The rise of a shining star in wind measurement technology

Transcription

1 PROFESSIONAL ARTICLE November 2015 The rise of a shining star in wind measurement technology A German consultancy spreads knowledge about the benefits of innovative LiDAR technology

2 The rise of a shining star in wind measurement technology A German consultancy spreads knowledge about the benefits of innovative LiDAR technology Besides a reliable estimation regarding development and operation cost figures, the basic question to be answered for the successful development of a wind energy project is about the expected yields. For the precise definition of future energy yields a well-planned wind measurement campaign is a decisive precondition. This includes the use of state-of-the-art measurement equipment to be assembled and installed by experienced personnel. Especially at larger and complex project sites or if the existing wind data basis is unsatisfactory, project risks and uncertainties can only be reduced by means of a sophisticated measurement campaign. The use of a single standard met mast is not sufficient to display the complete picture of the wind situation, especially at larger project areas or if the planned turbines hub height significantly exceeds 100 meters. What impact the application of modern LiDAR (Light Detection and Ranging) devices can have regarding a comprehensive analysis of the wind farm s potentials is discussed in the following article. Only a couple of years ago, the application of LiDAR technology for wind measurements was quite new to the wind industry. Nowadays more than 1000 wind LiDARs are already being used globally, which means a doubling of its application in the past three years [1]. Still most of the devices are operated in the more mature wind markets where experience has caused higher risk awareness on the investor s side. But also in up-coming markets like Brazil, developers already search for optimized solutions for risk and uncertainty mitigation. That LiDAR technology has the potential to substantially improve yield calculations is verified by research works, as e.g. within the framework of the UpWind project [2; 3] and numerous other studies. Regarding the acceptance of LiDAR measurement data as basis for the elaboration of bankable energy yield assessments Germany is a forerunner. With the inclusion of stand-alone LiDAR measurements in the so-called TR6 [4] a decisive step was taken in Advantages in practical application But how does LiDAR perform in every-day business? One of the wind resource experts already having gained considerable experience with the technology is BBB Umwelttechnik GmbH (BBB), a German engineering consultancy, which was founded in BBB s Bavarian branch office is accredited according to DIN EN ISO/IEC 17025:2005 for wind measurements by means of anemometer and remote sensing technology. As one of the first wind consultancies in Germany, BBB has purchased a LiDAR device in 2011 to offer it as an alternative and in addition to classical anemometry (i.e. cup anemometers mounted at a met mast) and for internal research purposes. At present BBB owns a total of six LiDAR systems and also operates external devices. With a total of 15 years of accumulated measurement time at 29 different and predominantly complex sites, BBB is to be counted under the leading experts in this technology. In order to make the system independent from a power grid, BBB s LiDAR devices are installed in small trailers which are equipped with PV panels, fuel cell and battery. Thus the devices can easily be relocated within the project site. The comparatively low power consumption of the Windcube v2 (Leosphere) enables the off-grid solution and its flexible application at the remotest sites. Another advantage of LiDAR technology is that it is apt for measurements within forested areas. Because LiDAR devices have a narrow beam angle it is not necessary to cut down as much trees for the measurement station as it is the case with SODAR measurements. Furthermore LiDAR measurements are not negatively influenced by forest sounds like rustling leaves. Wind LiDARs are generally promoted as being easy deployable for any briefly trained person. Thomas Latacz, head of BBB s wind measurement department and a widely recognized expert in the field of Remote sensing

3 technology for wind energy purposes has tested and analyzed various laser-based systems offered on the market. He knows about the limits of the technology and what is to be observed in its practical application: With a proven accuracy of nearly hundred percent LiDAR certainly opens up new horizons for the wind industry - but there a still many things to be observed for the acquisition of satisfactory data bases says Latacz. The average system availability of 99,4 % of our LiDAR measurements, for instance, has been achieved due to the Measurement Monitoring System (MMS) which was developed in-house at BBB and allows a permanent supervision of measurements. More precise data for more precise wind flow models Regarding the proper application of Remote Sensing Devices (RSD, meaning LiDAR and SoDAR measurement systems) DNV published a guideline in 2011 [5]. It is a collection of rules for best practices, ensuring that the compiled RSD data are useful for reducing uncertainty in energy yield assessments. If those rules are observed, a LiDAR device that is relocated to measure the wind at various points in the project area can substantially help to gain knowledge and certainty about the actual wind situation, especially when combined with a met mast. Horizontal cross predictions between mast and a flexible LiDAR system can assure that the theoretical model (i.e. either linear models like WAsP for simple terrain or CFD models for complex sites) delivers realistic estimates of the energy yields. Potential deviations of the model can thus be detected and adjusted and uncertainties can be diminished. This provides major advantages compared to a measurement campaign conducted with a sole met mast. In Tab. 1 results from an actual BBB project are shown illustrating the project s history. It is about a combined measurement campaign with a fixed wind met mast and two accompanying LiDAR measurements. One benefit is the information on the shear for the extrapolation up to the planned hub height and the decrease of the associated partial uncertainty for the vertical extrapolation. Secondly it allows a horizontal cross prediction between the mast and the second LiDAR position. That facilitates the calibration of the theoretical flow model until it performs more realistically in the horizontal extrapolation. This scenario clarifies the benefits with regard to reduction of uncertainty and more accurate energy yield prognosis (P75) which obviously results in an increased project value. This scenario also depicts another very important benefit of LiDAR measurements, i.e. the possibility to measure up to 200 meters above ground level and even higher, thus covering the whole rotor swept area of even the highest turbines. Erecting masts covering the whole rotor length is very expensive and under certain conditions not feasible. Therefore, an additional LiDAR measurement that is used for the vertical extrapolation of the shear using basic data coming from a lower altitude mast measurement is a cost and time-saving alternative. A theoretical extrapolation to higher hub heights without the information of the shear measured by LiDAR may lead to misinterpretations of the actual wind profile. Differences of diurnal variations comparing lower measurement heights with higher measurements at the site (Fig. 1) won t be detected. WTG Performance Measurement and AEP assessment with LiDAR With respect to power performance measurement and AEP assessment the rotor equivalent wind speed (Fig. 2) has become a focus of interest in the last years [6]. LiDAR will play an important role in this context as it enables measurements of the vertical profile from the lower to the higher rotor tips. Using the technology the uncertainties in an AEP estimation can be reduced significantly [13; 14]. Even though the current applicable IEC standard [9] does not yet account for the whole rotor swept area but only demands the measurement at hub height - the draft of the upcoming revision of the IEC [10] is already incorporating the specification of the rotor equivalent wind speed and will allow the use of wind LiDARs and SoDARs for the measurement. BBB already successfully performs power curve measurements by means of LiDAR technology (Fig. 3 and Fig. 4). Underperformance (in comparison to the guaranteed power curve) of turbines like shown in Fig. 4 can be detected very fast and easy not only for one but also for several turbines of one wind farm within a relatively

4 short period of time using the LiDAR technology. Hence, a fast response time for technical adjustments is possible. In order to acquire reliable data from a RSD it is crucial to regularly verify its performance and data output. Wind LiDARs are not calibrated like cup anemometers in wind tunnels but their performance is tested against a classical wind measurement mast erected in simple terrain which is equipped with cup anemometers and wind vanes (Fig. 5). The cup anemometers and wind vanes serve as the reference sensors and should be first class instrumentation, classified by the IEC [9]. The objectives of a LiDAR verification test are first and foremost to provide a proof of the measurement precision and secondly the estimation of deviations. Knowing this, the deduction of a correction factor and the determination of a corresponding uncertainty is feasible. Procedures and guidelines for LiDAR verification and associated analyses were published by the International Energy Agency [11] and by Gottschall et al. [12]. BBB has already performed many verification tests and as a result Windcube v2 LiDARs always showed very good accordance with classical first class anemometers (Fig. 6). This proofs its suitability for the application in the field of wind energy assessments. Establishing LiDAR measurements in Brazil In Germany, LiDAR technology is already widely spread and accepted by the relevant stakeholders and institutions [7]. In the up-coming markets like eg. Brazil this is not yet the case. In Brazil, in accordance with EPE guidelines [13], 24 months of wind measurement are mandatory. But LiDAR measurements are not yet allowed as standalone wind measurement application for the sale of wind and energy certificates at the public energy auctions. But also there, LiDAR is already used for the sharpening of energy yield prognoses and for the prospection of new areas and it will obtain an ever more important role in the future. Because particularly on those markets that have an auction system the pressure to reduce project uncertainties is steadily growing. Acting since 2011 in Brazil, BBB itself has recently opened up a branch and local office. Like the German parent company, BBB Energias Renováveis Ltda. offers a wide scope of engineering services and technical due diligence. Afonso Pacheco, who is experienced in the Brazilian wind energy market, is the general manager of BBB s affiliate. Knowing the situation in Brazil, Pacheco clearly sees the need for more reliable studies on the wind situation and consequently for more sophisticated measurement campaigns. For the promotion of Remote Sensing Technology in Brazil, BBB and the University São Paulo (USP) are nowadays jointly implementing a RSD test site which is also open for scientific research [14]. It is part of the University s efforts to build up a wind energy research cluster at the Institute of Energy and Environment where students are trained to meet the demands of the Brazilian wind industry. Thanks to the Brazilian - German cooperation, students are now already investigating the application of LiDAR technology. With their concept for the implementation of a test site for RSD in Brazil BBB qualified itself for the dena Renewable Energy Solutions Programme, which is coordinated by Deutsche Energie-Agentur (dena) - the German Energy Agency. It aims at promoting knowledge and technology transfer within the initiative renewables Made in Germany by granting financial support on behalf of the German Federal Ministry for Economic Affairs and Energy (BMWi). BBB s cooperation with the most influential University in Brazil lays a promising basis for the spreading of knowledge about the advantages of LiDAR technology in Brazil and other Latin American wind markets.

5 Tables and Figures Tab. 1: Reduction of uncertainty and improvement of IRR and bankability through LiDAR application and relocation in complex terrain for a planned hub height at 140m Number of turbines 10 Rated Power Wind farm 25MW Investment 49,350,000 Equity ratio 25% Equity 12,337,500 Scenario Only met mast (100 m) 12 months LiDAR next to mast 15 (+ 3 months) Second LiDAR at other position within wind farm area 21 (+ 2 x 3 months) Analyses vertical cross prediction of the model vertical cross prediction of the model and vertical extrapolation to hub height vertical and horizontal cross prediction as well as vertical extrapolation Total uncertainty Energy prognosis P % 14.1% 11.0% 100% 105.7% 105.8% IRR (P50) 14.7% 18.1% 18.2% Energy prognosis P % 95.6% 98.0% IRR (P75) 7.8% 12.0% 13.5% Sum of CF for operating phase 14,025,551 22,055,114 24,810,944

6 Fig. 1: Diurnal course of wind speeds for heights between 40 and 200 m above ground level Fig. 2: Rotor equivalent wind speed ? Height above ground level in m Rotor equivalent wind speed and energy Eeq = Espot Share of energy on swept rotor area in MWh x m² per 5m Segment

7 Fig. 3: LiDAR measurement for turbine performance testing Fig. 4: Measured (box plots) versus guaranteed power curve (green line) Turbine power / nominal power in % Windspeed in m/s

8 Fig. 5: mast Two LiDAR devices (within trailers) verified at BBB verification site in Germany against a wind met Fig. 6: Wind speed of a LiDAR (ordinate) versus wind speed of the reference mast (abscissa). Ordinary least square (OLS) fit based on the bin means.

9 Bibliography [1] E. Osler, 10 myths about wind LiDAR technology debunked, Leosphere, [2] The UpWind special issue, Wind Energy, vol. 15, no. 1, [3] N. Fichaux, J. Beurskens, P. H. Jensen, and J. Wilkes, Design limits and solutions for very large wind turbines, [4] Technical Guidelines for Wind Turbines - Part 6: Determination of Wind Potential and Energy Yield, Revision 9. Fördergesellschaft Windenergie und andere Erneuerbare Energien - FGW, pp. 1 52, [5] Use of remote sensing for wind energy assessments, no. April. Det Norske Veritas, [6] R. Wagner, M. Courtney, J. Gottschall, and P. Lindelöw-Marsden, Accounting for the speed shear in wind turbine power performance measurement, Wind Energy, vol. 14, no. 8, pp , [7] E. Dupont, Y. Lefranc, L. Soulier, and D. Koulibaly, Detailed analysis of uncertainty reduction on power curve determination using lidar measurements, in Proceeding of EWEA2 012, 2012, no. April, pp [8] L. Simmons, M. Quick, A. Marsh, and S. George, Power Performance Measurements Using Remote Sensing, in AWEA Windpower Conference & Exhibition, [9] IEC Ed.1: Wind turbines - Part 12-1: Power performance measurements of electricity producing wind turbines. IEC, p. 92, [10] Draft edition 2: IEC Wind turbines Part 12-1 : Power performance measurements of electricity producing wind turbines, Ed. 2., no. Cd. IEC, [11] A. Clifton, D. Elliott, and M. Courtney, Eds., Ground-based vertically-profiling remote sensing for wind resource assessment, 1st ed., vol. 15, no. January. iea wind, [12] J. Gottschall, M. S. Courtney, R. Wagner, H. E. Jørgensen, and I. Antoniou, Lidar profilers in the context of wind energy a verification procedure for traceable measurements, Wind Energy, vol. 15, no. 1, pp , [13] Instruções para Solicitação de Cadastramento e Habilitação Técnica com vistas à participação nos Leilões de Energia Elétrica, vol. r12. Empresa de Pesquisa Energética - EPE, Brasilia, pp. 1 38, [14] Projeto de Cooperação científica IEE/USP e BBB: "Remote Sensing Test and Verification Site - dena Renewable Energy Solutions Project". homepage:

10 Background information This project is part of the worldwide dena Renewable Energy Solutions Programme coordinated by Deutsche Energie-Agentur (dena) - the German Energy Agency - and co-financed by the German Federal Ministry for Economic Affairs and Energy (BMWi) within the initiative renewables Made in Germany. Deutsche Energie-Agentur (dena) The Deutsche Energie-Agentur (dena) - the German Energy Agency - is Germany's centre of expertise for energy efficiency, renewable energy sources and intelligent energy systems. dena's aim is to ensure that energy is used in both a national and international context as efficiently, safely and economically as possible with the least possible impact on climate. dena is working with stakeholders from the worlds of politics and business and from society at large to achieve this aim. Shareholders in dena are the Federal Republic of Germany, KfW Bankengruppe, Allianz SE, Deutsche Bank AG and DZ BANK AG. renewables Made in Germany Initiative Since 2002 the German government has been closely involved in supporting the global dissemination and transfer of technologies for renewable energies, under the brand renewables - Made in Germany. The responsible authority, the Federal Ministry for Economic Affairs and Energy, is thus making a significant contribution to international climate protection while promoting the worldwide acceptance and use of renewable energies. dena Renewable Energy Solutions Programme (dena RES Programme) The dena RES Programme was developed by the Deutsche Energie-Agentur (dena) the German Energy Agency. This programme, co-financed by the Federal Ministry for Economic Affairs and Energy within the initiative renewables Made in Germany, supports renewable energy companies entering new markets. Within the framework of the programme reference and demonstration projects are installed nearby designated institutions in different countries around the world. The installation is accompanied by comprehensive marketing and training programmes. These projects impressively present high-quality renewable energy technology. BBB Umwelttechnik GmbH BBB is one of Germany s top-ranking technical consultancies in the wind energy business, having a significant track-record of specialized engineering services provided in the field of project development. BBB s technical expertise spreads over all phases of a project development process. It offers a wide range of expert reports and other planning and engineering services, but also handles the implementation of entire projects on behalf of its customers. BBB elaborates bankable wind reports according to international standards and performs high quality wind measurements (met mast or LIDAR). BBB prepares analysis of extreme winds and effective turbulence intensities. Following its own strict demand for high quality engineering, BBB has acquired accreditations not only for the elaboration of wind yield assessments but also for wind measurements (DIN EN ISO/IEC 17025:2005). Last but not least, BBB as an independent consultancy is the ideal partner for technical Due Diligence services with a proven expertise in assessing major onshore and offshore projects.

11 Herausgegeben von / Edited by BBB Umwelttechnik GmbH Munscheidstr. 14; Gelsenkirchen info@bbb-umwelt.de Pressekontakt / Press Contact Markus Rieger / BBB Umwelttechnik GmbH Tel: m.rieger@bbb-umwelt.de