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Research SBN 978-3-98

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129

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130

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131

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ne power ams show ercentage ed for the kW up to 6.5 % for

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ut 72 % to 00 kW) is

132 Naulin & Albers

higher and the surface roughness of the terrain affects the wind to a lesser extent. For the catchment area of Steertloch the total required pump capacity was estimated to about 600 kW. This equates a possible wind energy supply from approx. 75 % which represents 240 MWh. Moreover, there is a remaining energy production of 2,400 MWh by the WEP.

Alternative 2: reservoir with wind-driven pump As the second alternative the feasibility of a reservoir with wind-driven pumps was examined. It is noted that a mechanical power transfer between the wind turbine and the pumps is not feasible since mechanical pumping systems only achieve a maximum of 10 kW as rated capacity (Gasch & Twele 2005) which falls below the value of the required pump capacity of 600 kW. With an electrical power transfer the alternative 2b corresponds to alternative 1 including an additional reservoir. By means of the reservoir there is the advantage of adopting the operation of the pumps. Since the water can be stored in the reservoir the pumping times are adjustable to periods with sufficient wind energy supply. For the existing reservoir of the sluice Steertloch the storage volume was calculated by an elevation model covering the data of the bathymetry and the terrain with the software ESRI ArcView. Between the water levels -1.5 mNN and 0.0 mNN the storage volume was estimated to 425,000 m³. With a design discharge of 12.6 m³/s the storage time amounts 9.3 hours. This alternative offers the use of control and feedback control systems where the operation of the pumps can be adjusted to the wind energy supply. Therefore the wind energy supply is estimated as a greater value than in alternative 1, viz. greater than 75 %.

Alternative 3: cascading drainage system using WEP and hydro power The third alternative is composed of a cascading drainage system using wind energy and hydro power. Therefore at first the water is pumped by a WEP into a high lying polder. From the higher polder the water can be drained by gravity and at the same time hydro power can be gained by powering a generator with the discharge of the water. As a type of generator, pumps as turbines can be applied since the boundary conditions of a changing flow rate and a low head have to be considered. Compared to the wind energy production with a total of 2,600 MWh the production of hydro power with 240 MWh is rather low.

4 Results Besides the review of technical feasibility the alternatives were evaluated on the basis of calculation of their economic efficiency. The costs have been estimated considering the investment and operating costs as well as the tariffs for wind energy and hydro power due to the Renewable Energy Sources Act (Erneuerbare-Energien-Gesetz/ EEG). In order to give some example of the expanses the investment costs of a WEP comparable to the model Enercon E-48 (800 kW) amount to 1.2 million euro. The investment costs of the pumping system were neglected since these values are the same for each alternative. The operating costs mainly consist of energy costs which average up to 310,000 euro/year with an electricity tariff of 15 cent/kWh for a conventional pumping station. For wind energy the tariffs following EEG 2009 are summed up to 160,000 till 170,000 euro/year for a period of 20 years. The tariffs of hydro power result in a maximum of 30,000 euro/year. Table 1 shows the results in terms of the annuities for the different pump capacities of 220 kW and 660 kW. It can be seen that alternative 3 with the cascading drainage system using hydro power is not economic. By contrast the alternatives using energy of a WEP for a pumping system are profitable. In comparison with a conventional pumping system annual costs of up to 47,000 euro/year can be saved.

Feasibility Study for Optimisation of Land Drainage 133

Table 1: Results of evaluation of economic efficiency in terms of annuities considering investment, operating coast as well as tariffs for wind energy and hydro power after EEG (2009) for a period of 20 years

Pump capacity Alternative 0: Conventional

pumping station

Alternative 1: Pumping station

with WEP

Alternative 2: Reservoir with WEP

pumping system

Alternative 3: Cascading drainage using hydro power

220 kW -16,000 euro/year +20,000 euro/year > +20,000 euro/year -337,000 euro/year 660 kW -48,000 euro/year -1,000 euro/year < -1,000 euro/year -338,000 euro/year

5 Summary Wind energy was identified as being highly relevant for drainage methods, therefore analyses of the energy demand of a pumping station and the supply of wind energy were carried out over a period of three years in the coastal regions of the North Sea in Dithmarschen. It was found that there is a relation between the investigated quantities and as a result it could be shown that the energy demand of a coastal pumping station could be predominantly supplied by a wind energy plant. Three alternatives to use wind and/ or hydro power were reviewed for feasibility and evaluated on the basis of calculations of economic efficiency. The analysis indicates that electric wind pumping systems are highly appropriate for use in sustainable drainage systems and from the economic point of view the annual costs can be reduced by a factor of 48 compared to conventional pumping systems.

References DVR-Bremen (2008): Bremischer Deichverband am rechten Weserufer. Personal communication with Mr.

Döscher and Mr. Dülge at May 30th 2008. Gasch, R. & J. Twele (2005): Windkraftanlagen,. Teubner Verlag, Wiesbaden, 540 S. IPAT - Internationale Projektgruppe für angepasste Technologien (1989): Der Einsatz von Windpumpsystemen

zur Be- und Entwässerung. Fachbereich Internationale Agrarentwicklung der TU Berlin. Berlin, 219 S. LKSH - Landwirtschaftskammer Schleswig-Holstein (2008): Windenergie XX Praxisergebnisse 2007,, 98 S. Maniak, U., A. Weihrauch & G. Riedel (2005): Die wasserwirtschaftliche Situation in der Unterwesermarsch

unter der Einwirkung der Klimaänderung. In: Schuchardt, B.& M. Schirmer (Hrsg.): Klimawandel und Küste, Die Zukunft der Unterweserregion. Springer Verlag, Berlin und Heidelberg, S. 79–100.

Acknowledgement The work has been carried out as part of the first authors diploma thesis at the Hamburg University of Technology in collaboration with the water board Deich- und Hauptsielverband Dithmarschen. The supervision and provision of data by the latter is gratefully acknowledged. Moreover, special thanks for additional support goes to DVR Bremen, Enercon, Köster Heide, KSB, BSU and FHTW.

Address Marie Naulin Technische Universität Braunschweig, Leichtweiss-Institute for Hydraulic Engineering and Water Resources Beethovenstrasse 51 a 38106 Braunschweig, Germany

m.naulin@tu-bs.de