As part of the UK government’s climate change strategy, which will replace the existing Non Fossil Fuel Obligation, trade and industry secretary Stephen Byers is telling power companies to treble their use of renewable energy sources or face financial penalties. At present about 3% of energy in the UK comes from renewable sources but the government is aiming to increase this to 5% by 2003 and 10% by 2010.

Hydro power schemes greater than 10MW do not qualify for this new strategy but small and micro hydro can make a significant contribution to the UK renewable energy market. Ultimately officials believe the market will decide which renewable schemes are most cost-effective, and so hydro’s success could be determined by the cost of overcoming environmental barriers.

Great emphasis is placed by the UK Environment Agency (EA) on the need for environmental impact assessments (EIAs) at potential hydro power sites. These EIAs may identify additional work, such as constructing fish ladders and measuring and recording flows, before new projects are permitted. The cost of these measures, however, can make projects unviable.

The river Thames for example, has a great potential for hydro power production but development could be hindered by the fact that only three of the 45 locks/weirs on the river have water level measuring devices which provide a crude method of interpreting river flows. More accurate flow measurements can be obtained from ultrasonic gauging but at present this technique is performed at only seven sites over the entire length of the river, specifically where flood warnings are a great concern.

But why burden hydro power with flow measuring when there is no need for it? What is the purpose of measuring and recording flows which, if they do not pass through a turbine, will only flow unrecorded through control gates and over weirs? Turbines by their very nature are measuring devices and can be used effectively to control river flows and maintain water levels.

The EA also requires fish passes to be installed at run-of-river hydro power sites. On the Thames fish passes have been installed as far up as Mapledurham, to provide access to the valuable clean, cool water and gravel beds of the river Kennet. According to a member of EA staff, historically there are no records of salmon, sea trout or eels migrating further up the Thames than this region. Although salmon have been encouraged back into the Thames, progress is disappointing despite the installation of fish passes. Around 190 salmon tagged over a period of time have later been caught in the Irish sea and in other rivers. It is possible that pollution, and boat traffic in the Thames, is also contributing to this problem.

The Thames is like many other UK rivers with weirs which are necessary for flood control and navigation but rarely used for hydro power. Indeed, Mapledurham is the only Thames weir that uses a little water power at weekends for milling flour. Yet many weirs and mill sites, such as Buscot and Hambleden, still have water turbines onsite dating from the 1930s. Private dwellings, hotels and even villages could utilise these and become self-sufficient by using renewable hydroelectric power.

The EA estimates that it has 200 mill sites in the upper Thames region. Over its navigable length from Lechlade down to Teddington, the Thames falls 76m over a distance of 209km. Hydro power generation is possible at the 45 weirs on the Thames which have a fall in the range of 1-2.69m, with substantially useful flows providing power outputs up to 1500kW.

Sandford weir

In the 1970s, Sandford weir near Oxford still had a paper mill adjacent to the lock with a series of vertical shaft Francis turbines powering the mill. In the 1980s the mill was demolished and replaced with waterside apartments and the turbines were destroyed. The power for these apartments was brought in by the electrical grid system, adding to global warming.

However, Sandford weir has a head of 2.69m and usable flows of 30m3. Higher flows up to 350m3 do occur at the weir but are not worth considering due to decreasing head loss and a low percentage time available. After allowing for minimum flows and water for passing boats through locks, it is possible to have an installed capacity of 500kW at the weir. The water for this power is at present passed by level control gates which are operated manually by the lock keeper. No records of flow are kept but the number of lock operations and boats passing through each day are recorded.

The operation of the lock may consume 1000m3 each time it is used, depending on the number of boats and their displacement. In very dry periods, usually between June and September, river flows can be so low that the number of lock operations per day have been limited in order to maintain the water level above the weir for navigation.

In normal years there is an adequate surplus of water but in the wetter months, between October and April when there are fewer boats active on the river, there is a significant potential for hydro power generation. Throughout Europe and the world many run-of-river hydro power stations do not operate for three to five months of the year in the drier seasons, but their energy contribution is significant and important for the rest of the year.

At present large amounts of water (250m3 at Buscot and 4000m3 at Teddington) are released each time a lock is operated, passing filth and silt which discolours the water and disturbs oil polluted sludge. Engine driven boats also pollute and contaminate the water. In contrast, and by the EA’s own admission, water turbines pass a relatively steady flow of water which is controllable, improves water quality, screens out rubbish and acts as monitoring stations for pollution. Hydroelectric power at Thames weirs would enable flood control systems to be operated remotely from the new embedded generation.

At present, of the 45 Thames weirs:

•No power is generated but there is a potential installed capacity of 25MW.

•All of the water is passed unmeasured.

•Only 22 weirs below Mapledurham have fish passes.

•Water flows in the Thames via locks, weirs and control gates.

•Rubbish is not removed but flows on downstream.

The story of hydro potential on the Thames is repeated across the UK. An estimated 20,000 run-of-river weirs and mill sites in the country have the potential to generate 600-1000MW of renewable electrical energy.