Micro hydroelectric plants

The expression “Micro hydroelectric” is referred to an installation that don't exceed 100 kWh of production, within this category we find an additional category related to plants that are destined for self-consumption and produce less than 5 kWh called "Pico-hydroelectric".


The most used turbines in this kind of applications are the Pelton or the Banki (also called Cross-Flow).

The minimum requirements for a correct installation are the following:

  1. A geodetic head on the site of the installation (even a few meters)
  2. A minimum water flow rate (even only 0.5 liters / second), not overly conditioned by the season and fairly constant over time.
  3. Possession of the concession for the derivation of surface public water for hydroelectric use (in Italy for example the entity responsible for this authorization is the Province)

As for photovoltaics, even in the case of hydropower, the plant can be Off Grid (independent) or connected to the grid and therefore be able to sell energy to the national grid.

  • Off-Grid Installation: The Off Grid Installation is often used even if the production is very low (few kW), and for utilities without a connection to the grid (such as mountain shelters, farms or small isolated communities),small powers are however useful in fact because generally the water is always present 24hr a day so even a production of a few hundred watts, combined with a storage system, is able to provide the energy for feeding an house or a shelter.
    For example, a pico-hydroelectric turbine that produces "only" 400Whr, once combined with an accumulation system, is able to accumulate and supply in a day 9.6 kWh which is more than the consumption of an average family!
    The amount of excess energy that is not used is dissipated in appropriate resistances, in some systems the heat produced by these resistors can even be used to heat sanitary water, bringing the user to a greater energy independence.
    A further advantage of these systems is linked to the fact that they are highly automated and therefore require only routine maintenance.
  • Grid installation: In Italy for example if a system is connected to the network, the options are substantially two, if the installation has been in operation after January 1, 2013, in fact you can use the all-inclusive tariff or alternatively the on-site exchange service (up to a power of 500 kW).
    • All-inclusive Rate: You are entitled to the all-inclusive tariff only if you have small plants, specifically if the plant is less than 1MW of production and falls within the regulations of Ministerial Decree July 6, 2012 or if the power is less than 500 kW and falls within the discipline of the Dm 23 June 2016.
      The all-inclusive tariff is an incentive that is recognized for a period of 20 years and is measured on the basis of the kW produced according to the following criteria:
      • € 0.257 / kW with plants < 20 kW
      • € 0.219 / kW with systems between 20 and 500 kW
      • € 0.150 / kW with systems between 500 and 1000 kW
    • On-site exchange: The on-site exchange (SSP), governed by the resolution of the Authority for Electricity and Gas, defines the regulation of the mechanism that allows the introduction into the grid of the electricity produced by a private production plant. The on-site exchange service in Italy is regulated on an economic basis by the Energy Services Operator (GSE) in the form of a financial contribution associated with the valorisation, at market prices, of the energy exchanged with the electricity grid.

How much does it cost to build an hydroelectric installation?
It's always difficult to establish the cost of an hydroelectric installation because construction works (such as intake channels or damming structures) often have a heavy impact on the investment.
As regards the mechanical part, that is, the realization of the turbine, the principle of economies of scale is valid, so the more the turbine grows with power the more the proportional cost decreases, basically this mean that if the turbine is small in proportion what it produces will certainly cost more than the same turbine with a higher production capacity in terms of kW.
To this rule, however, there is an exception for pico-hydroelectric installations, since for these a civil work is often not necessary.
Another advantageous aspect of the micro / pico plants is linked to the fact that they do not need, due to the high automation, supervision by dedicated personnel.
It is generally possible to estimate a cost for small plants around € 3000 for each kW installed, For powers under 3kW with the building work the installation can reach up to about 10.000 € / kW.
We can calculate that the investment will be amortized in about 15-20 years for installations between 10 and 100 kW and in less of 10 years for smaller plants.
These economic results are advantageous also if we consider that htdroelectric installation have a really long life (about 50 years) and a high utilization factor (from 3000 to 5000 hours per year).

What are the main components of the system?

  1. For users connected to the network:
    1. Hydraulic turbine: The heart of the system and, in general, constituted by a fixed organ "the distributor" and a mobile part known as "the impeller". The distributor canalize the incoming flow to the impeller and adjusts the flow; the impeller transforms the received energy.
    2. Generator: It produces electricity received from the turbine and is capable of working at different speeds, offering a high efficiency in the transformation of mechanical energy into electricity, generally between 80-85%.
    3. Holding Point Quote
    4. Electrical panel: The control device that regulates the energy flows to the points of use, transforming the voltage and keeping it stable.
  2. For isolated users we will have the same components and also:
    1. Dissipator: It's a component that can dissipate the energy produced by the plant and not immediately used by the user in order to prevent the system from going into short circuit.

What permissions do I need?

With the concession the PA constitutes in favor of the concessionaire a "temporary right" to subtract water from the general use in order to allocate it to a particular use (only if this is compatible with the public interest) according to a specific use project.
The authorization procedures for the construction and operation of the installation are activated only if the concession to derive is obtained.
The concession in Italy is usually carried out by the province for plants with power below 3000kW and by the region for larger power plants, the elements taken into account are the following:

  • Holding point quote
  • Point of return quote
  • Average annual flow
  • Maximum capacity allowed

We can summarize the following steps:

  • Grant application accompanied by preliminary draft;
  • Start of proceedings (if appropriate project);
  • Publication BURL notice of the instance: any competing instances;
  • Possible Verification / WAY or Impact Assessment (SIC / SPA)
  • Technical-administrative investigation (unified with concurrent requests) and required mandatory opinions (eg opinion of the Basin Authority, Hydraulic Authority, Competent Authority on safety withholdings, etc.); Release / rejection of concession with the choice between competitors (with the same project the first instance) and acceptance / disciplinary signature of the concession.


Duration of proceedings:

For hydroelectric use there is an increase in the "administrative" time of the procedure due to the sum of 2 iterations:

  • Obtaining the concession to derive (18 or 24 months if VIA);
  • The authorization "s.l." to build and operate the plant (CEL, PAS or AU).