Hydroelectric power is generated by the flow and strength of running, moving or falling water from rivers, the sea’s tides or using larger man-made systems such as dams and reservoirs. Turbines placed within the flow of water extract its kinetic energy and convert it to mechanical energy. This causes the turbines to rotate at high speed, driving a generator that converts the mechanical energy into electrical energy. The amount of hydroelectric power generated depends on the water flow and the vertical distance (known as ‘head’) the water falls through.

There are 3 main types of hydroelectric schemes in use in the UK:

  • Storage Schemes:
    • A dam impounds water in a reservoir that feeds the turbine and generator that are usually located within the dam itself.
  • Run-of-river Schemes:
    • Run-of-river schemes use the natural flow of a river, where a weir can enhance the continuity of the flow. Both storage and run-of-river schemes can be diversion schemes, where water is channelled from a river, lake or dammed reservoir to a remote powerhouse containing the turbine and generator.
  • Pumped storage:
    • Pumped storage incorporates two reservoirs. At times of low demand, generally at night, electricity is used to pump water from the lower to the upper basin. This water is then released to create power at a time when demand, and therefore price, is high. Although not considered a renewable energy (because of its reliance on electricity), pumped storage is very good for improving overall energy efficiency
UK Hydroelectric plant distribution – Size of circle represents capacity.

There are 3 main categories used to define the output from hydroelectric power:

  • large-scale capacity: hydro plant producing more than 5 megawatts (MW)
  • small-scale capacity: hydro plant producing less than 5 megawatts
  • micro-scale capacity: hydro plant producing less than 50 kilowatts

Historic Trends and Growth

Interest in hydropower in the UK rose in the early 2010s due to UK and EU targets for reductions in carbon emissions and the promotion of renewable energy power generation through commercial incentives such as the Renewable Obligation Certificate scheme (ROCs) and feed-in tariffs (FITs).

Hydropower Capacity in the UK since 2010

Before such schemes, studies to assess the available hydro resources in the UK had discounted many sites for reasons of poor economic or technological viability, but studies in 2008 and 2010 by the British Hydro Association (BHA) identified a larger number of viable sites, due to improvements in the available technology and the economics of ROCs and FITs. However, during the same period there have been significant reductions in costs of other renewable energy sources such as Offshore Wind and Photovoltaics, this has resulted in reduced competitiveness of large-scale Hydroelectric schemes in the UK.

Schemes up to 50 kW were eligible for FITs, and schemes over 5 MW were eligible for ROCs. Schemes between 50 kW and 5 MW could choose between either. The UK Government’s National Renewable Energy Action Plan of July 2010 envisaged between 40 and 50 MW of new hydropower schemes being installed annually up to 2020.

There are no large-scale Hydroelectric schemes planned in the UK as of 2020. However, it is predicted that pumped storage will play an increasingly important role in the UK electricity grid in future years as more intermittent sources of electricity generation come online.

Percentage of UK power generated by Hydropower

Above shows a very slow 1% increase in percentage share of hydro in UK generation with very intermitted periods. The intermittent periods were compared to the UK rainfall over the same period:

Overlay of hydropower generation vs. UK rainfall

The figure above illustrates that during the initial growth of hydropower (2010-2015), the periods of high generation followed period of high rainfall. After 2015, this trend is not as obvious as UK rainfall has not reached the same magnitudes as in previous years; this is potentially a reason for the slowed growth of the generating percentage share as it is unable to keep up with the growing energy demand.

Future Analysis

It is unlikely we will see again the scale of development witnessed in the UK in the 1950s and 1960s. Opportunities to use this technology on a large scale are now limited, not only because of environmental concerns but also because many of the most economically attractive sites for schemes have already been used. However, it is important we exploit our remaining small-scale hydro resources in a sustainable way.

Some old watermills are also being refurbished and brought back into the energy supply network.

Studies from 2011 estimated there is a remaining viable hydro potential of 850 to 1550 megawatts in the UK. This represents approximately 1 – 2% of current UK generating capacity and so would make a modest but useful contribution to UK renewable energy and emission reduction targets. In short, there are no real plans for hydroelectricity in the UK, though just because new schemes aren’t set in stone doesn’t mean there won’t be more of a future!

Financing & Landowner Considerations

There are a number of steps that have to be considered before a scheme can be built, e.g. scheme economics, environmental permits, planning consent and connection to the local electricity network. However, by the nature of the remote and rugged geographic locations of some of these potential sites, in national parks or other areas of outstanding natural beauty, it is likely that environmental concerns would mean that many of them would be deemed unsuitable, or could not be developed to their full theoretical potential.

A number of people have already installed micro-hydro schemes. In general, even small-scale schemes provide enough power for a number of houses or a small community. Although upfront costs for hydropower are high, installations should last for decades. Low head installations can generate renewable energy 24 hours a day.

Hydro developers should contact the relevant local authority for specialist advice at the earliest stage before undertaking a feasibility study.

If you want to build a new hydropower scheme, you need to apply to the Environment Agency for:

  • an abstraction licence – if you divert or take water from a river or watercourse
  • an impoundment licence – if you plan to build a dam or weir to hold back the flow of an inland water, or if you plan to change an existing weir or structure as part of your scheme
  • fish pass approval – if you plan to install or modify fish passes as part of your scheme
  • an environmental permit for a flood risk activity – when you build in, over or next to main rivers (for rivers and watercourses that are not main rivers you must apply to your lead local flood authority for consent)

Contact your Environment Agency permitting officer if you’re unsure who your lead local flood authority is.

You must not cause harm to the environment while constructing or operating your hydropower scheme. Fish and other aquatic ecology can be very sensitive to changes in river flows.

Before you apply, you can speak to the Environment Agency to get more detailed information about the process of applying to build a hydropower scheme.

You should employ a specialist to help you design your scheme and make your application. You can contact the British Hydropower Association or the Micro Hydro Association to get help finding a hydropower specialist.

Full guidance for the application requirements to build a new hydropower scheme see the government guidance here.

Occasionally there are grants available. There is no UK-wide general hydropower grant scheme. Schemes that are available change frequently.

The current method of income for hydropower schemes is via the Smart Export Guarantee (SEG) which supersedes the FiT and RO schemes. However, this is limited to plants less than 5MW, which is not likely to be an issue for most hydropower systems.