Current technology allows to take advantage of the water power to generate electricity both in natural water courses (rivers…), as in artificially ones (channels, pipes…).
It is important to know that a mini hydraulic plant is not a big hydropower plant at reduced scale. An installation of some hundreds of kW has a completely different design from another of some hundreds of MW design and the equipment used in both cases is also different.
All mini hydraulic power plants have the following components:
1. Civil work installations
2. Electro mechanic equipment
Civil works includes the infrastructure and facilities needed to derive, drive and restore the turbinate water as well as to accommodate the electromechanical equipment and the general power system and its control. These infrastructures are:
Closing and adjustment elements. If the unit stops, the existence of devices that isolate the turbine or other working bodies is essential. Those are gates and valves.
The electromechanical equipment is composed by: turbine, generator and other electrical equipment necessary for the conversion of hydraulic energy into electricity and its disposal to the grid.
The key element in any hydroelectric power station is the turbine. Hydraulic turbines are classified into two groups: impulse turbines and reaction turbines.
Impulse turbines are those that take advantage only of the speed of water flow to turn them. The most used is the so-called Pelton wheel. Basically consists of a wheel (or impeller) equipped with spoon-shaped buckets on its periphery. This turbine is very efficient when the available water source has relatively high hydraulic head at low flow rates. Other types of impulse turbines less-used are: the turbine Turgo and the cross-flow turbine, also known as Ossberger or Banki-Michell turbine. The first one has been developed from a modification of the Pelton turbine, resembling its impeller to a Pelton but split in half. This turbine is used in middle slope waterfalls and low flow. The Ossberger turbine impeller has a cylindrical shape, with multiple blades arranged as generators. This turbine is very well suited to all kinds of waterfalls and flows.
Reaction turbines have a rotor design that allows taking advantage of the pressure that the water still having at its entry to convert it into kinetic energy. The most commonly used reaction turbines are the Francis and the Kaplan. The Francis turbine is very well suited to all kinds of waterfalls and flows. It is the hydraulic turbine most widely used in the world. The Kaplan turbine is generally used for small falls and large or variable flows. Its appearance is similar to the propeller of a boat.
Technological innovation has allowed appearing in the market substitute components of classic turbines, with different geometries. New patents for hydraulic plants with very low falls have been developed in order to make economically viable its energy use. Such is the case of Archimede’s screw or screw pump. This screw is a helical gravimetric machine used traditionally for water elevations, flour, cereals or excavated materials. This application is used in small waterfalls with low water flows that actually cannot be exploited with the turbine technology.