Harnessing water's potential: What is hydropower?

Rising energy prices and the fight against climate change are giving a fresh boost to hydropower, a well-established renewable energy source.

The Ancient Greeks used the mechanical power of falling water to turn wheels, which then ground wheat into flour, and it had an important role to play in industrial revolutions in Europe and the US by powering small factories before coal became widely available.

Hydropower can be divided into small and large hydro. Definitions vary from country to country, but small-scale projects tend to be below 10 MW in size.

Despite significant technological advances, the principles underlying hydroelectric power have not changed since the first plants were constructed in England in the late 19th century.

How does hydropower work?

The most common method of generating hydroelectric power is by damming rivers to store water in reservoirs. Upon its release, the flow turns turbines, which then generate electricity.

Hydropower does not necessarily require a dam, however. Small hydropower often simply uses canals or streams to produce enough electricity to light and run the appliances of individual households, for example.

The advantage of micro-hydro is that it can be used to power houses close to rivers, especially in areas where grid connection is expensive. It is also more discrete than conventional hypropower, and does not interfere with local ecosystems.

Hydro is by far the largest source of renewable electricity, covering around a fifth of global demand. In Europe, Norway leads the way, producing 98% of its electricity from hydro. Other European front-runners include Switzerland, Sweden and Austria, which all come close to 50%, according to World Bank statistics.

Renewables policies working

The arguments in favour of hydro power are many. Generation costs are generally lower than fossil fuels, which attracts business. Moreover, water is an indigenous resource and provides greater energy security.

Nevertheless, the environmental hazards of large dams are well-documented. Studies show that modifying river flows and contours reduces fish stocks and causes silt build-up and temperature fluctuations.

Conversely, changed political priorities towards climate protection have led to significant capacity growth in recent years.

Developing countries have the greatest potential for new capacity. Although the most suitable European locations are already in use, experts say that there is significant scope for technological improvements. In Western Europe, new capacity may be generated by upgrading existing installations to gain efficiency, while Eastern Europe could refurbish ageing plants.

Moreover, a European Union directive on promoting renewable energies aims to source 20% of the bloc's energy mix from renewables by 2020, significantly boosting hydropower. The European Small Hydro Association (ESHA) estimates that around a third of potential small hydro capacity could be developed by 2020.

Hydropower plants with pumped storage will particularly benefit from promoting renewables as they facilitate use of intermittent renewables like wind or solar. Systems capable of pumping water up dams to store electricity for release at peak demand hours can balance power production as more intermittent sources are integrated into the grid.

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