Environnement et petites usines hydroélectriques

Abstract

The rise in the price of oil products has, in France as elsewhere, enhanced the value of other energy sources. Recent decisions are in particular intended to facilitate the development of small hydroelectric plants, which in certain areas are the only cost-effective ones. However, it happens that the changes made to the aquatic environment are sometimes out of ail proportion to the amount of energy that can be expected from them, as these installations are often sited in the last remaining natural zones in mountainous regions or on those rare sections of watercourses that have not yet been developed. The effects of small hydroelectric power stations on the environment are not significantly different from those of larger installations. Building an obstacle to the natural flow of the river and the diversion of ail its water result in substantial modifications to the hydrological regime of the watercourse, the speed of the current, the extent of flooded zones, the transport of sediment, water temperature, and the possibilities for diluting polluting effluents. These modifications tend to impoverish the aquatic flora and fauna, leading to the disappearance of the most sensitive species, which are often the rarest. The result is often a very homogeneous environment; this tendency affects ail the species, and in particular the fish population, with the disappearance of the Salmonidae. The scenery, too, is often altered by the architecture of the installations, the movement of earth, the creation or widening of watercourses, and deforestation, particularly in mountainous areas, thus removing the interest from a natural countryside which is often of exceptional beauty. Since hydroelectric energy has already been exploited for a long time in France, most of the sites with a useful energy yield have already been equipped. Thus, in the Ariege departement in the Pyrenees, nearly three quarters of the large rivers have been diverted from their natural beds, and the flows maintained in the river are quite inadequate to ensure preservation and diversification of the aquatic flora and fauna. The situation is the same for numerous rivers in the Alps and the Massif Central. New hydroelectric power stations can therefore only be built in those last sections of the watercourses that have not yet been developed and which consequently often have a considerable value as part of the national heritage. For this reason, regulations have recently been published to control the construction and operation of such installations in order to ensure that the project does not deteriorate the local environment too much: the authority responsible for the future station is required to present a complete impact study measuring the effects of the various proposed installations and of their operation on the aquatic environment and on the countryside. This implies that first of ail a careful inventory must be made of this environment and this countryside. Based on the results of this impact study, various constraints are then imposed on the operator; these concern in particular the flow to be maintained in the natural bed of the river, and in general this flow must not be less than the normal flow in the driest month of the year. Similarly, the power lines have to be buried and the architecture of the buildings made to conform to the traditional local style. These measures also lead to the establishment of a programme for the use of the waters in each hydrographic basin, by ensuring balanced energy development that enables the other uses made of the water to be preserved, including those for leisure purposes, and the quality of the environment to be maintained. Series C. (3 to 25 m of head, 2 to 50 kW) This series exists in several versions for operation out of the water or immersed. These small sets, which are of simple design (no multiplying gear) and robust construction are ideal for quantity export (developing countries). These micro power stations are delivered with complete electrical equipment for use either on an isolated autonomous network or interconnected with other energy sources. For isolated networks, Leroy Somer has developed an electronic energy-absorption regulator which stabilizes the electrical characteristics (voltage 0 ± 10%, frequency 0 ± 0,5 %). On an isolated network this electronic regulation enables asynchronous generators to be used, with ail their advantages: robustness, reliability, price. The ease of use and performance are comparable to those of a normal generating set, without its disadvantages (less reliability, maintenance). The development of micro power stations assumes that competent engineers are available for the consultant studies (hydrology, civil engineering, electricity distribution), which represent an important part of any project. Despite certain difficulties which are being experienced, there would appear to be an assured long-term future for micro power stations both in the industrialized countries and in the Third World.