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Everything you need to know about Hydropower.

- categories: blog

Everything you need to know about Hydropower.

What is hydropower? 

Hydropower is a renewable energy source that converts the energy in moving water into electricity. It has been around for many years, historically found in the form of water wheels in mills. Modern hydro plants can range from micro-scale (typically <100kW) to large-scale which can reach up to hundreds of MWs in size. In 2015, hydropower accounted for 16.6% of the world's electricity generation and it is currently produced in 150 countries. 

Small-scale projects are typically located in rivers and streams with a high head (the amount of mechanical energy available in the water) and flow rate. Larger projects involve a dam that stores water on the upstream side of the dam, known as an artificial lake. At this stage water is stored in the form of potential energy. Once the water is released downstream from the artificial lake, through the penstock, the stored potential energy is then converted to kinetic energy. The flowing water spins the blades of a turbine that is connected to a generator and produces electricity. 


Why use hydropower?

  • The main advantage of hydropower is that it utilises a renewable resource (water)
  • For dam hydropower plants the reservoirs can be used as a means of flood control
  • For small-scale projects, running costs are low (low maintenance requirements)
  • Some hydro plants can be used as a response to unexpected spikes in electricity demand as they can go from zero to maximum output extremely quickly

Is there a downside?

  • One of the biggest disadvantages of hydropower is the environmental impact of the construction, for example concerns for the ecosystem, water quality and potential for pollution affecting aquatic life
  • For large-scale dam projects, significant quantities of cement are used in the construction process, therefore there are greenhouse gas emissions associated with the manufacture of the cement used in the plant
  • For small-scale installations in rivers and streams, during the summer months there is likely to be a reduced flow rate, hence reduced power output

Is Hoover dam the biggest in the world?

Until 1948 it was the tallest dam and the largest hydroelectric plant in the world. Since then, larger plants have been constructed, however Hoover Dam is one of the most famous and most visited with 7 million visitors per annum. The Hoover Dam hydroelectric plant, located on the Arizona-Nevada border is operated by the Bureau of Reclamation. It is made up of 17 turbines (totalling 2,080MW) that generate about 4 billion kWh annually, enough to serve 1.3 million people in Arizona, Nevada and California.

Closer to Home

The Turlough Hill pumped storage hydropower plant (capacity of 292MW), located in the Wicklow Mountains and has been operational since 1974. It is Ireland’s only pumped hydropower station and is owned and operated by ESB. Pumped storage hydropower stations, however, differ to conventional hydropower stations.

How does pumped storage hydropower work?

  • Two reservoirs are utilised as opposed to one, the upper reservoir and lower reservoir
  • Water from the upper reservoir is released and moves from the upper reservoir to lower reservoir through a 584m pressure shaft pipe and through the four 73MW pump turbines to generate electricity
  • During periods of low demand, the water is then pumped from the lower reservoir back up to the upper reservoir using a reversible turbine
  • The station can ramp up to full operational capacity in 70 seconds hence is a good resource for times of peak demand

The history and operation of Turlough Hill is explained in this short clip:


Hydropower is a well-established technology in many parts of the world on all scales. However, in Ireland and Northern Ireland there is still considerable unexploited hydropower potential at small-scale. As decentralised energy systems emerge in the future and the design of small and micro hydropower turbines and generators continues to develop, it is hoped that this will increase.

Micro-hydropower (MHP)

Micro hydro power is hydroelectric power that typically produces from 5kW to 100 kW of electricity. MHP can also be applied to water networks which often have excess pressure and constant reliable flows. Action Renewables are currently leading an EU project called ‘REDAWN’ – Reducing Energy Dependency in Atlantic Area Networks - which aims to improve the energy efficiency of water networks through the installation of innovative micro-hydropower (MHP) technology. This technology will recover wasted energy in existing pipe networks across irrigation, public water supply, process industry, and waste-water network settings. The REDAWN project brings together 15 partners from 5 countries around the Atlantic coast of Europe, working towards greater efficiency in water networks. The objectives of the project include:

  • Completion of an energy recovery resource assessment in water networks in the Atlantic Area (AA) region
  • Completion of an economic and environmental impact assessment for the region including assessment of the potential reduction in CO2 emissions from the exploitation of the identified resources
  • Construction of scale demonstration MHP pilots representative of 3 water industry sites selected from across the AA including irrigation, process industry and waste/storm water sectors
  • Development of business models/cases appropriate to successful exploitation across all elements of the supply chain
  • Development of design guideline and support tools for hydropower energy recovery in drinking water, waste water, irrigation and process industry sectors
  • Development of policy and organisation support tools and guidance to increase the implementation of energy recovery projects in the region
  • Quantification of the societal impacts of hydropower energy recovery in water network
  • Widespread dissemination and promotion of energy efficiency in AA water networks
Find out more about REDAWN and other EU projects


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