2012 05 severn tidal power resource bill cooper, abp mer
TRANSCRIPT
Severn Tidal Power Resource
Bill Cooper
Severn Estuary Forum, Bristol
11 September 2012
A personal, independent and objective view
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Contents
Defining a resource
Establishing a tidal resource
What creates the tidal resource
Harvesting the tidal resource
Major studies
Other resources
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Defining a resource
A natural resource is anything obtained from the environment to satisfy human needs and wants (Wikipedia)
Different types of resource with different values to different users
Local examples of natural resources include:
marine sands for aggregates, cooling waters for power stations, high natural dispersion for outfalls, Severn Bore for surfers, and many others
Energy generation from tidal power is a potential natural and sustainable resource
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Establishing a resource
Theoretical resource – unconstrained top-level estimate of the energy in
the system
Technical resource – the proportion of the theoretical resource that can be
exploited using available technology
Practical resource – the proportion of the technical resource after
consideration of other constraints
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UK Atlas of Marine
Renewable Energy
Theoretical resource
unconstrained top-level
estimate of the energy in
the system
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Establishing a tidal resource
Theoretical resource
Severn Estuary has a good theoretical resource because of:
Very large tidal range; and
Large tidal prism (i.e. the volume of water exchanged by the tide
between high water and low water).
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Establishing a tidal resource
Technical resource
Severn Estuary is most suited to tidal range options relying on low head hydropower generation (i.e. barrages and lagoons)
Form of estuary imposes some engineering constraints on locations
Estuary typically too shallow for present tidal stream technologies in large arrays (no convenient space)
Potential tidal stream opportunities further to the west in the Bristol Channel
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What creates the tidal resource
Large tidal range originates from the open setting of the Bristol Channelfacing a wide continental shelf out to the approaching North Atlantic tide
Distance approximates the resonant condition of a quarter wavelengthof the principal lunar semi-diurnal M2 tidal component
Shelf resonance creates a mean spring tidal range of around 5m for theOuter Bristol Channel
Thereafter, the funnel shaped estuary increases energy density leadingto a mean spring tidal range of around 12m at Avonmouth
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M2 tidal constituent
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Harvesting the tidal resource
Optimising energy capture:
Function of tidal head (range), tidal volume (prism), capacity to install multiple turbines
Maximum mean spring tidal range occurs around The Shoots at 12.3m, coincides with a minimum distance across estuary (4.1km), but lower tidal prism
Mean spring tidal range at Cardiff of 11m, larger distance across estuary (16.1km), but higher tidal prism
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Harvesting the tidal resource
Suggested generating potential:
The Shoots (English Stones), installed capacity of 1.05GW, generating 2.75 TWh per year, with load factor of 30%
Cardiff - Weston, installed capacity of 8.64GW, generating 17.00 TWh per year, with load factor of 22.5%
Conventional fossil fuel power stations operate at around 50% to 65% load factor, new nuclear may be around 90%
Offshore wind typically 35 to 45%
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Major estuary studies
First technical study of the estuary by Professor Gibson (1926 to 1933), based on a physical model
Economic Advisory Council later recommended English Stones scheme with secondary storage basin to increase load factor (to compete with coal power stations)
STPG studies (1984 to 1989) used numerical models, acquired improved primary data
Preferred Cardiff - Weston scheme
DECC Feasibility Study (2008 to 2009) based on improved models, updated engineering considerations, used existing data
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Gibson model
Focussed on the
upstream effects
of tow barrage options
physical model 45ft long
1 in 8,500 horizontal
scale
1 in 100 vertical scale
changed to 1 in 200 to
better represent slopes of
banks
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STPG models
Two models, but different
approach to offshore
boundaries
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DECC Feasibility Study
Two models, same grids
and offshore boundaries
considered both barrage
and lagoon options
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Changes upstream and downstream of any barrage a product of relative position, mode of operation and amount of energy extraction
Upstream changes in the impounded area, more focused and stepped physical change to the system, maximum tidal effects likely to be reduced to present neap tide conditions
Downstream changes unconfined, more dispersed effects over a wider area, but changes in tide also linked to resonant behaviour
Need an appropriate scaled study to consider both upstream and downstream issues
Key effects
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Other resource users
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Other resource users
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Other resource users
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Other resource users
© Paul Williams
