Paul Slangen Student identification number 1143565 Prefeasibility Study on Askjelldalsvatn Power Plant MSc. Thesis report Bergen, 25 February 2008 Delft University of Technology Faculty of Civil Engineering and Geosciences Section of Hydraulic Engineering In association with Bergenshalvøens Kommunale Kraftselskap Examination committee Prof. drs. ir. J.K. Vrijling (TU Delft) ir.J. van Duivendijk (TU Delft) ir. R.J. Labeur (TU Delft) Supervisor J. Matre (BKK Rådgiving) Paul Slangen MSc. Thesis Prefeasibility Study on Askjelldalsvatn Power Plant PREFACE This report is the result of a study performed by the author for his graduation thesis for the Master of Science title from Delft University of Technology, Faculty of Civil Engineering, for the Section of Hydraulic Engineering. The study is performed in association with the power company Bergenshalvøens Kommunale Kraftselskap (BKK) in Bergen, Norway. The author has investigated the feasibility of constructing a new power plant within an existing power scheme. This report presents the process and findings of this study. Decision makers are encouraged to read not only the summary and conclusions but also sections 1.1 and 9.4 for a better understanding of the selected solution. For readers who are already familiar with hydropower in Norway and the project area the chapters 5, 9, 10 and 11 will be of main interest. Chapter 8 and sections 10.2 and 10.3 contain the necessary information for an in-depth economic analysis of the project. Readers who are interested in the background for the design, the results and the process are welcome to read the complete report. My thanks go out to Jostein Matre for the opportunity he has given me to write my thesis study with BKK and for his work as supervisor of the project. I would like to express my gratitude to Han Vrijling, professor of the Section of Hydraulic Engineering, for his willingness to support this thesis work abroad and for his valuable comments. I would also like to thank Hans van Duivendijk and Robert-Jan Labeur who have supervised and valuably criticised the thesis work from their positions at TU Delft. Many thanks also go out to everybody of BKK Rådgiving for their help in any way, early lunch, wise advice and just good company. Finally I would like to thank my parents, my sister and Ina for their great support during the last six months. Bergen, February 25 2008 Paul Slangen i Paul Slangen MSc. Thesis Prefeasibility Study on Askjelldalsvatn Power Plant EXECUTIVE SUMMARY Bergenshalvøens Kommunale Kraftselskap (BKK) is the owner of the Evanger hydropower scheme and has requested to investigate the feasibility of a new power plant in this scheme. The objective of this study is to identify the technical and economical feasibility of a hydro power plant that utilizes the water flow between Holskardvatn and Askjelldalsvatn. A combined pump turbine plant with an installed capacity of 8 MW is found to be the optimal feasible solution. The net present value and construction costs are estimated as 46.2 MNOK and 98.7 MNOK respectively. The pumping up of 50 Mm3 yearly from Askjelldalsvatn to Holskardvatn will give a better balance in the system and lead to a large shift from summer to winter production in the Evanger plant. The free power market in Norway results in high energy prices in winter. The precipitation is then small and the energy demand is large as a result of the cold. In summer the runoff is high and with a low energy demand, the price is low. This difference in price and the topography in Norway make it beneficial to store water in reservoirs in summer and utilize it for energy production in winter. The main power plant in the Evanger scheme is the Evanger power plant, with a head of 770m. The intake reservoir for this plant is the relatively small Askjelldalsvatn and apart from the winter months the water level is at the highest regulated water of 805 m.a.s.l.. Holskardvatn is a large reservoir above Askjelldalsvatn, where water is stored in summer. The water is transferred through a tunnel system to Askjelldalsvatn in winter to ensure maximum production in the Evanger plant. The available head between these reservoirs varies from 25m to 70m. In the identified range of flows both Francis and Kaplan turbines can be selected. The turbine characteristics are essential for the design, because of the widely varying available head. Several experience values for design have been found in literature and are presented. The main requirement for the new power plant is that it may not become a bottleneck for the Evanger plant. To fulfil this requirement it is decided to keep the existing gate system, beside the new plant. To find the most economic design of the power plant, two starting points of design are used: minimum costs and maximum value. The main design variables are the outlet level, the installed capacity and a pumping mode. For all alternatives one unit is selected and a Francis turbine preferred over a Kaplan turbine, because it is cheaper. For all alternatives drawings, a Bill of Quantities and an energy estimate have been provided. The latter two have been used as input for the economic analysis. Three basically different preliminary designs are proposed, based on the two starting points for the design: - Alternative I aims to minimize the costs. The outlet level at the highest regulated water level in Askjelldalsvatn makes a short and cheap alignment possible. However, only 40% of the available water can be utilized for energy production for this alternative, the rest needs to be bypassed because the available head is outside the range of the turbine. - Alternative II is designed as a compromise between maximum energy and minimum construction costs. The water is bypassed around the existing gates, through the power plant and into the existing lower diversion tunnel with an outlet at 783 m.a.s.l.. The large costs for the underground works however result in a small profit for this alternative. Installing a combined pump turbine in this design shows very good results. 50 Mm3 water is pumped up in summer and almost 65 ii Paul Slangen MSc. Thesis Prefeasibility Study on Askjelldalsvatn Power Plant GWh of energy production shifts from summer to winter, mainly in the Evanger plant. This shift results in additional yearly benefits of approximately 2 MNOK. - Alternative III is designed to maximize the potential energy and the outlet is placed at 770 m.a.s.l. This makes it possible to utilize almost all available water for energy production. This design showed similar economic results as the previous alternative (also for the combined pump turbine), but with both higher costs and value. The combined pump turbine solution is studied in more detail. The optimization process focuses on the outlet level and installed capacity. Both combined pump turbines from the preliminary design phase, plus a design with a lower outlet at 760 m.a.s.l. have been optimized for the installed capacity. An outlet level of 768 m.a.s.l. with an installed capacity of 8 MW for the pump turbine is an optimum solution. With the new plant, the water level in Askjelldalsvatn does not go below this water level as a part of the snow melt can be pumped up to Holskardvatn and thus does not need to be stored in Askjelldalsvatn. The selected installed capacity is the highest installed capacity that is fully utilized; one additional MW would only be used incidentally and is therefore not found to be beneficial. It is recommended to apply for a license for the plant as soon as a study has been performed to estimate the costs for the transmission system in more detail. For a more detail design of the plant it is also necessary to acquire more detailed topographic maps and more specific information on turbines from turbine manufacturers iii Paul Slangen MSc. Thesis Prefeasibility Study on Askjelldalsvatn Power Plant TABLE OF CONTENTS Preface ................................................................................................................ i Executive Summary.............................................................................................. ii Table of Contents ................................................................................................ iv List of Figures and Tables ..................................................................................... vi Glossary of abbreviations, definitions and units .......................................................vii Introduction ....................................................................................................... ix 1. Design Process .............................................................................................. 1 1.1. General Approach.................................................................................... 1 1.2. Methodology........................................................................................... 2 2. Hydropower in Norway ................................................................................... 3 2.1. Hydropower ........................................................................................... 3 2.2. Topography............................................................................................ 4 2.3. Climate.................................................................................................. 5 2.4. Hydrology .............................................................................................. 5 2.5. Power Market in Norway..........................................................................