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Hydropower

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Hydro systems generate electricity from running water. Whether it is a technology worth considering in your community is highly site specific. All hydro systems require a good year round flow of water (above 100 litres per second) and preferably a good height difference, known as ‘the head’, between the top of the scheme and the turbine (above 1.5 metres). In general, a head is created where there is a barrier in the river such as a weir, sluices or former water mill – although they can occur naturally where there is a slope or a natural waterfall.

The Technology

Hydro systems come in a wide range of designs depending on the water course and the generation capacity. Most systems require a head of at least 1.5meters. However, there are some “run-of-river” turbines that can be used in rivers with low head, provided there is sufficient flow. In general, rivers with low head but high year round flow are large watercourses.

Hydro schemes may require some civil works (e.g. digging deeper channels), and the capital cost of the civil works required can be prohibitive. Civil works may be needed on parts of the watercourse that do not belong to the micro-hydro scheme owner; access and work on these needs to be agreed with the owner. Former water mills offer some of the best sites for micro-hydro systems as the existing infrastructure can be adapted.

As well as planning permission from the council, licences and approval from the EPA are required. The EPA is particularly concerned about the impact of schemes on ecology, mainly on any migratory fish. Mitigating measures such as a mesh screen and a fish ladder may need to be installed. A fish ladder is a structure on or around artificial barriers to facilitate fishes' natural migration. Most fish ladders enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps into the waters on the other side.

The turbine and generator can be noisy, but good design can reduce the impact.

Operation and Maintenance

Small turbines should be inspected once a year, annual service costs should be no more than 1-2 per cent of the capital cost of the scheme. Most run of river schemes will have a 'trash rack' that prevents debris from reaching the turbine – this rack will need to be inspected and cleaned on a regular basis unless some form of automated cleaning system is included. After 10 to 15 years the generator may need replacing but the turbine is likely to have a life of well over 25 years.

Scale

Hydro schemes range in scale from micro-hydro schemes which can be less than 1kW up to very large multi-MW schemes found in mountainous regions. A 6kW hydropower system could generate approximately 26280 kWh of electricity – enough for around 5 and a half average homes.

A 75kW hydropower system could generate approximately 328500kWh of electricity – enough for around 75 average homes in the south west.

Commercial Considerations

Hydropower is a well established technology, with some electricity generating schemes in the south west dating back to before 1900. Hydropower turbines have a long lifetime of up to around 50 years. Capital costs for hydropower schemes are relatively high, especially if civil works are needed or mitigating measures such as a fish ladder are required.

Non-standardised costs are those additional costs incurred as a result of measures taken to reduce the environmental impact of an installation. Hydropower schemes are more likely than other technologies to incur non-standardised costs for example to install fish ladders or other forms of fish protection. The availability of grants for a hydropower scheme should therefore be investigated. A hydropower expert will be able to assist with identifying suitable grants.

Further Resources

PlanLocal video on ‘Hydro power: an introduction’.