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Introduction
In 1997 the costs of deployment of marine energy capture devices was seen as economically prohibitive to commercial deployment due to marginal unit energy cost in relation to conventional fossil fuel energy costs at the time (1). However over the past 10 years with a significant increase in fossil fuel costs and drives towards minimising CO2 emissions, design, development & optimisation of marine renewable technologies and governmental development funds are making marine deployment increasingly economically viable.
Early stage economical design optimisation techniques were developed,
using cost performance functions taking into account interdependent
components, their costs, sizes and performance relationships.
The most significant cost being installation mechanisms, drive
train, power train and rotor blade sizes where applicable. It
was noted that this optimisation was critical to making technology
economically viable. These functions however are not linearly
dependant, incorporating “off the shelf”, “one
off” components and modular design, requiring the resultant
curves to be smoothed to enable economic analysis. Alternatively,
considering the complexity of interdependence of some devices
an iterative optimisation approach would give broader optimum
results, rather than a local optimum in the used data range. This
is the basis of current parametric techno-economic models currently
used by marine device developers.
Current Economic Climate
Current estimates rate the potential market size for marine generation to be a sizable 15-20% of the UK electricity demand (2). This is an approximate figure as technological development and optimisation is yet to decide energy extraction potential. Initial tidal farms are expected to generate power in the range of 9p-18p/kWh, which is currently marginally commercially uncompetitive.
However current devices are limited by scales of economy and associated
prototype development costs. Specific areas of future cost reduction
suggested (2, 3) will come by long term learning
and development of 10-15%, of concept designs, production, construction,
installation and maintenance techniques.
Numerous concepts such as marine current turbines, darrieus turbines,
ducted turbines, counter rotating turbines, oscillating hydrofoils
of differing mooring structures are all in various stages of development
and testing with no significant market leader at present. One
off prototype devices currently being developed are being installed
at costs ranging from £4800 - £10,000/Kw (4,
5). Prototypes by their nature are governed by high development
cost due to testing and design optimisation. Installation costs
are high as no specialist deployment vessels exist with developers
mobilising & using retrofitted Jack up and Strand Jack barges,
at inflated rental costs. These in turn limit the depths of deployment
and consequently device size & power output. Current largest
barges available in the UK operate to maximum depths of 30 metres
(6). Devices with minimal ballast based mooring,
are cheaper to install, decommission and will have a lesser environmental
impact overall. Existing prototypes while giving valuable information
regards power extraction and development of industry knowledge
and techniques, they give inflated costs indication of commercial
development.
A greater indication and understanding of future costs will come
with the first tidal farms being developed and dissemination of
industrial data. Implementing lessons learnt from phase 1 prototype
development, large scale production of full scale devices. This
will further take into account cost with efficient purpose built
deployment vessels enabling more devices to be deployed to deeper
depths and shorter installation times. Understanding of maintenance
scheduling with site specific tidal regimes will also minimise
relative energy lost and cost during device down time.
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Power-cost optimisation
In conjunction with parametric device modelling, further research
and understanding of environmental limits to site specific tidal
power extraction will dictate device power–cost optimisation;
the device size limit to which energy can be profitably extracted.
In the wind industry experience has proven that wind farms with
large rotor diameters at relatively small spacing spheres of influence,
are economically and electrically more profitable. In the marine
industry packing densities and blockage effects have greater influence
than that in the wind sector. Therefore farms of numerous relatively
small MEC devices with minimal blockage effects may prove to be
more profitable, than fewer larger scale devices with higher power
extraction and significant blockage effects. This extraction philosophy
would keep average tidal velocities, available energy extraction
and potentially profits higher while minimising farm size and
environmental impacts.
References
| 1 | BRYDEN, I.G., et al., Matching Tidal Current Plants to Local Flow Conditions. Energy (Oxford), 1998. 23(9): p. 699-709. |
| 2 | CALLAGHAN, J. and BOUD, R., The Carbon Trust: Future Marine Energy - Results of the Marine Energy Challenge: Cost Competitiveness and Growth of Wave and Tidal Stream Energy. [PDF] 2006 [cited 02 May 2006]; Available from http://www.thecarbontrust.co.uk/carbontrust/about/publications/FutureMarineEnergy.pdf |
| 3 | HAUG, M., IEA: Experience Curves for Energy Technology Policy: Iea Engagement and Future Challenges. [PDF] 2003 [cited 02 May 2006] |
| 4 | THAKE, J., DTI Renewables: Development, Installation and Testing of a Large Scale Tidal Current Turbine. [PDF] 2005 [cited 02 May 2006]; Available from http://www.dti.gov.uk/renewables/publications/pdfs/t060021rep.pdf |
| 5 | DTI, The Engineering Business: Stingray Tidal Stream Energy Device Phase 3 [ETSU T/06/00230/00/00; URN No 05/864]. [PDF] 2005 [cited 02 May 2006]; Available from http://www.dti.gov.uk/renewables/publications/pdfs/T00211.pdf |
| 6 | Seacore Ltd. [Webpage] [cited 02 May 2006]; Available from http://www.seacore.co.uk/ |
| 7 | Scottish Enterprise: Marine Renewable (Wave and Tidal) Opportunity Review. [PDF] 2005 [cited 02 May 2006]; Available from http://www.scottish-enterprise.com/publications/marine_renewable_opportunity_review.pdf |
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