I did my Dissertation on alternate energy. Here are some extracts:
Aims of the project
By 2020 the UK government has agreed to produce 20% of UK energy usage from renewable energy sources. If the UK are to solely use wind power to meet the EU Renewables Objective, then two wind turbines will have to be erected every day until 2020i.Can you image that happening?
This thesis looks into the various renewable energy sources that can be implemented on a small scale to generate enough energy to power the 4000 student accommodation for ‘The Bay’ development proposed by Swansea University.
Climate change
Climate change is a result of the greenhouse effect that has been accelerated through human activities, particularly burning oil and coal. Carbon dioxide (CO2) is a naturally occurring molecule in the atmosphere that along with the other greenhouse gases (GHG) retain the sun’s heat. The increased production of CO2 enhances the effect of climate change, which results in increased temperatures and a heightened risk of extreme weather.
The threat of extreme weather hitting the UK can be daunting as storms and hurricanes will become more frequent damaging property, infrastructure and crops. Estimated cost of major climate-related natural disasters is $200 bni indicating that as a result of our impact on climate change, we are making people more vulnerable to weather related natural disasters. Most governments are taking steps to combat climate change. International initiatives have been introduced, including the Kyoto Protocol, which was brought into action in February 2005 and which sets national legally binding targets to reduce the production of GHG emissions. All developed countries have agreed to reduce GHG emissions by 5.2% below 1990 levels in the period 2008-12.ii The UK took a target of 12.5% reduction by 2012.6
The key to reduce GHG emissions is to minimise the amount of energy consumption by changing our way of life. The main contributor to climate change is energy production for the national grid through combustion of fossil fuels, which releases vast quantities of CO2 into the atmosphere. Spurred on by diminishing reserves of carbon-based fossil fuels, spiralling fuel prices and potential blackouts through political ransom, the government is striving to obtain eco-friendly energy sources that can power the UK for years to come.
According to the Energy White Paper, current nuclear developments are seen to be economically unattractive; there are still ongoing issues of disposing of the nuclear waste that was created a century ago.i
Tidal stream generators
Generally the maximum power of the tide can be harnessed with a small number of turbines if restriction to flow it taken into account. In respect to the drag caused by addition turbines, one would think that adding further turbines to that channel will increase the amount of energy harnessed. This is far from reality as adding too many turbines can decrease the current flow to such an extent that the energy harnessed is reduced.
The maximum power obtainable can be achieved with few turbines, as allowances must be made for the reduction of flow due to the drag of the turbine retaining structures.
Due to the capacity of tidal barrages and lagoons being too great for Swansea University’s relatively small development, I will look into tidal stream generators, as the energy generation is predictable and dependable. Tidal stream turbines need a mean maximum surface velocity at spring tide of about 5 knots (2.5 m/s) or more in order to collect enough energy to be cost-effective, as well as sufficient water depth, preferably 20 to 30 m. 50 miles out from Swansea the water can have depths of 25 m and the spring tide current can be up to 2 m/s as shown in Appendix E.
The SeaGen turbine that I am investigating has technology that is the most advanced in the world, by a significant margin, but it is still at the prototype testing stage in Strangford Narrows. *Future projects probably need to involve arrays of multiple turbines to obtain economies of scale. SeaGen costs, very roughly, are at present £4 - £5 million per megawatt installed depending on project size. Costs are expected to halve by the time 100 or 200 MW of systems have been manufactured and installed.i *Connecting to the grid varies in cost but an estimated figure is at least £1m per km. There are two problems with tidal stream generation in a Swansea area. First the current velocity is less than 2.5 m/s, and because energy is proportional to the cube of the velocity the difference for example between 2.0 and 2.5 m/s is 25% in velocity terms but 95% in terms of energy capture. *In other words a site with 2.5 m/s gets 95% more energy than one at 2 m/s. 3 m/s that can be found off Anglesey represents 330% of the energy at 2 m/s.
The Severn Estuary and Barrage site does not have locations with sufficiently fast currents to make a project with tidal stream technology attractive.
Also, it is unlikely to be worth installing less than about 10 MW worth of turbines in any project because of the high fixed overheads. A 10 MW project at present will cost in the region of £40 million.
Figure 15: Typical variation in output from tidal stream power due to spring-neap cycle
The magnitude of the tidal stream resource (which combines with wind effects to produce currents) varies sinusoidally, with the highest speeds occurring at mid ebb or mid flood, and with speeds approaching zero at the turn of the tide.ii There is also a very large difference between average power outputs during spring versus neap tides, as shown in Figure 15.
Tidal stream (turbine) generators can extract a significant proportion of the power that tidal barrages can produce, but with far less environmental impact. One of the main problems with the proposed Severn barrage is the environmental impact that it will create, including flooding and drying areas such as the tidal mudflats which are home to many rare protected birds.
The use of tidal turbine power generators enables significant power extraction without the implications that arise from large unsightly barrages.
Adding more turbines would increase the power if the tidal current were unaffected. But inevitably an increase in turbines brings an increase in the restriction to tidal flow. More power is available if the channel is long, with a large head (tidal range).
There are basically three options for generating power from tides:
1.exploiting large tidal range in a bay;
2.large tidal range in an estuary with a barrage;
3.strong tidal currents in a channel.
With respect to the River Severn’s estuary there is a small tidal head with strong currents. The energy produced is greatly affected by the flow rate and less on the head. Therefore having too many turbines will have a large detrimental effect on the amount of energy that can be harnessed from the tide due to the drag caused by the turbine supporting structures as shown in Figure 16.
Figure 16: Tidal flow fence diagram
Swansea has a large tidal range; the Bristol Channel has the second largest tidal range in the world9. The current is insufficient to generate adequate power to make installation of a tidal current turbine economically viable.
Aside from tidal current energy generation, the tidal range can be exploited through the use of ‘Tidal lagoons’. Tidal lagoons and tidal barrages still remain an untapped resource that could produce 20% of the UK’s electricity demand within 15 years.iii
Tidal lagoons consist of a ring of rock built up into walls to capture the tides water at high tide. As the tide leaves, the hydroelectric turbines begin to produce energy through the release of the contained seawater. Unlike tidal current and wave technologies that are in their infancy, lagoon solutions have technology available for commercial installation. The main benefit of tidal renewable energy generation is the predictability of electricity production. Tidal lagoons have the ability to release the stored seawater at a required rate depending on energy demand. Knowing the tide timing allows exact electricity production from base load power stations to backup tidal energy production short-fall optimising efficiency over base load support for wind power generation. For example, the unpredictability of wind power insists that the coal or gas fired power stations continually alter production, which is far from efficient. Lagoons can produce energy on the incoming tide as well as the outgoing whereas tidal barrages only generate energy on the ebb tide due to silting.9
Swansea Bay has a mean tidal range of 7 m,iv which makes the bay an excellent location for a tidal lagoon as the Severn Estuary has a cross-section sufficient enough to prevent disturbance of shipping lanes.
The cost of a tidal lagoon is great; installations costs are high due to the many tonnes of material needed. There is a proposed tidal lagoon for Swansea Bay with an expected capacity of 60 MW.v
The UK has a considerable tidal power resource that could be exploited to produce renewable electricity with an output equal to around 10% of UK electricity supply. This illustrates the importance of considering all the options for exploiting this resource. The UK is in a unique position, with a superior tidal stream resource combined with the largest collection of devices being developed or tested anywhere in the world. This UK success story is the product of a number of factors, but the strong leadership shown by the UK Government and the Scottish Government in providing support for marine renewables since 1999 is also an important factor.
Dont mind the singing in the background, it was my classmate being up over 36 hours trying to put the finishing touches on his topic.
not to mention other garbage 