Aalborg Universitet. Published in: Proceedings of the Fourth CA-OE Workshop. Publication date: 2006

Transcription

1 Aalbog Univesitet 3 Yeas Expeience with Enegy Pouction on the Nissum Bening Wave Dagon Pototype Figaa, Pete Bak; Te, James William; Kofoe, Jens Pete; Fiis-Masen, E. Publishe in: Poceeings of the Fouth CA-OE Wokshop Publication ate: 2006 Document Vesion Publishe's PDF, also known as Vesion of eco Link to publication fom Aalbog Univesity Citation fo publishe vesion (APA): Figaa, P., Te, J., Kofoe, J. P., & Fiis-Masen, E. (2006). 3 Yeas Expeience with Enegy Pouction on the Nissum Bening Wave Dagon Pototype. In Poceeings of the Fouth CA-OE Wokshop: Pefomance Monitoing of Ocean Enegy Systems, Lisbon, Novembe, 2006 Cooination Action on Ocean Enegy (CA-OE) : Sixth Famewok Pogamme. Geneal ights Copyight an moal ights fo the publications mae accessible in the public potal ae etaine by the authos an/o othe copyight ownes an it is a conition of accessing publications that uses ecognise an abie by the legal equiements associate with these ights.? Uses may ownloa an pint one copy of any publication fom the public potal fo the pupose of pivate stuy o eseach.? You may not futhe istibute the mateial o use it fo any pofit-making activity o commecial gain? You may feely istibute the URL ientifying the publication in the public potal? Take own policy If you believe that this ocument beaches copyight please contact us at vbn@aub.aau.k poviing etails, an we will emove access to the wok immeiately an investigate you claim. Downloae fom vbn.aau.k on: septembe 25, 2018

2 3 yeas expeience with enegy pouction on the Nissum Bening Wave Dagon Poto Type P. Figaa a, J. Te a, J.P. Kofoe a, E. Fiis-Masen b a Depatment of Civil Engineeing, Aalbog Univesity, Aalbog 9000, Denmak b Wave Dagon ApS., Blegamsvej 4, Copenhagen N 2200, Denmak Wave Dagon is a floating wave enegy convete woking by extacting enegy pincipally by means of ovetopping of waves into a esevoi. A 1:4.5 scale pototype has been sea teste fo 20 months. This pape pesents esults fom testing, expeiences gaine an evelopments mae uing this extene peio. The pototype is highly instumente. The ovetopping chaacteistic an the powe pouce ae pesente hee. This has enable compaison between the pototype an ealie esults fom both laboatoy moel an compute simulation. This gives the optimal opeating point an the expecte powe of the evice. The poject evelopment team has gaine much soft expeience fom woking in the hash offshoe envionment. In paticula the effect of maine gowth in the aft tubes of the tubines has been investigate. The contol of the evice has been a focus fo evelopment as is opeates automatically fo most of the time. This has le to impovements in the powe take off, tim contol an stability of the evice. Keywos: Wave Powe, Ovetopping, Pouction, Pototype Intouction The Wave Dagon is a floating offshoe wave enegy convete of the ovetopping type. A full scale Wave Dagon esigne fo an appopiate climate woul have an installe powe of 4-11 MW. A pototype scale at 1:4.5 of a Noth Sea moel an ate at 20 kw has been teste in Nissum Bening, a lage inlan wateway in Denmak fom May 2003 to Januay The concept woks by waves ovetopping a amp, filling a floating esevoi with wate at a highe level than the mean sea level. This hea of wate is use fo powe pouction though the specially esigne hyo tubines. Figue 1: The Wave Dagon Nissum Bening Nissum Bening Pototype. The pototype has all the featues of a opeational powe plant incluing: slene wave eflectos to focus the enegy of the waves towas the amp, a pneumatic system to ajust the floating level of the platfom; seven Popelle tubines mounte with pemanent magnet (PM) geneatos to convet the potential enegy of the wate; an an invete system to contol the vaiable spee of the tubines. Futhemoe, thee calibate ummy tubines ae use to pocess ovetopping flow ates that excee the capacity of the Popelle tubines. The powe geneate is expote to the Danish national gi via a thee phase sub-sea powe cable. Availability The Wave Dagon Nissum Bening Pototype has been teste in eal sea fo appox. 3 yeas. Duing the peio May 2003 to Decembe 2004 the availability of the system has been continuously inceasing to up to 80% at the last pat of the peio.

3 Monthly opeating expeience of the powe pouction systems fom May 2003 until en of 2004 is summaise in Figue 2. This eflects time logge in the PLC system whee the Wave Dagon s powe pouction system has been in active opeation, eithe Continuous opeation (geen) moe which coves longe peios whee the pototype has been in automatic pouction moe. Not necessaily aiming at optimum powe output. When caying out specific test uns (labelle Testing, yellow). This coves tests of contol systems an tests of hyaulic esponse, i.e. effect on floating level an stability. The aitional time has been spent on: Re-constuction an e-configuation activities (labelle Re-constuction, gey) Waiting time (labelle Out of opeation, e). This coves as an example holiays an simply evenings an nights in the peios without a woking automatic fie extinguishing systems (insuance question). In these peios powe pouction has been stoppe. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Continuous pouction Re-constuction Testing Out of opeation May 03 Aug. 03 Nov. 03 Feb. 04 May 04 Aug. 04 Nov. 04 Figue 2: Availability of WD-NB ove the peio of eal sea testing. The Wave Dagon s powe pouction system efee to coves tubines, geneatos, invetes an ectifies plus PLC system. A close to 100% availability has been achieve fo othe Wave Dagon systems, like the automatic floating level an stability system an the emote contol an communication systems. Fom the 1 st Octobe 2004 to 8 th Januay 2005 measuements wee mae almost continuously on the pototype. May 2006 the Poto Type was move to a moe expose location in the Nissum Bening. Fom May 2006 to pesent (Novembe 2006) spoaic measuements have been ae to the initial tests. Sample peios of 30 minutes wee chosen to 500 waves. This pevents too much scatte within a esult set, while peventing a loss of efinition ue to fast wave buil up in Nissum Bening which has a elatively shot fetch. Of the appoximately 4800 such sample peios uing the time 3969 ecos wee mae incluing the most impotant measuements. Of these 1577 ha high quality enough measuements to allow full time seies analysis of all the flows, an of these 247 ha significant wave height geat enough to give some powe pouction. This elatively low popotion is ue to the fact that the platfom was not fully ballaste fo safety easons an thus it neve floate at a level low enough to pemit ovetopping at vey low wave heights. These 247 sample peios ae those shown in this pape. Powe captue The wate flow ovetopping the amp an the hyaulic powe which passes though the tubines ae the two main measues use to compae powe pouction pefomance at this stage. The ovetopping flow is compae to peictions base on ealie laboatoy tests. The hyaulic powe passing though the tubines accounts fo the lowe hea acoss the tubine than the cest feeboa. The electical powe geneate by the eal tubines is ecoe. A thi measue of powe is the estimate electical powe, this is the powe which woul have been pouce

4 by the hyaulic powe if the ummy tubine flow ha passe though a functioning tubine an if the spee contol of the PM geneatos was woking optimally. The ovetopping flow is efine as the flow which passes though the tubines, ignoing any spill fom the esevoi back to the sea. The iniviual tubine flow is calculate fom the tubine chaacteistic (Kelle et al, 2001) as a function of hea an otational spee. Pessue tansuces in the esevoi measue the hea. Kofoe et al, 2006, pesents the ovetopping elationship fo the Wave Dagon. It is clea that thee is a wave length epenency on the ovetopping. The fom of the nonimensional units Q* an R* epen on the wave steepness, base on the beaking citeion. The slope of the amp of the Wave Dagon is athe steep; to avoi loss of enegy uing beaking. Figue 3: Vetical istibution of enegy A iffeent metho to inclue the fequency epenency of the waves into the nonimensional fom is given by Kofoe, Its physical basis has moe elevance fo this case of a floating ovetopping evice, an is shown above in Figue 3. The aveage ovetopping ate Q N is non-imensionalize as nomal an moifie by the atio of the enegy in the wate column between the fee suface an the aft of the evice to the total enegy in the wate column. 1 Q QN = (1) λ 3 W gh S Whee: Q = ovetopping ate [m 3 /s] H = Significant wave height [m] S W = Ramp with 21.6 m [m] λ = Ratio of enegy between fee suface an evice aft E f, to incient wave enegy E f,. [m] sinh(2k p(1 )) + 2k p(1 ) λ = 1 sinh(2k p) + 2k p k p = Wave numbe at peak peio [m -1 ] = Depth of wate [m] = Daft of evice [m] Figue 4 shows the ovetopping flow elationship, between the Q N an the elative cest feeboa (Rc/Hs). The peicte ovetopping fom the ol theoy (Hal an Figaa, 2001) is pesente to compae the flow though the tubines measue on the pototype. The scatte in these esults is ue to the iffeence in the fom of the elationship, an exponential best fit line is plotte fo these. The measue flow though the tubines is plotte, with the size of the makes inicating the popotion of time the esevoi was within 0.01 m of full. The lage points show a full level between 50 % an 75 % of the time. QN Ol theoy Rc/Hs Figue 4: Ovetopping flow Measue Flow

5 When the cest feeboa was high (Rc/Hs > 1) the ovetopping ate was geneally highe than peicte fom the ol fomulation. In lowe cest feeboa the wate flow though the tubines was consieably less than the peicte flow. In these cases the esevoi was vey close to the full level fo ove half the peio. It is pobable that this loss in flow is ue to consieable spill fom the esevoi back to the sea. This is a geate poblem than expecte as the flow capacity of the pototype was less than esigne. This was cause by an incoect setting of the invete spee contol, causing the geneatos to spin at a below optimal spee, an also thee of the geneatos wee out of oe fo this peio. The flow capacity of the pototype is thought to have been aoun 65% of the esigne capacity. Figue 5 below shows the aveage powe pouce in vaious sea states. The Pouce powe is the electicity elivee fom the PM geneatos on the woking tubines. The Estimate Powe is the electical powe which woul have pouce if the ummy tubines ha been poucing at the same efficiency as the actual tubines, an if the invete spee contol ha been functioning coectly. The Hyaulic powe is the powe of the wate passing though the tubines Figue 5: Enegy captue Thee is a significant iffeence between the hyaulic an the electical enegy. This is ue to the low oveall efficiency ( epening on hea) of the scale own tubines an geneatos, mainly ue to fixe losses such as beaing fiction. In the full scale the oveall efficiency of this stage will be between 0.80 an The total levels of enegy pouction ae also low as the platfom was mostly opeate at a too high floating level an with insufficient tubine capacity at the lowe levels. Figue 6 shows the atio of enegy captue by the Wave Dagon. The Hyaulic efficiency is efine as the atio of the aveage powe of the wate though the tubines to the theoetical incoming wave powe acoss a with equal to the Wave Dagon amp with (see Falnes, 2002). The Pouction enegy is the atio of the aveage electic powe geneate by the opeating tubines to the same theoetical incoming wave powe. Efficiency Aveage Powe [kw] Rc/Hs Figue 6: Efficiency Hyaulic Pouction Hs [m] Pouce Estimate Hyaulic

6 Fom this iagam it appeas that the optimal elative cest feeboa fo enegy pouction is aoun Rc/Hs = 1.0. The hyaulic efficiency was lowe at the lowe cest levels ue to the lack of tubine capacity. Pouction efficiency is much lowe at these points as hee much of the flow passe 0.62 m an a floating level of 0.45 m. Thee is a geat eal of ummy tubine activity hee, which oes not show up on the actual electical pouction. The powe is quite smooth, with a atio between the peaks an toughs of the estimate powe of aoun Powe [kw] Time [s] Pouction Estimate Hyaulic Figue 7: Time seies of sample eco though the ummy tubines an so i not geneate any electicity. Pevious simulation wok has shown an optimal elative floating level of Rc/Hs with full capacity. This is still believe to be accuate. Cuently wok is being conucte by Knapp in the Technical Univesity of Munich on the simulation pogam. This wok is tying to simulate the pouction of the pototype Wave Dagon, opeating as it i uing this peio, in paticula taking into account the faulty tubine spee behaviou. This will enable a goo compaison of whethe the enegy captue is ealistic, an how lage the impovement in pouction woul be if the tubines ha been opeate at full capacity. The time seies shown in Figue 7 shows a 10 minute sample fom the eco of Decembe 16 th 2004 at just afte 9 am. The coesponing point lies oughly in the mile of the ecos an was of a sample with Hs = Soft issues In opeating an maintaining the evice uing the testing peio, the evelopment team has gaine invaluable soft expeiences. This can be goupe into the following categoies: Maintenance: the expeience has shown that access to the evice, tanspotation of pieces of equipment an wok on boa ae only possible in elatively calm weathe conitions. This can be planne on the basis of weathe foecasts, but majo opeations nee to be planne incluing a withawal scenaio fo the case that the wok nees to be stoppe ue to ba weathe. Coosion: fo many stationay steel pats, a conventional epoxy paint system has poven sufficient. Fo some of the moving pats, howeve, moe expensive coosion esistant mateials neee to be use. This pove to be of paticula impotance in pats of the powe tain such as tubine shafts an beaings. Fo stongly stesse

7 components, stess coosion cacking nees to be consiee. Maine gowth: On components uneneath the wateline, heavy maine gowth has accumulate within a shot time. In some components this is acceptable, as it just means aitional weight. In othes, such as the tubine aft tubes, the laye of gowth inceases the fiction losses an euces the pefomance. This poblem was solve by using suitable non-toxic anti-fouling coatings, which pove vey efficient. Electical equipment: A numbe of components that wee classifie IP66 faile although they wee just expose to ain an win. The spay of sea wate is caie into places that seem to be elatively well sheltee. The lesson leant is that sensitive equipment must assemble with utmost cae to make sue the sealing popeties ae maintaine, an it nees aitional potection against splash an spay exposue. Also the effect of coosion attack onto the sealing sufaces nees to be consiee. Oveall, thee wee no poblems that coul not be solve, but a lot of poblems that wee not anticipate. Conclusion The eal sea testing of the Wave Dagon pototype has poven its seawothiness, floating stability an powe pouction potential. Opeation of the evice in the hash offshoe envionment has le to a numbe of smalle component failues. All of these have been investigate, an technical solutions have been foun. An enomous quantity of ata has been collecte uing the testing peio, which has not yet been fully analyse. Howeve, the wok one up to now has confime that the pefomance peicte on the basis of wave tank testing an tubine moel tests will be achieve in a full scale pototype. Looking at the peio May 2003 to Decembe 2004 an scaling the enegy pouction (1:4.5) to a typical 16 kw/m wave climate as foun in the Noth Sea the pototype Wave Dagon woul have pouce fom 50 to 500 MWh/month. Taking into account own peios an testing peios the eal pouction has been appox. 3.2 GWh/yea. The latest tests have shown that an optimal setting of the set points of the PM geneatos has incease the powe pouction with a facto 2. Theefoe it is assume that the eal pouction easily coul have been 6.5 GWh/yea o equal to an 18 % aveage waveto-wie efficiency. This esult shoul be compae to the 16 % pototype goal an the 21 % long tem goal fo the Wave Dagon technology. Measuements of the hyaulic powe inicate that it will be possible to each this value of enegy pouction. Some of the iscepancies ae believe to be ue to the scaling which will cause exta enegy losses in beaings etc. Acknowlegements The pototype poject has only been possible with geneous suppot funing fom the Euopean Commission (Contact No: ENK5- CT ), Danish Enegy Authoity, The Obel Family Tust an the eication of the paticipating patnes The fist autho is a eseach fellow fune by the Maie Cuie WaveTain taining netwok. Futhe infomation Moe infomation can be foun on the poject at the website Refeences Falnes J. Ocean Waves an Oscillating Systems, Cambige Univesity Pess, 2002 Figaa P. an Kofoe J.P. Powe pouction expeience fom Wave Dagon pototype testing in Nissum Bening: 2003 to 2005 Aalbog Univesity, Hal, T. an Figaa, P.: Foces an

8 Ovetopping on 2. geneation WD fo Nissum Bening. Phase 3 poject, Danish Enegy Agency. Poject No. ENS-51191/ Hyaulics & Coastal Engineeing Laboatoy, Aalbog Univesity, Denmak, Kofoe J.P. Wave ovetopping of Maine Stuctues Utilization of Wave Enegy Aalbog Univesity, Kofoe J.P., Figaa P., Fiis-Masen E. an Søensen H.C. Pototype testing of the wave enegy convete wave agon Renewable Enegy 31, Te, J., Kofoe, J.P., Knapp, W., Fiis- Masen, E., an Søensen, H.C.: Wave Dagon, pototype wave powe pouction. Wol Renewable Enegy Congess - IX, Floence, Italy, August, 19-25th, Kelle J., Rohne W., Böhm C. an Knapp W. Wave Dagon, Development an Tests of a Vaiable Spee Axial Tubine TU München, 2001.