The Technology Context – B101

The Severn Barrage, is it the best way forward for tidal generation or is there another way?

An introduction to renewable energy and tidal power

Renewable energy is a massive, very important and relevant modern day issue. Everyone is looking at reducing carbon emissions and so sustainable technologies come in to play. There are many different types of renewable energies which include Solar, Wind, Geothermal, Hydroelectric and Tidal Generation. Solar and hydroelectric generation are not ideal for England and Wales. There is not enough light intensity throughout the year for solar and there are few places where hydroelectric plants can be built. Geothermal is virtually unused in the UK as it would not be cost effective due to the geology. The most viable renewable resources in the UK appear to be the wind and tides. Wind power is quite expensive whereas the predicted costs, for example, of the Severn Barrage Tidal Power Generator come well in line with those of current coal fired power stations. In the case of tidal lagoons they are projected to undercut the costs of nuclear generation.

Harnessing the Blue Giant

In recent years it has become more and more apparent that we need to find green, renewable and sustainable technologies to replace the current ageing and polluting coal, oil and gas fired power plants. These fossil fuel resources are steadily being eaten away and will not be there forever. It is a very real fact that we are eventually going to have to look for alternatives so why not invest and do it now rather than wait till we have run out of fossil resources?
The sea and its tides are one resource that the UK has in abundance. For many years people have recognized and studied ways of harnessing the huge power of the sea and its tides as massive amounts of water move around the earth creating the tides every day. The most common approach to this is using a turbine that is turned as the tide flows through or over it and powers a generator.

The Bristol Channel as a Power Plant

The Bristol Channel has the largest tidal range in the UK at 8 metres and would be a great place for a tidal generation plant. The proposed Severn Barrage from Brean Down to Lavernock Point has been in the pipeline for a long time. There are also several other proposals for the Bristol Channel one of which is for tidal lagoons in the shallow water around the estuary. These lagoons are at present the biggest competitor to the Severn Barrage. Tidal Lagoons are projected by some people to be a better, less damaging and more efficient sustainable development project. These are both large scale and expensive sustainable projects and will need a large financial commitment from the UK. Both will drastically alter the ecology, tidal streams and current in the Bristol Channel. Due to these political, financial and ecological issues great consideration needs to be given to which, if either, is to be built in the estuary, taking account of the long term effects.
There are many ways of generating power from tidal streams. Most are based around a propeller blade or enclosed turbine aligned under water to the tidal streams. These are vulnerable to being damaged by passing vessels, particularly pleasure vessels, that are unaware of their existence They are also relatively inefficient, hard to maintain and expensive due to the cost of underwater piling and cable laying. A fairly new and innovative idea is impounding water and then releasing it through turbines. There are two basic types, The Tidal Barrage, an impound wall across a river estuary and The Tidal Lagoon, a circular impound wall offshore in relatively shallow water, both of which have turbines built into them.

So how does it all work and what will it do?

The tidal barrage which has been put into actuation in the La Rance Estuary in France is a river barrage. The basic principal is that river estuary is blocked by a wall which has sluices and turbines built into it. The tide is allowed to flow in behind the barrage until high tide then at high tide the sluices are closed. The water is held and then released through turbines that power the generators. The Severn Barrage from Brean Down, in Somerset, to Lavernock Point, in South Wales, will be an approximately ten mile concrete and aggregates barrage impounding one hundred and eighty five square miles of the estuary (Friends of The Earth, Jan 04) . According to a sustainable development commission report (SD Commission July 07) the proposal is for it to have up to two hundred and sixteen low speed generating turbines with a nine metre diameter and one hundred and fifty, twelve metre square sluices. The low speeds and open sluices allow for easy passage of fish and marine life. It will have an installed capacity of 8640MW which is massive compared to the 240MW of La Rance, currently the largest tidal generator in the world. The barrage could produce about 5.4% of England & Wales’ current electricity demands each year.



At present there are no examples of tidal lagoons but they work on a similar principal to barrages. The difference being it can essentially be developed anywhere within a high tidal range at relatively low cost (R-Energy report retrieved January 08). Allowing tide in through sluices, trapping it and releasing it through turbines. According to a study by Friends of the Earth, the biggest example proposed for the Bristol Channel would impound a massive area of one hundred and fifteen square miles with a ninety five mile long wall around it. This would give it an impressive installed capacity of 4500 MW which while less than that of the tidal barrage is only the maximum peak performance. On average it has a higher output of 2.75 GW compared to 1.95-2.17 of the barrage as it can operate for a longer period over each tide. This huge lagoon is projected to be able to produce close to 6% of England and Wales’ current electrical demand.



Both the barrage and lagoon scheme will require large amounts of material to build, the barrage requiring thirteen million tonnes of aggregates compared to the lagoons estimated two hundred million tonnes (Friends of The Earth, Jan 04)Even though there is a vast amount more aggregates used for the lagoon there is a limited amount of concrete needed. Any rubble, hardcore or slag for example from mines or demolition can be used. This reduces costs as the cheapest available material can be used. Both are designed to last at least one hundred and twenty years although they can quite easily last significantly longer. Their composition means they are unlikely to be affected by earthquakes and could be easily repaired by adding more aggregates if damaged. The barrage is slightly more vulnerable with large concrete sections but it is unlikely that it would suffer severely from this kind of event.

The Politics

An R-energy Report (R-Energy report retrieved January 08) comments that “The company Tidal Electric promotes tidal lagoons and argues that because lagoons can be built without being constrained by geomorphologic features, greater consideration can be given to the environment. Migrating fish can swim around unimpeded and without the danger of negotiating sluices or turbines.” Scientifically delicate microsystems can be avoided altogether and left untouched. Lagoons will not affect the tides coming and going in the way that a barrage would. Far from destroying habitats a lagoon would increase the number of habitats available by actually adding a calm water lake. R- Energy (R-Energy report retrieved January 08) reports that large ocean predators would not be able to hunt in the lake. Therefore, smaller fish are likely to flourish, potentially providing significant feeding grounds for birds. In addition the ninety five mile aggregate wall would create a vast artificial reef. This would further enhance the local habitat potential, increasing the opportunity for improved marine life.
AEA Technology, engineering advisors to the government, are confident of their methodology and that the technology will work, environmentally and financially (Thorpe, T.W., (2002))AEA say the lagoon system, while using tried and tested technology is still a new concept. Prior to constructing a large scheme in the Severn, Tidal Electric is planning to test the concept in Swansea Bay with a relatively small 30MW output plant. So as to give them a better understanding of the effects that such a project might have on the environment and highlight any shortfalls.
The Welsh Secretary Peter Hain said, with regard to the barrage scheme, “It compares on a scale with the Channel Tunnel. Apart from this it is above ground for everyone to see.” (ICWales, Oct 07). He is also quoted as saying “It will offer the prospect of rail and maybe road links from the south-west of England to South Wales. It could even carry a potential Channel Tunnel rail link.” (ICWales, Oct 07). Still there are massive hurdles to jump. The Sustainable Energy Commission concluded in their study that there is a “strong case” for the controversial barrage but only if it is a public project which complies with environmental laws (SD Commission July 07).

What are the Costs?

Before construction can start, the project has to clear planning hurdles and about fifteen billion pounds in funding must be found. The Commission’s support is also largely dependent on the creation of thousands of hectares of alternative habitat for wildlife around the estuary (SD Commission July 07).
After an initial investment for a generation plant the costs of electricity produced is one of the biggest deciding factors in choosing which technology is the best to use. As can be seen in the graph below coal gas and nuclear are far cheaper alternatives to wind farms and wave generation (Royal Academy of Engineers March 04). Costs are from as little as 2.2 pence per Kwhour to 3.2 pence per Kwhour. Far cheaper than the renewable sources the cheapest being 5.4 pence per Kwhour and going as high as 7.2 pence per Kwhour. The main reason that these renewables can compete is that you have to consider the cost of carbon dioxide emission which pushes up costs of fossil fuel generators as far as 5.2 pence per Kwhour, although nuclear stays unchanged at 2.3 pence per Kwhour. On this basis both barrage and lagoons are very competitive. The barrage is projected to be capable of producing electricity at a cost of 5.5 pence per Kwhour (Friends of The Earth, Jan 04). This puts it well within the renewable generation cost bracket and far below the offshore generators. The lagoon on the other hand is far cheaper with projected costs of as little as 2 pence per Kwhour(Friends of The Earth, Jan 04). This would put its electricity cost below that of nuclear generation making it a very financially viable project.

So what is going to happen?

It is quite apparent that something needs to be done about climate change and renewable energy sources need to be seriously considered. Action needs to be taken now to preserve our future. Sustainable technologies are the clear way forward in the future. Many sustainable technologies are expensive to implement and are uneconomical to run without government funding and support. Both wave generation and on and offshore wind farms cost more to run than current fossil fuel fired power stations and so their electricity is more expensive. This means that it is hard for them to compete in the electricity market. The proposed barrage comes in at a similar price to its fossil fuelled competitors making it viable and the lagoons are even cheaper making both of them very attractive projects. The lagoons, if they perform as they are predicted to are far better than the currently proposed barrage as they can produce large amounts of electricity cheaper and with less environmental damage.

References

Friends of The Earth, Report, January 2004, A Severn barrage or tidal lagoons? A comparison, Retrieved 20th October 2007 from http://www.foe.co.uk/resource/briefings/severn_barrage_lagoons.pdf

Sustainable development commission. July 2007. Tidal Power in the UK Research Report 3 – Review of the Severn Barrage proposals Final Report. Retrieved 20th October 2007 from http://www.sd-commission.org.uk/publications/downloads/tidalpoweruk3-severn_barrage_proposals.pdf

ICWales, News Report, 2nd October 2007. Hain backs Barrage plan by David Williamson, Retrieved 22nd December 2007 from http://icwales.icnetwork.co.uk/news/tm_headline=hain-backs-barrage-plan&method=full&objectid=19878996&siteid=50082-name_page.html

ICWales, News Report, 11th April 2006. It’s time to consider a Severn barrage by Tomas Livingstone Retrieved 22nd December 2007 from http://icwales.icnetwork.co.uk/news/feature-news/tm_objectid=16929474&method=full&siteid=50082&headline=-it-s-time-to-consider-a--severn-barrage-name_page.html

BBC News report 23rd May 2007, Tidal barrage moves a step closer, by Anonymous Retrieved 2nd January 2008 from http://news.bbc.co.uk/1/low/wales/6681113.stm

R-Energy Report, A report on current technology that may affect Severn Estuary barrage proposals retrieved 2nd January 2008 http://r-energy.co.uk/lagoon.html

Department for Business Enterprise & regulatory Reform, S J Taylor. Final Report: January 2002. ETSU Report No. T/o9/00212/00/REP. The Severn Barrage – Definition study for new appraisal of the project. Retrieve 9th November 2007. From www.berr.gov.uk/files/file15363.pdf

The Royal Academy of Engineers, Report March 2004, The Cost of Generating Electricity a commentary. Retrieved 22nd December 2007 http://www.raeng.org.uk/news/publications/list/reports/Cost_Generation_Commentary.pdf

Thorpe, T.W., (2002); Swansea Bay Tidal Scheme, AEA Technology plc, http://tidalelectric.com/id24.html).

Parliamentary Office of Science & Technology, February 2007, Postnote Number 280, Electricity in the UK. Retrieved 9th November 2007 from http://www.iop.org/activity/policy/publications/file_21079.pdf.

http://www.treehugger.com. Nd. Severn Barrage divides UK Environmentalists. Retrieved 30th October 2007

www.rise.org.au/info/Tech/tidal/index.html nd. Generating Electricity from the Tide Retrieved 3rd January 2008