Run of the river hydro

Posted by Rod Ellison on 24/03/2011

Since the introduction of the feed in tariffs in April 2010 the UK has seen a massive resurgence of interest in small hydro projects. The projects in the main have been run of the river schemes which make use of water in a watercourse as it passes through rather a location rather than storing it behind a dam. Run of river projects are dramatically different in design and appearance from conventional hydroelectric projects which store enormous quantities of water in reservoirs, necessitating the flooding of large tracts of land.

In contrast, most run-of-river projects do not require a large impoundment of water. The majority of schemes in the UK are in the power range 25 kw to 1 MWe and in addition to power output it is important to consider annual energy output from the scheme which is a function of the engineering design and hydrological factors. So, what exactly are the benefits to be expected when using these systems? Hydro power offers a host of advantages, not only to the users, but also to the electricity suppliers and the environment: 

Renewable - as with wind and solar power, hydroelectric is a renewable energy. It does not rely upon other resources, such as coal, uranium or gas, to generate power. Furthermore it does not suffer from the extremes of intermittence that typically affect some technologies.

Limited emissions – so long as the construction phase is suitably managed the risk that sediment and oils will affect local water resources is limited. During operation limited waste products are generated (parts from servicing and material cleared from screens) especially when compared to fossil fuel and nuclear plant.

Adaptability - hydroelectric power stations can be built to any size, depending on the river or stream used to provide the water source. This means that the stations are highly adaptable, and can vary in size, from small stations to power one household, through to larger builds to power entire towns.

Long operational life – generally speaking moving parts are under quite low stresses operating under very steady loading conditions with no sudden load changes; as such the systems have potentially long operational lives with limited maintenance.

Consenting - the projects require planning permission and various permissions from the Environment Agency (England) including Flood defence consents and Abstraction and Impoundment licenses. Obtaining these licenses and permits is far from a simple process.

Environmental Impact - small, well-sited run-of-river projects can be developed with minimal environmental impacts; but as for most developments the devil is in the detail. The key is accurately understanding baseline environmental conditions and how these conditions will be modified by the realisation of the scheme.

During the design phase modeling of how modifications to the fluvial regime interplay with aspects such as sediment transportation, the nature of river beds and of course species reliant upon is part of the iterative design process. This study should include aquatic species (chiefly fish and invertebrate species) and species using the river corridor but land based. As for any infrastructure a balance has to be struck between the pressing need to de-carbonise and de-centralise our energy infrastructure and the quality, diversity and long term integrity of our natural environment.