Title: Hydro Energy for Maurice Ile Durable

Transcription

1 Title: Hydro Energy for Maurice Ile Durable Authors: Girish Kumar Beeharry 1 *, Mohinsha Sookdeb 2, Vimi Dookhun 2 Affiliation: 1 Physics Department, University of Mauritius 2 Chemical & Environmental Engineering Department, University of Mauritius gkb@uom.ac.mu Abstract This paper considers the present status and the future of hydro energy potential in Mauritius. The focus is on the potential itself rather than on the applications. This source of sustainable energy, which is not a major component of the local energy mix, is nonetheless a reliable one. 1. Introduction Mauritius has 25 major river basins and the largest are the Grand River South East and the Grand River North West. Most rivers are perennial, originating from the Central Plateau. Discharge to the sea is estimated to be.5 km 3 /year. Mauritius has five main aquifers. Total renewable water resources are estimated at km 3 /year. Total exploitable water resources are estimated at 1.83 km 3 /year. Total dam capacity is 93 million m 3. There are five main storage reservoirs (Mare aux Vacoas, La Ferme, Mare Longue, La Nicoliere, Piton du Milieu) and one impounding rockfill dam (Midlands Dam). Minor reservoirs for hydropower are Tamarin, Eau Bleue and Diamamouve and there are two infield minor storage reservoirs at Valetta and Dagotière, which regulate water for irrigation.[3.1] 2. Technology Hydroelectricity, also known as hydro, is a well-developed renewable technology that has been around for more than a century. It uses the energy of flowing water to spin a turbine connected to a generator that produces electricity. The amount of electricity generated depends on the volume of water and the height of the water above the turbine. Hydroelectricity does not actually use water: all the water is returned to the river. Large hydroelectric power stations need dams to store the water needed to produce the electricity.

2 Figure 3.1: Water resources in Mauritius and Rodrigues [3.]

3 These dams are often built for irrigation or drinking water, and the power station is included in the project to ensure maximum value is extracted from the water. Large hydroelectricity stations form a critical part of the electricity grid as a highly predictable and controllable power source. Hydro can provide both base load and peak load electricity; and hydro generators can start up and supply maximum power within 9 seconds. Smaller hydro power stations, called mini or micro may not need dams but rely on naturally flowing water such as streams. These also provide a good source of base load power and are often used as stand-alone systems not connected to the main electricity grid. [3.2] Water, Mm Water Balance Year Rainfall Surface runoff Evapotranspiration Net recharge to groundwater Figure 3.2: Water Balance for Mauritius Volume of water used for Hydropower Generation Mauritius is well endowed as regards natural water input in the form of rainfall. However, one can gather from Figure 3.1 that over a 9 year period, from 1999 to 27, only some 1% of rainfall water is retained as ground water. Furthermore, water runoff constitutes 6% of the rainfall. It seems that more effort in water collection can be made at not only national level in large reservoirs but also in inhabited and farmed areas. This can enhance the possibility of having mini hydro stations. Only 2% of water resources are used for power generation, see Figure 3.2.

4 Figure 3.3: Water Utilization Volume of water used by CEB for Hydropower Generation 1 Volume of water, Mm Year Champagne Ferney Tamarind Falls Le Val Reduit Cascade Cecile Magenta La Ferme Source: CSO Figure 3.4: Volume of water used by CEB for Hydropower Generation-Break down by station

5 4 Total volume of water used by CEB for Hydropower Generation Volume of water, Mm Year Figure 3.5: Total Volume of water used by CEB for Hydropower Generation-All stations Hydropower is one of the oldest sources of energy in Mauritius, dating from There are at present 8 hydro power plants in the country, with electricity output ranging from 94KW to 3, KW. The annual mean production of electricity for all the 8 hydro power stations is approximately 1 Million KWh. This represents merely 5% of the total electricity production of the island. Worldwide, hydropower is the leading source of non-polluting energy and it provides more than 17% of all renewable electricity generated. Country wise large variations are seen: 5% of the electricity produced in New Zealand and over 99% of the electricity produced in Norway come from hydropower. However, in Mauritius, tapping the technically feasible hydropower potential is a challenge as the whole policy of water collection, distribution and supply needs to be revisited.: 6% of rainfall water is lost as surface runoff and an estimated 4% of water distributed in the pipelines is lost. In fact that Mauritius is heading towards the water stress condition despite having a rather abundant average rainfall supply of 37 Mm 3! Hydro power production is related to the amount of mean annual rainfall. So, in case the country experiences a drought, the electricity output will be greatly affected. Figure 3.5 shows how the mean annual rainfall influences the share of electricity production from water [1.5].

6 Variation in HydroPower Production with Mean Annual rainfall 6. 2,5 Share of Hydro Electricity Production, % , 1,5 1, 5 Mean Annual rainfall, mm Year Share of Hydro in electricity production Mean annual rainfall,mm Figure 3.6: Mean Annual Rainfall Average Yearly Producton, GWh Average Yearly Producton, GWh Ferney Le Val Champagne Tamarind Falls Cascade Cecile La Ferme Reduit Magenta Figure 3.7: Average yearly production by station

7 3.2 Methodology We have analysed the potential of hydroelectricity for each station by calculating the power production, using a simple model and various assumptions on efficiency and days of operation. A simple formula for approximating electric power production at a hydroelectric plant is: P = ehrρg where P is Power in kilowatts, h is height in meters, r is flow rate in cubic meters per second, ρ is the density of water, g is acceleration due to gravity of 9.8 m/s 2, and e is a coefficient of efficiency ranging from to 1. Efficiency is often higher with larger and more modern turbines. Annual electric energy production depends on the available water supply. In some installations the water flow rate can vary by a factor of 1:1 over the course of a year. Power station Champagne Ferney Tamarind Falls Le Val Reduit Cascade Cecile Magenta La Ferme Year of operation Dam Capacity, m 3 4.3E E E+6 4.1E Diameter of pipe, m Radius of pipe, m Gross Head, m Flow rate at Full Load/unit, m3/s Average Yearly Producton, GWh Results and Discussion We have used the above formula to estimate the potential, Calculated Average Yearly Production(CAYP) of the hydro stations for different efficiencies and periods of operation. In Figures 3.8 and 3.9 below, we show the results of the analysis.

8 GWh Comparision of Major Hydro Stations Champagne Ferney Tamarind Falls Stations Average Yearly Producton, GWh t=27d) t=18d) t=18d) CAYP, GWh, (e=5%; t=9d) t=9d) CAYP, GWh, (e=5%; t=27d) Figure 3.8: Comparison of actual and computed production for major hydro stations The Champagne station has a good potential for production provided it can be made operational for a significantly longer period every year. As seen in the modeled estimate, operation at an efficiency of 75% and during 18 days can reap 185 Gwh, about 4.8 times its present output. This can be made possible if an adequate supply of water is available from nearby reservoirs. This fact is generally true of the other stations but with less potential output. Further development hinges on the extension of the Midlands dam to a much larger capacity. The future La Nicolière hydro power plant is to produce 2 GWh annually.

9 12 Comparison of Minor Hydro Power Stations 1 8 GWh Le Val Reduit Cascade Cecile Magenta La Ferme Stations Average Yearly Producton, GWh t=27d) t=18d) t=18d) CAYP, GWh, (e=5%; t=9d) t=9d) CAYP, GWh, (e=5%; t=27d) Figure 3.9: Comparison of actual and computed production for minor hydro stations 4.1 Strengths 1. The main strength is that Mauritius has an adequate rainfall. 2. It is a small (5%) but dependable energy source. It is much more reliable than wind or solar power. 3. It has historical significance as it was the first source of commercial distributed electricity. 4. The cost of running is comparatively low. 5. The waste or pollution produced is minimal. 6. It can in principle help to cope with peaks in demand. 7. Hydro stations can increase to full power quickly, unlike other power stations. 8. Electricity can be generated constantly, provided there is sufficient water in the dam. 4.2 Weaknesses 1. Using the present set up, hydro power has already reached a capacity of 9% of the potential. 2. Geographically the topography of Mauritius is rather flat compared to say Reunion Island. 3. Investment in dam building is very costly and, with limited resources, it is difficult to expand further except as an appendage to new dam projects. Costs can be shared with irrigation projects and other water users. 4. The upstream environmental impact of a large dam on any resident population, the flora and the

10 fauna that used to live there is significant. This situation was witnessed in the case of the Midlands dam. 5. Any future choice of a potentially good site can be negated by its impact on residents and the environment. 6. It is very climate dependent. 7. Downstream water quality and quantity can be affected, thus impacting on the ecosystem. [3.3] 4.3 Opportunities 1. Support from International Agencies for implementation of renewable energy Sources 4.4 Threats 1. Budget Constraints 2. Environmental issues 5. Conclusion 5.1 Short Term Recommendations Determine the gross hydropower potential of Mauritius through calculations and modeling with software like WaterGap The gross hydropower potential GP is defined as GP = m g h m: Mass of runoff g: Gravitational acceleration h: Height (elevation above sea level) The gross hydro power potential can help to assess the country s future hydro power situation. This important but delicate and demanding work can be conducted at desktop level. Nonetheless, its intricate difficulty is not intractable. 5.2 Medium Term Recommendation

11 1. Do an in-depth study of the hydro station to find ways to optimize hydro power generation- through more efficient systems. 2. Study the possibility of increasing the capacity of the Midlands dam. 3. Use a local computational climate model to estimate the future hydro potential using different global warming scenarios. 5.3 Long Term Recommendations 1. Study the possibility of increasing the water storage by the judicious location of new reservoirs and dams 6. Acknowledgment The authors express their sincere thanks the Ministry of Renewable energy and Public Utilities for supporting this project. 7. Bibliography CSO (29 Mauritius in Figures. Retrieved 22 March 29 from