WIND ENERGY UNDER THE ASPECT OF SUSTAINABILITY. Authors. Hermann-Josef Wagner, Rodoula Tryfonidou Institute for Energy, University of Bochum.

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1 WIND ENERGY UNDER THE ASPECT OF SUSTAINABILITY Authors Hermann-Josef Wagner, Rodoula Tryfonidou Institute for Energy, University of Bochum Abstract Beside water and biomass, wind energy is the most favourable renewable energy technology worldwide. There is an enforced market development of onshore and also offshore wind energy facilities worldwide. The construction of wind farms is material-intensive and needs a big amount of fossil energy. Connected with the energy consumption are emissions of green house gases. From these aspects arises the question: Is the use of wind energy sustainable? To answer the question the international methodological approach of Life Cycle Assessment will be used. Life Cycle Assessment (LCA) is an instrument to quantify all impacts of the entire energy supply chain. To obtain the Cumulative Energy Demand (CED) for production, for instance, of a power plant, the whole facility has to be split up into components, subcomponents and their respective materials. Using this material balance with specific data for material, energy resources and emissions it is possible to calculate the CED. For final evaluation of the energy systems Energy Payback Time (EPT) as relationship of harvested energy (valued as primary energy) and total Cumulative Energy Demand has been used to decide if market development of wind energy is sustainable enough or not. This paper will present and discuss the results of wind turbines with different rated power output. For calculating the yearly energy output two sites have been selected: onshore (coastal) and offshore. An average size wind turbine of 1.5 MW, has been chosen to be considered in case of onshore use. Beside that a multi megawatt wind turbine of 5 MW offshore located, is considered. The results of this study show that -surveying the life cycle of a modern wind turbine-, much more primary energy can be harvested during the operational phase, than it is actually needed in the constructing phase. To advise politics in term of market introduction of renewable energies it is absolutely necessary to do such kind of investigations. Lead Author Hermann-Josef Wagner Prof. Dr.-Ing. Institute for Energy, University of Bochum Universitaetsstr. 150, IB 4/125, Bochum, Germany Phone: +49 (0) / Fax: +49 (0) / lee@lee.rub.de

2 1. Sustainability indicators To assess energy systems with regard to their sustainability and to yield well-founded conclusions for decision making processes, quantitative indicators are needed. Consistent with the sustainable approach of the depletion of non renewable resources, their use for conversion processes and resulting impacts on the environment plays a major role for energy systems. According to the Life Cycle Approach, an appropriate indicator system should comprise all steps of a system s life cycle: production, operational and disposal processes. It can be applied to evaluate energy systems based on fossil and nuclear fuel chains as well as renewable energy sources. With regard to these aspects, two indicators are presented in this paper: the Cumulative Energy Demand (CED) and the Energy Payback Time (EPT). 2. Methodology The CED methodology has been applied in various studies in the context of Life Cycle Inventory (LCI) [1] [2]. In general, the CED states the entire energy demand, valued as primary energy, which arises in connection with production, use and disposal of an economic good: CED Total = CED Production + CED Utilisation + CED Disposal (1) Due to the CEDs of selected renewable energy conversion systems, a choice might be made between different technologies with an ultimate aim of reduction of load on energy resources. Thus, the CED is both an economic and environmental indicator representing the magnitude of resource depletion, resource use and connected environmental impacts, e. g. climate effects, acidification, eutrophication, tropospheric ozone formation potential. With regard to ISO (compare [3]), the methodology of CED corresponds with the Life Cycle Assessment (LCA), as long as the accounting of material balances is seen as part of inventory analyses. Furthermore the calculation of CED represents a rough form of impact assessment. Consequently, CED can be seen as a streamlined LCA [4]. To obtain the CED Production, for instance, of a power plant, the whole facility has to be split up into components, sub-components, intermediates and their respective materials. Using this material balance with specific data for material and energy resources it is possible to calculate the CED. The Energy Payback Time (EPT) of a system is the time required to recover the total energy investment made. It shows the period of operation a system needs in order to substitute its physical net energy generation for the quantity of primary energy which had to be spent on its production, operation and disposal. The definition of the Energy Payback Time (Figure 1) as the relationship of produced energy to total CED, can be helpful for the final evaluation of the energy systems.

3 Gained or substituted Primary energy equivalent EPT operational phase Time of earning disposal Primary energy demand (CED) for Production, Operation, Disposal construction phase Start of construction Start-up End of operating Figure 1: The scheme of Energy Payback Time (EPT) For calculating the yearly energy output a coastal site and an offshore site, 30 miles away from the coast, have been selected: As reference units two different wind turbines made in Germany have been chosen to be considered in this paper: an average sized wind turbine of 1.5 MW without gear unit in case of onshore use and a multi megawatt wind turbine of 5 MW with gear unit located offshore. 3. Wind turbine for onshore use Reference unit for the onshore case is a wind turbine produced by the company ENERCON GmbH, Aurich (called 'E-66') located at the German coast. The features of the E-66 are as follows: Table 1: System Details of wind turbine for onshore use Onshore wind turbine 'E-66' Peak Output: 1,5 MW Hub Height: 67 meter Rotor Blade Diameter: 66 meter Capacity Factor: ~ 29 % Av. Wind Speed at Hub Height: 7.3 m/s System Lifetime: 20 a Electrical Power Output: 4.1 GWh/a The most important assumptions used in this analysis are (see also [5]): All the components except the foundation are made at the production plant situated in northern Germany. The machinery is transported by truck to the site.

4 Maintenance of rotor blades (coating) is required again after 10 years. Other parts must be replaced, too. Credits for recyclable materials were not granted. 4. Multi-megawatt wind turbine for offshore use The reference unit for the offshore use is a prototype wind turbine of 5 MW produced by the company REpower Systems AG, Hamburg under the designation '5M'. The offshore site is located in the German Bight, 45 km to the north of Borkum Island and 150 km to the coast. The water depth varies from 20 to 30 m and the average wind speed at hub hight is up to 9.2 m/s. The features of the offshore wind turbine are as follows: Table 2: System Details of wind turbine for offshore use Offshore wind turbine '5M' Peak Output: 5 MW Hub Height: 90 meter Rotor Blade Diameter: 126 meter Foundation: Tripod Capacity Factor: ~ 50 % Av. Wind Speed at Hub Height: 9.2 m/s System Lifetime: 20 a Electrical Power Output: 17.5 GWh/a The most important assumptions used in this study are (see also [6]): All components except the rotor blades are produced in Germany and transported to the production plant situated in Northern Germany by truck. Transportation to the site and erection of the wind turbine are realised by special ships from the nearest port. Lifetime of the wind turbine is 20 years, while the lifetime of the tripod foundation is approximately 40 years. Therefore, the foundation has been taken into account only for 50 % of the CED calculation. Service travels are necessary three times a year; a general overhaul of the wind turbine (replacement of components) is made after ten years. Credits for recyclable materials were not granted. 5. Material and Energy Balance For finding the material and energy balances both wind turbines have been considered to be divided in four parts which are: Rotor blades Machinery Tower Foundation Energy consumption for service and maintenance and also for transportation, mounting and dismantling has been taken into account. Figure 2 and Figure 3 give the break-up of the CED for each wind turbine design.

5 The CED of the 'E-66' sums up to about 13,500 GJ. The most important component group, due to a high content of energyintensive materials (e. g. copper for the generator), is the machinery with a share of about 46%. The tower has also a big share of about 28%. The foundation holds 11% and rotor blades hold about 8%. For service and maintenance only 1% of the total CED is needed while transportation, mounting and dismantling contribute about 6%. CED [GJ] 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0,000 Rotor Blades Maschinery Tower Foundation Service and Maintenance Transportation/ Mounting/Dismantling Figure 2: CED of the onshore wind turbine 'E-66' The CED of the offshore wind turbine '5M' sums up to about 85,000 GJ whereas the tripod foundation made of steel has the biggest share of about 31%. In contrast to the 1.5 MW wind turbine the machinery only has a share of about 20%. The tower contributes about 15% while rotor blades hold a share of 7%. Service and Maintenance during the lifetime of the wind turbine contributes about 22 % to the total CED. The major share of maintenance goes in replacement of components (e. g. gear box). For transportation, mounting and dismantling only 5% are needed. CED [GJ] 90,000 80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000 0,000 Rotor Blades Tower Maschinery Foundation Service and Maintenance Transportation/ Mounting/Dismantling Figure 3: CED of the offshore wind turbine '5M'

6 5. Energy Payback Time To calculate the Energy Payback Time, the net harvest of energy has to be appraised. Using the installed load of the wind turbines and the expected capacity factor as given in Table 1 and Table 2, and considering the system efficiency factor, the net electrical power output can be found. Using the German average primary energy conversion factor of electricity of 0.33 the net harvest has been converted to equivalent primary energy. The Energy Payback Time for the 1.5 MW coastal Wind Turbine is about 4 months while the Energy Payback Time for the 5 MW offshore design is approx. 5 months. 6. Remarks and Conclusions Offshore projects require constructions of large dimensions which are associated with corresponding environmental impacts. The results of this study show that -surveying the life cycle of a modern wind turbine-, much more primary energy can be harvested during the operational phase, than is actually needed in the constructing phase. Due to the higher energy yield the Energy Payback Time of the 5 MW offshore wind turbine is lower than expected and lies not much higher than the EPT for coastal onshore facilities (Figure 4). Cumulative Energy Demand, Yearly Energy Output MW offshore design 1.5 MW coastal Yearly Energy Output (primary) [1000 GJ/a] CED [1000 GJ] By share of infrastructure Figure 4: Comparison of CED and Yearly Primary Energy Output However, some restrictions have to be made: In the context of this analysis it was not possible to determine the aspects of a back-up system needed for reasons of security of energy supply. This methodical aspect can be analysed in future studies. Regarding the calculation of Energy Payback Time, the results are related to the average wind velocity at the site. In case of onshore use a difference can be made between coastal, near coastal and inland locations. Depending on the site the Energy Payback Time for onshore wind turbines varies between 4 months (coastal) and 6 months (inland) [5]. Furthermore, the results in this paper are valid only for the reference systems. Sensitivity analysis shows that the results can differ in the range of 20% [5] [6]. The main focus lies on the ecological aspects of the energy conversion systems. Economical and social criteria are not discussed in this paper. According to the

7 sustainability approach, indicators such as electricity production costs, employment effects, specific use of land, air and water and energy supply related risks have been developed in a further study [7]. 6. References [1] Hagedorn G., 'Hidden energy in solar cells and power stations', Proceedings of 9th PV specialist conference, pp , 1989 [2] Heithoff J., Rehnelt J., Schwaiger K., Zell J., 'Ganzheitliche energetische Bilanzierung von Kohlekraftwerken', Brennstoff Wärme Kraft, 50, No.3, 1998, pp [3] ISO14040 International Standard, International Organisation for Standardization: Environmental management Life cycle assessment Principles and framework, Beuth-Verlag, Berlin, [4] Guerzenich D., Mathur J., Wagner H.J., Bansal N.K., 'Cumulated Energy Demand of Selected Renewable Energy Technologies', Int. J. Life Cycle Assessment, Vol.4, No.3, 1999, pp [5] Pick, E.; Wagner, H.-J., 'Beitrag zum kumulierten Energieaufwand ausgewählter Windenergiekonverter', Report of the Chair for Energy Systems and Economics, University of Bochum, 1998 [6] 'Lebenszyklusanalysen ausgewählter zukünftiger Stromerzeugungs-techniken', Informationsschrift der VDI-Gesellschaft Energietechnik, Düsseldorf, 2004 [7] Petrovic, T. J.; Wagner, H.-J. 'Nachhaltigkeit am Beispiel regenerativer Energiesysteme zur Stromerzeugung', Final Report, Chair for Energy Systems and Economics (LEE), University of Bochum, 2005 (in publication)