Hydropower in Mauritius: Holistic Optimisation for Sustainability30 May 2014
The potential of hydropower in Mauritius is widely acknowledged to have been almost fully tapped. However, qualitatively, there is the opportunity to use such potential to face peak power demand, enhance water storage and availability for domestic and other purposes. Khalil Elahee from the University of Mauritius believes that the optimal use of hydropower can serve towards the ultimate goal of achieving sustainability.
The Republic of Mauritius in the Indian Ocean is made up of several islands with an Exclusive Economic Zone of more than 2.3Mkm2. The island of Mauritius has a highest point above sea level of 828m whilst on the island of Rodrigues the corresponding point is 398m high. Other archipelagos and atolls (Agalega, St Brandon, Tromelin and Chagos ) are almost at sea-level.
With a population of 1.3M, the country has a very high population density of 617 inhabitants per km2, almost all living on the island of Mauritius with an area of 2040m2. The latter has about 50 rivers flowing to the sea from the 600m high Central Plateau. In 2012, Mauritius received 3001Mm3 of precipitation (rainfall). Only 10 % of the precipitation went as ground water recharge, while evapotranspiration and surface runoff accounted for 30% and 60% respectively. Total water utilisation was estimated at 800Mm3 in 2012, with hydropower constituting 27% (218Mm3 ). Around 85% of the total water utilisation was met by surface water and the remaining 15% by ground water. During 2012, the mean amount of rainfall recorded around the island of Mauritius was 1609mm.
Climate change impacts are likely to account for average temperature rises (an increase of 0.74°C when compared with the 1961-90 mean), an increase in the frequency of extreme weather events, heavy rains and storms. Mauritius normally has a mild tropical maritime climate where mean temperature is 24.7°C in summer and 20.4°C in winter. The relative humidity level is usually above 80%.
Over the period 2003 to 2013, total electricity consumption in Mauritius increased by more than 35%. In 2013, almost 80% of the grid electricity was derived from imported fossil fuels, mostly coal, compared with about 72% in 2003. Maximum peak power demand had been consistently higher during the summer by about 20% compared with the maximum peak power for the previous winter. In February 2013 a record peak of 439MW was attained. According to the Energy Observatory of Mauritius, this was due to the massive use of air-conditioners in the country.
Hydropower in Mauritius
The first time electricity produced in Mauritius was in 1899 from the Reduit Waterfall. A year later, the Atchia brothers set up an electricity company lighting the neighbouring area of Beau-Bassin/ Rose Hill as from 1906. When Mauritius achieved Independence in 1968, as much as 60% of its power was derived from renewable sources, mostly hydro. Since then, the share of hydro in the energy mix has decreased significantly representing today less than 3%. Figure 1 below shows the evolution of hydropower production from 2003 to 2012. The relationship between rainfall in the Central Plateau where most of the reservoirs are situated and hydropower is given in Figure 2. There is no strong correlation between the two latter quantities as a number of other parameters have a strong influence on hydropower output, like storage and demand. Also, hydropower has been used as an alternative to gas-turbines fuelled by kerosene during peak periods. However, as shown in Figure 3, the increase in hydropower has not always caused a drop in the power generated by kerosene.
Two privately run, small hydro plants, namely Riche en Eau (200kW) and Bois Cherie (100kW) are connected to the grid. A third one, of 100kW capacity, is used for local purposes at Britannia. A 350kW plant is also envisaged across the Bagatelle Dam currently under construction (14Mm3). The total effective capacity of hydropower today equals 55.8MW or 9% of the total for Mauritius. The cost of hydropower is between Rs0.50 (US$0.015) and Rs 1.00 (US$0.030) per kWh, at least ten times less than that of kerosene-powered gas turbines.
A proposal has been developed at the University of Mauritius to install a pumped hydro station at Champagne. During off-peak hours, grid electricity can be used to pump water to Sans Souci dam whilst during peak periods hydropower can thus be used instead of kerosene-powered gas turbines. A financial pre-feasibility study gives a payback of less than five years but this is subject to a number of technical considerations. In particular a sustainability assessment is needed on the possibility of construction a downstream reservoir after the turbines. The latter measure will also serve to collect some 8m3/sec of water currently drained into the sea after leaving the hydropower plant.
In 2003, the sole utility provider of the country, the Central Electricity Board (CEB), had identified a potential for pumped storage at Tamarind Fall, but no project was elaborated. Together, Champagne and Tamarind Falls can provide about 36MW of pumped storage which is a significant asset to handle peak power demand instead of kerosene power. Coupling the latter systems with wind or solar power generation and storage has been evoked in the context of small-islands but more research is needed before commercial feasibility can be envisaged.
In 2003, CEB reported that due to the diversion of water from Midland Dams to La Nicoliere reservoir, hydropower was reduced by 12GWh, that is some 15%. Evidence for this is not deducible from Figure 1 because other factors are involved like rainfall, storage and demand. This is, however, an issue requiring deeper investigation in the context of a thorough integrated survey of water supply and demand.
A major orientation in terms of power sector reform has occurred since 2005. Private participation has been encouraged in the generation of electricity. This orientation has been strengthened in the Integrated Electricity Plan of the CEB for 2013-22 with a confirmation of the practice of least-cost dispatch based on the marginal cost of generation. Moreover, since early 2014, legislation has been amended to allow the private sector to produce and sell electricity without going through the CEB. Such liberalisation of the power market may serve the cause of existing private-run small hydro facilities and open the way for even smaller independent hydropower producers for specific clients. Under an existing feed-in tariff scheme, no hydropower project was retained but this may change if tariffs are reviewed to consider time-of-supply as well.
Hydropower is today not only subjected to climatic conditions, but there has even been a call from some Singaporean experts working on water sector reform to halt the production of electricity from hydro and direct more water resources to domestic use. Such a strategy reveals a fragmented approach to resource management instead of a holistic consideration of the intricate links relating to climate, water, land-use and energy. The specificity of Small Island Developing States (SIDS) along with the necessity of sustainability as an ethical imperative needs to be recognised. Reconciling the hydropower sector with the vision, strategies and actions linked to Maurice Ile Durable (Mauritius Sustainable Island), a national programme to promote sustainable development, is also a necessity. Least-cost dispatch at marginal cost of generation may have to give way to integration of environmental and social costs.
- Over the decades, there have been several deviations of natural watercourses both on the surface and underground. The carrying capacity of rivers has dwindled with the construction of roads and buildings. Wetlands have been destroyed. Flashfloods are now becoming more common. There is a need to assess holistically in economic, social and environmental terms the potential of hydropower in Mauritius. Opportunities like peaking through hydropower and storage for possible domestic use have also to be analysed. Sustainability criteria like those to be developed under the MID Compliance Mechanism have to be applied.
- A key parameter in power systems management is maintainability and maintenance planning. To face peak power demand whilst avoiding investment in additional capacity, particularly running on fossil fuels, it is vital to optimise the availability of hydropower facilities. Although their maintenance is relatively easy, the timing of repairs and other shutdowns has to be wisely set. A holistic approach is again needed, for example, taking into account seasonal factors like rainfall, biomass production and even the occurrence of heat waves triggering power demand. The possibility of having 100% availability of hydro facilities during the critical months of February and March should be a key target.
- Power systems planning currently considers a fixed availability of 25MW of hydro throughout the year. A more detailed methodology is required considering the complexity related to water availability for hydropower in space and in time. Storage possibilities have to be assessed also.
- The feed-in tariff scheme launched by the CEB has been fully subscribed tallying a total of 2MW. There is a need for other innovative schemes of decentralised power generation, integrating micro and mini hydropower together with storage (pumped or otherwise). This fits well in the policy of the government to democratise the energy sector engaging cooperatives, small planters and other stakeholders. The Maurice Ile Durable (MID) Fund as well as the Renewable Energy Development Fund are possible sources of financial support.
- The National Energy Commission has recommended not only to pursue further studies on the feasibility of pumped hydro systems but also to look into sea-water pumping and storage. In line with the Government strategy to promote an Ocean Economy, this potential is indeed of high holistic pertinence.
The way forward
The potential of hydropower in Mauritius is widely acknowledged to have been almost fully tapped. However, qualitatively, there is the opportunity to use the potential to face peak power demand, to enhance water storage and availability for domestic and other purposes, and to create synergies with national endeavours for renewable energy development, Maurice Ile Durable and Ocean Economy projects. Above all, in the context of efforts to decentralise energy production, the prospect exists for democratisation of the energy sector. The optimal use of hydropower can serve towards the ultimate goal of achieving sustainability, a most pertinent aspiration for a small-island developing state.
Assoc. Professor Khalil Elahee, M.A (Cantab.), PhD, Faculty of Engineering, The University of Mauritius, Reduit, Mauritius