Obviously, the harnessing of very low heads is only possible when there exists a hydraulic diversion infrastructure creating the potential head. However, even in this case, their profitability comes up against the following facts:

  • The use of low heads requires the use of significant flow which must be processed in adapted infrastructures, thus of respectable size;

  • Manufacturers have always privileged the size and cost decrease of their equipments to the detriment of civil engineering;

  • The cost of civil engineering rapidly becomes a deterrent as compared with the installed power and thus with the generated added value;

It is of primary importance to reach a profitable solution to optimize the costs of construction works. The following chart shows the exponential increase of the concrete volumes required for the construction of a hydroelectric power plant as the head decreases. It is based on statistical studies performed on many real cases and hydraulic calculations for the sizing of intake and draft tube.

For heads < 3m the impact of concrete volume (i.e. costs for civil works) soars incredibly!

 

 

As an example, it can be seen that for an equal power, when coming down from a 3 m to a 1.5 m head, the concrete volume necessary to install a conventional solution is multiplied by 5.

The original design of the VLH turbo-generator unit enables overcoming this difficulty since it reduces civil engineering works to their minimum.

The following sections are comparing the existing technologies for very low head sites regarding the size and complexity of the Civil Work structures.

Axial turbine with upstream elbow

Vertical Kaplan

Ecobulbe inclined position with a building

Ecobulbe inclined without building

VLH


It is clear that the VLH offers a shorter lay out, with very simple shapes and less excavations.

The civil engineering infrastructures necessary for the installation of a VLH are thus reduced to their most basic expression, limiting themselves to two parallel vertical side-walls and an horizontal bottom platform. The excavation volumes are also optimized thanks to the unit inclination.

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