FRAUNHOFER INSTITUTE FOR WINd ENERgy ANd ENERgy SySTEm TEcHNOlOgy IWES. wind energy report germany 2012

Transcription

1 FRAUNHOFER INSTITUTE FOR WINd ENERgy ANd ENERgy SySTEm TEcHNOlOgy IWES wind energy report germany 2012

2 publisher: Dr. Kurt Rohrig Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) Division Energy Economy and Grid Operation Königstor Kassel / Germany windmonitor@iwes.fraunhofer.de Editorial team: Volker Berkhout, Stefan Faulstich, Philip Görg, Paul Kühn, Katrin Linke, Philipp Lyding, Sebastian Pfaffel, Khalid Raik, Dr. Kurt Rohrig, Renate Rothkegel, Elisabeth Stark Consulting Dr. Jutta Witte (editorial ofice Surpress) Cover photo acknowledgment: Siemens press picture Copyright: All rights to reprint, use imagers, reproduce in a photo mechanical or similar way and to save information in data processing systems remains the right of the Fraunhofer IWES and their employers.

3 Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) division Energy Economy and grid Operation wind energy report germany 2012 Volker Berkhout, Stefan Faulstich, Philip Görg, Paul Kühn, Katrin Linke, Philipp Lyding, Sebastian Pfaffel, Khalid Raik, Dr. Kurt Rohrig, Renate Rothkegel, Elisabeth Stark

4 WIND ENERGY REPORT GERMANY

5 Special Report extended operation of wind turbines Beyond their planned service Lives Jürgen Holzmüller introduction In the relevant regulations (DiBT guidelines / DIN EN ), it is stated that The design life of a wind turbine must be at least 20 years. In general, wind turbines for onshore are designed for an operating period of exactly 20 years, because each design year more 20 years would mean increased manufacturing costs and hence a higher sales price for a wind turbine Usage period in years Planned service life Extended service life The design life is a theoretical parameter and is also termed the planned service life. The load-bearing capacity of the structure and suitability for use must be demonstrated for this period. At the end of the 20 year period there is generally an interest in continuing to operate the wind turbine beyond this period. After all, disassembly and disposal at the end of the planned service life goes against the philosophy of sustainable usage. Further operation can, however, only be tolerated if safe operation is guaranteed within the extended service life. On the other hand, further operation is only desirable if the resulting revenues exceed the costs for operation and maintenance. Figure 1 shows the time periods under Eurocode 1 which play a role here. Start-up Total usage period Figure 1: Schem tic of the time periods Decommissioning and disassembly aspects for consideration during the residual/ extended service life period When operating a wind turbine during the extended service life period, various aspects must be considered: administrative and legal aspects. Approvals for construction are generally subject to a requirement whereby further operation after expiry of the planned service life must be demonstrated by additional tests on the stability and suitability for use of the relevant wind turbine. It must be assumed that such tests will cert inly be required in the future. The ofici l principle puts safety foremost. From a current point of view, it cannot be ruled out that other, as yet unknown requirements are imposed by the relevant authorities in order to guarantee safe operation during the extended service life period. These will naturally have costs associated with them. Leases and use contracts are sometimes only entered into for the planned service life period. It must in ll c ses be cl riied whether the relev nt contr cts apply, without restriction, for the total usage period. P vo Bl ield 79

6 WIND ENERGY REPORT GERMANY 2012 technical aspects. Further operation can only be tolerated if safe operation can be guaranteed during the extended service life period. Suitable procedures and guidelines are currently being developed to enable the continued operation of wind turbines which have reached or will soon reach their 20 year service life. In the longer term these procedures will naturally also be available for wind turbines which only reach the end of their 20 year service life in a few years time or further into the future. economic aspects. At the start of and during the extended service life period extra costs arise for testing, close monitoring, in some cases installation of monitoring systems, and possibly also the overhauling of individual components. Income security also decreases at the start of the extended service life period because currently the REA only guarantees the minimum remuneration for 20 years. potential for an extended service life The probability is very high that a wind turbine can be used for a total period that is longer than the design life. The initial experience is that extension is usually possible. Figure 2: Principle of f tigue Assumed average wind speed over 20 years for theoretical calculations T ble 1: Effect of the ver ge wind speed on the tot l us ge life of wind turbine Actual average wind speed at the location over 20 years Wind load zone 3 Wind load zone 3 Potential extension after 20 years of operation No extension possible Wind load zone 3 Wind load zone 2 ca. 3 to 6 years Wind load zone 3 Wind load zone 1 Probably > 10 years The theoretical fatigue test for wind turbines is based on the following general boundary conditions: Technical availability of the wind turbine of 100%. Average wind speed according to the wind class under DIN IEC or the wind load zone under the DiBt guidelines. Turbulence class according to DIN IEC Constant loads for 20 years. The theoretical calculation gives a quasi overall or maximum cumulative load. If a wind turbine at a location is actually exposed to lower average wind speeds or lower turbulence or has lower availability, then the components are subjected to correspondingly lower operating loads. If components, in reality, are exposed to lower lo ds during the irst 20 ye rs th n were ssumed for the theoretical calculations, then these components will not be fatigued and further operation of the wind turbine will be possible from a technical standpoint. Further operation 80

7 Special Report Extendes operation of wind turbines beyond their service lives c n be extended until the components in lly do ctu lly re ch their f tigue limit. Figure 2 cl riies this situ tion. The section below gives a roughly estimation of how long extended operation is generally possible. If a wind turbine has a technical availability less than 100%, then there are downtimes during which there are very low or negligible fatigue loads. If a wind turbine was 100% available for 20 years this would amount to 175,200 operating hours over that period. If, however, a wind turbine is only actually available for 95% of the time, then after 20 years this wind turbine totals only 166,440 operating hours. The potential extension of service life is thus the order of ca. 12 months. If lower average wind speeds prevail at the actual location than assumed for the theoretical calculations, then the wind turbine components are exposed to lower loads and hence less fatigue. Rough estimation gives the prospective extension in Table 1 of the service life. If, for example, the wind turbines are all suitable for locations in wind lo d zone 3, then for ll loc tions in wind lo d zone 1 and 2 there is in principle the potential for extension of the service life. Turbulence h s n inluence on the f tigue beh vior of components of wind turbines: The higher the turbulence the greater the fatigue. In general, wind turbines are designed for the highest turbulence level because only then can it be guaranteed that the wind turbines can be erected at any desired location in Germany. For certain, not all wind turbines are exposed to the highest level of turbulence and as such many wind turbines experience less fatigue. Regarding turbulence, the hub height and wind f rm conigur tion pl y role. Enh nced turbulence on caused by upwind wind turbines must be taken into account. Wind load zone Figure 3: Wind lo d zones in Germ ny /DIN1055-4: / Wind speed 22,5 m/s 25,0 m/s 27,5 m/s 30,0 m/s Quantitative calculation of the potential service life extension is only possible for speciic loc tion t king into ccount the speciic loc l turbulence nd situ tion. As the potenti l service 81

8 WIND ENERGY REPORT GERMANY 2012 life extension is based on various factors, the extension period for each factor can be cumulated. Three case examples will demonstrate this. Figure 4: Extr ct from the guidelines of Germ nischer Lloyd for the extended oper tion of wind turbines (version 2009) Case example 1: A wind turbine, designed for wind load zone 3, is built along with two other wind turbines at a location in wind load zone 2. The 3 wind turbines stand in a line and are positioned transverse to the prevailing wind direction. The turbulence at the location is in the average range. The wind turbine attains an average availability of 97% after 20 years. Rough calculation shows there is a possible service life extension of ca. 4 to 7 years. Case example 2: A wind turbine, designed for wind load zone 3, is built alone at a location in wind load zone 1. The surrounding area is relatively l t nd the turbulence t the loc tion is low. The wind turbine attains an average availability of 95% after 20 years. Service life extension of more than 10 years is possible. Case example 3: A wind turbine, designed for wind load zone 3, is built in the fourth row of a wind farm in the direction of the prevailing wind at a location in wind load zone 3. The surrounding area is complex, namely there is relatively high turbulence. The wind turbine attains an average availability of 98% after 20 years. A realistic service life extension of a few months is possible. measures to guarantee safe operation during the extended service life As wind turbines are generally designed for a service life of 20 ye rs, the further oper tion of the wind turbine beyond the 20 ye r period requires me sures to gu r ntee s fe oper tion and so rule out risks to the environment. It must be borne in mind here that extension of the service life cannot be automatically extended per se to a particular type of wind turbine, rather each individual wind turbine must be tested to ensure it meets the required criteria. This even applies for wind turbines which re loc ted next to e ch other in the s me wind f rm. Figure 4 shows which inspections must be undertaken for this. 82

9 Special Report Extendes operation of wind turbines beyond their service lives Analytical methods are understood to mean calculation methods with which ny d m ge c n irst of ll be determined and, based on this, the extended service life estimated, assuming the actual damage has not reached the maximum permissible damage. These include methods as previously described elsewhere. The practical methods involve determining the actual state of the components by inspection and evaluating any risks by carrying out failure analysis. Further operation of the wind turbine is only possible if risks can be ruled out based on the failure analysis and inspections. As both the analytical calculations and practical methods yield valuable information for further operation of the wind turbines beyond 20 years, the revised DiBT guidelines (in the future deinitive for found tion structures) describe the use of both approaches. Our current knowledge does not allow prediction of the total usage life of a wind turbine with high probability of occurrence. As such, the results presented here are only rough estimates. Over the coming years experience will be gained, leading to improvement of the forecasting models. Technology for service life monitoring for wind turbines is current being developed. This technology will allow exact recording of re l lo d luctu tions nd ny resulting d m ge. Thus in the near future a forecasting instrument for extension of the service life will become available. This is likely to lead to signiic nt extension of the service lives of m ny wind turbines, with simultaneously minimization of overhaul costs. Besides the analytical determination of the current status, alternative measures to overhaul components or additional measures for online monitoring of the health of a wind turbine can also be carried out: Overhauling here is understood to mean constructional measures to improve the stability of a wind turbine and hence extend the service life. The continuous health monitoring of components using sensors over the 20 year service life period may enable more accurate forecasting of the actual moment of failure than can purely theoretical considerations. Outlook The matter of extension of the service life of wind turbines has only been discussed in relatively recent times and as such the guidelines, information, and procedures that are available are not fully established. The future will bring further research indings which m y le d to signiic nt ch nges to processes nd procedures. 83

10 Fraunhofer iwes Kassel Königstor Kassel / Germany Phone: Fax: Fraunhofer iwes Bremerhaven Am Seedeich Bremerhaven / Germany Phone: Fax: info@iwes.fraunhofer.de Funded Supervised by on the base of an act of the German Parliament by Federal Ministry for the Environment, Nature Conservation and Nuclear Safety