NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Assessment of Ireland’s Tidal Current Energy Resource
David Fallon and Dr Stephen Nash
Civil Engineering (and Ryan Institute), College of Engineering & Informatics, NUI Galway,
david.fallon@nuigalway.ie; stephen.nash@nuigalway.ie
Abstract
In 2008, fossil fuels accounted for 96% of Ireland’s
primary energy demand of which 95% were imported
[1]. Careful exploitation of Ireland’s indigenous
renewable energy resources is required to help curtail
this over-reliance on imported fossil fuels and to reduce
greenhouse gas emissions. Tidal currents represent a
substantial indigenous energy resource that is both
sustainable and predictable. The accessible tidal
current energy resource has previously been estimated
at 2.63 TWh/y [2].
1. Introduction
The most recent assessment of Ireland’s tidal current
energy resource (SEI, 2004) requires updating. This
assessment used the ‘farm method’ which has since
been shown to over-estimate the tidal current resource
as it ignores the effects of energy extraction. In
addition, turbine technology has progressed
significantly in the intervening years. This research
aims to produce a more accurate assessment of Ireland’s
tidal current energy resource by incorporating the
effects of energy extraction by modern turbines in a
multi-scale nested model of Irish coastal waters.
2. Aims and Objectives
The primary objective of the research is to develop a
nested model of Irish coastal waters using a 2-D depth
integrated numerical model (DIVAST). Optimisation of
nested boundary conditions will then be explored to
develop a more efficient and accurate transition from
the low resolution parent domain to the highly-resolved
nested domains. Once the nested model is developed
the resource will be assessed and suitable locations will
be identified. Resource maps and an online GIS
database will subsequently be generated upon
completion of the resource assessment. Finally, the
research will attempt to develop a methodology to
determine extraction capacities using a rating system
that incorporates the hydro-environmental impacts of
energy extraction and different turbine categories.
3. Most Recent Assessment
The 2004 assessment (SEI, 2004) applied the farm
method to the results of a2-D depth integrated model
developed by RPS Kirk McClure Morton. A grid
spacing of 405m was employed (Figure 1) and further
detailed modeling was carried out at selected suitable
sites with grid spacing’s of 135m and 45m respectively.
The results were validated using tidal height & current
meter data.
20
Figure 1 Depth averaged peak spring tidal currents (SEI, 2004)
4. Methodology
The most recent resource assessment adopted the
farm method. A major problem associated with the farm
approach is that extraction affects the available resource
but this method ignores extraction effects, therefore, the
farm method is not valid.
This research will combine the farm method with the
flux method to provide a more realistic and accurate
assessment of the resource. Kinetic energy fluxes within
the tidal stream will be effectively reduced due to
energy conversion, support structure drag effects and by
the slower moving water in the turbines wake merging
with the faster stream tube. The flux method
incorporates such effects of energy extraction on the
tidal currents.
5. Conclusion
The use of high resolution nested grids and the
incorporation of the effects of power extraction using
modern turbine performance characteristics will result
in a more accurate quantification of Ireland’s tidal
current energy resource.
6. References
[1] SEI (2009) Energy in Ireland Key Statistics. Sustainable
Energy Ireland, Dublin.
[2] SEI (2004) Tidal and current energy resources in Ireland.
Sustainable Energy Ireland, Dublin