The original features of the VLH provide it with extremely favorable environmental characteristics.
Being the VLH unit submerged, its visual and noise impact is very low, thus making its implementation in urban environments very easy as in the case of the demonstration site located in the heart of the city of Millau, in the immediate proximity of dwellings and of the local camping ground.
However, the most interesting feature regarding the environmental impact of the VLH lies in its very low impact on fish migrations.
Such very specific characteristic led us to adopt a neologism able to sum up the concept in a single word: “fish-friendly”. Such neologism has been deposited and henceforth used in order to summarize the VLH ability to let fish migrate through its operating blades.
The VLH turbo-generator unit is the first hydroelectric turbine for which the fish friendly characteristics have been taken into account as basic data, from the origin of the equipment design.
In fact, its very large wheel diameter provides large spaces between guide vanes and between blades, enabling easy passing of all river fishes. Furthermore, the wheel rotation speed is very low (<40 rev/min) and the water flow speed inside the wheel remains below 2 m/s (comparable to that of a fish passing). Finally, the hydraulic passage is characterized by very low pressure variations.
All these objective data have already allowed, for the authorization of our Millau demonstration site, to avoid the installation of protection devices (fine screens, drain flows, etc.) preventing the downstream migration (passing of fishes from upper to lower waters) through the turbine wheel.
Studies and tests under scientific supervision have been performed in collaboration with the "Office National de l’Eau et des Milieux Aquatiques” (ONEMA) on the Millau demonstration site, on the Frouard HPP on the Moselle river and then on the La Glacière site in Millau in order to confirm the downstream migration capacity of the VLH turbo-generator unit.
Their excellent results rank the VLH as first among the most fish-friendly turbines tested up to the present day. Tests have also enabled to make modifications on the VLH to further improve its performance within this field.