electricity in the Floating Power Plant. According to FPP, this has been confirmed by the research and consultancy organization DHI (Danish Hydraulic Institute) in the latest wave flume test series. Each absorber on Poseidon 37 weighs 4.7 tonnes without ballast and 24 tonnes fully ballasted. The ballast system is an active control system. Along with trimming of the submerged depth, these are the only two active controls in the whole structure, thus the only part where energy is consumed. Ballast is used to secure the optimum floater movement: in this way the floaters have high efficiency in small as well as large waves. NEXT STEPS: The next step is the construction of a power plant of 110 meters width to be installed in Oregon, USA. A collaboration between Floating Power Plant and American venture capitalists was announced in April 2011, and the new prototype will be installed between 2014 and 2015. The largest scale of the Floating Power Plant will be 230 meters wide and mounted with three 2 MW turbines. The wave energy device will have a rated power of approximately 5-6 MW. The yearly production will be 50 GWh – of this 60-70 percent will be produced from wave energy, because the waves represent a more stable energy source, says Floating Power Plant.