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Classification of mini hydro power plants

The term ‘mini-hydro power plants’ refers to plants with a capacity below 10 MW according to the UNIDO (United Nations Industrial Development Organization) classification. Its modest size helps to reduce pressure and environmental impact. Mini hydro power plants are classified as follows:

  • pico-plants: P < 5 kW
  • micro-plants: P < 100 kW
  • mini-plants: P < 1.000 kW
  • small-plants: P < 10.000 kW

Generally speaking, this classification is valid worldwide.

Another way of classifying mini hydro power plants is based on their functioning in relation to the method of water intake and storage:

  • Flowing water facilities: these do not have the ability to be regulated. Capacity during the year depends on the hydrological regimen of the watercourse. The amount of energy produced is strongly influenced by the capacity of the watercourse. This also represents the main limitation of this type of facility, as the production of electricity depends on the capacity of the watercourse that can be exploited, which by definition is variable throughout the year, resulting in variable levels of production according to the season. As can be imagined, for example, there is a greater production of energy in the rainy seasons.
  • Regulated flow facilities (storage): these can regulate water flow using daily, weekly or monthly regulation tanks. Regulation is linked to the tank’s storage capacity. They exploit the potential energy contained in the water collected in natural or artificial basins. The amount of energy produced depends mainly on the drop.

Mini hydro power plants are usually water flow facilities built next to rivers, streams or irrigation canals with a constant speed in relation to the instream flow (an index of the maximum decrease in the flow of a watercourse downstream of the intake system) required to protect the ecosystem.