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Break-even Capital Cost for Tidal Generation on a Real Electricity System
turbine with a capital cost of
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experience combined with a small number of moving parts has€680,000/MW installed. Thus, the
benefits of tidal generation are such that the capital costs would resulted in the capital costs of wind turbines falling to a relatively low
have to be dramatically lower than the cheapest conventional unit in level. The operating environment for wind turbines is also much more
order to be economically viable from a system perspective. forgiving on the mechanical parts than the marine environment.
Denny and O’Malley
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found that the break-even capital cost for wind
Other Interesting Issues generation in Ireland is in excess of €1.2million/MW installed.
Omitted in the discussion above were some of the ‘softer’ benefits
of tidal generation, such as the creation of jobs, improvements in The low load factor of tidal is its main downfall in terms of providing
local standard of living, knowledge-building, etc. These benefits are emissions, fuel and capacity savings. As shown previously, the power
difficult to estimate and will vary depending on the location of the output from a tidal turbine will only reach its maximum output
tidal generators. In light of recent economic conditions, the value of during a spring tide, which occurs for a short time twice each
job creation is likely to be significantly greater now than in the past month. Installing a turbine that is rated to capture the spring tide
five years, but the pursuit of renewable deployment with the aim of
increasing employment is unjustified unless the technology is
economically sustainable in the long run.
Although tidal energy is
Another key issue is who bears the costs and who reaps the benefits predictable, its low load factor
associated with tidal generation. It remains an open question as to
implies that it is not necessarily
how many of these costs and benefits would be passed on to the
consumer in the market price. This is particularly pertinent if public
superior to other forms of
funding is utilised to support investment in these technologies.
renewable energy.
It is often publicised that tidal generation is superior to other forms
of renewable generation due to its predictable nature. However, as
discussed previously, the variability of tidal generation can impose may not be economically viable. Developers could improve the load
significant system costs. One approach to reduce the impact on factor of their devices and reduce capital costs at the same time by
system cycling would be to curtail the tidal generation output at installing a turbine with a lower rating that would spill the additional
times of minimum demand. This would reduce the number of starts power during the few days of spring tide each month. This is known
on the system and thereby reduce the impact on the conventional as electrical down-rating (EDR).
units. However, the curtailment of energy from the tidal devices
would have a knock-on effect on the potential emissions and There has been much debate on the visual impact of wind, with
fuel-saving benefits. many considering turbines as a blight on the landscape. In contrast,
tidal generation is much less conspicuous, with the majority of the
Alternatively, electricity storage could be utilised to store the turbine located beneath the water. However, this raises other issues
electricity generated by the tidal device during the night and release for operation and maintenance of the devices. Prototypes have
it at peak times. This would increase the revenues of the tidal already encountered challenges during stormy conditions, not only
generator and would reduce the variability of the tidal output. In with the resilience of the tidal devices but also with the ability of
addition, it is likely that there would be increased emissions and fuel boats to access the devices in rough seas. There are also
savings through a reduction in net demand at peak times. However, considerable technical issues with laying network cables over
constructing a dedicated storage unit to balance the variations in the undulating sea beds that are likely to limit the number of feasible
tidal output comes at a high capital cost. In addition, the combined sites. In addition, when tidal streams are harnessed by TEDs, energy
low load factor of the tidal generation and the round-trip efficiency is taken out of the tide that actually alters the tide. This has a knock-
of storage devices would dramatically reduce the benefits of a on influence on coastal erosion and marine life.
combined tidal and storage system.
In summary, although tidal energy is predictable, its low load factor
It is interesting to note the break-even costs for tidal energy in implies that it is not necessarily superior to other forms of renewable
relation to those of wind. While wind generation has the energy and its low break-even costs suggest that it has a long way
disadvantage of being relatively unpredictable, it has a higher load to go. One must also ask how much of our future energy needs can
factor, resulting in increased energy output and therefore increased tidal energy realistically meet: is it a big fish or a small fish in the
emissions, fuel and capacity benefits. In addition, decades of pool of potential solutions? ■
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Statistics, 2009. Available at: www.ewea.org on the Wind?, 2009. Available at: www.bwea.com grid integrated wind, IEEE Transactions on Power Systems,
/index.php?id=180 5. Lefton S, Besuner P, Grimsrud G, Understand what it 2007;22(2):605–15.
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www.marineturbines.com 41–2. 2009;37:1914–24.
3. Bryans AG, Fox B, Crossley P, O’Malley M, Impact of tidal 6. Denny E, O’Malley M, The Impact of Carbon Prices 9. Commission for Energy Regulation Ireland, Best New
generation on power system operation in Ireland, IEEE on Generation Cycling Costs, Energy Policy, 2009;37: Entrant Price 2007, Report CER/06/148, 2006. Available at:
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