- The primary advantage of tidal stream technology is its predictability, renewable status and
- Marine current technology has proven baseload potential. Using some of the power to meet peaks in demand
may prove even more economic.
- Although immature, this energy resource offers great promise in terms of
energy yield, socio
economic benefits and emissions savings.
Summary of findings - the three Es
The three Es represent Energy, Economics
and Environment. These have been an integral consideration
throughout this project:
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- Scotland has an abundant Marine Current energy resource, powered by the strong tidal
currents experienced around the Scottish coastline (for further details of sites please
refer to Resource Basics section).
Due to the distribution of the locations with sufficient tidal velocity, combining
the power output from multiple sites produced a variable combined output. In order to
supply a flat power output that could satisfy baseload demand, a storage technique was necessary
to ‘fill in the gaps’.
The energy supplied from the baseload supply strategy was limited. The large range in
tidal speeds experienced between Spring and Neaps tides results in an unavoidably
variable source of energy. The variation in power generated between
Spring and Neaps can be very large - the biggest constraint to providing baseload.
For a constant flat baseload, the size that can
be supplied is limited by the amount of energy generated during Neap tides, as no long-term
storage technology is available to generate additional energy over the 14-day
Springs-Neap tidal cycle required to fill in the shortfall experienced at Neap tides,(e.g.
Cruachan is limited operating at 400MW for 22 hours).
Developers will need to consider whether to install just enough capacity to generate to the
energy level limited by neaps (smaller capital costs) or if they should
install more capacity (turbines with higher rated speeds) to exploit the full resource
during Springs as well as neaps (resulting in a variation in the baseload). In practice,
individual schemes will likely be developed with the aim of maximising the energy
generated and not compromise energy generation for the collective purpose of supplying baseload.
The size of baseload potentially available would be limited by the pumped
storage capacity available. It was observed that increases in the energy generated from
the larger MCT sites would result in a larger variation in the overall output, requiring large
amounts of excess energy to be stored.
- The minimum storage supply strategy required 164.0 MW/h per day of pumped generation to
provide a 433.5MW baseload
- The maximum storage supply strategy generated 4463.43 MW/h per day from pumped storage
plant to supply 881MWs of baseload.
Availability of storage plant may
restrict baseload supply. Storing energy generated from the MCT schemes at times of peak
demand may be impractical as Cruachan will be generating to meet the demand. Conflicts with
other users of Cruachan were also not addressed in this study.
There may be alternatives to using pumped storage to provide a constant energy supply which should
be considered. For example, an alternative to using Cruachan, could be to implement a coordinated
supply policy working together with the Hydro industry in Scotland to provide the additional
generation and storage required.
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This project set out to prove that marine current energy could be used to meet a constant
proportion of Scotland's baseload electricity supply through phasing of geographically
It has been shown that this is possible, but that this may be an impractical
and uneconomic use of this abundant resource.
Transportation of power to pumped storage to
enable a constant baseload to be supplied, would involve several potentially uneconomic
As the tide works to a 12.4 cycle on average, the times at which excess energy is stored would
change from day–to-day. Storing energy at times of peak demand, for example around 6pm on a weekday,
would be uneconomic because the revenue made from selling this energy to the grid would
be much greater than if it were stored, regenerated and sold later.
From the perspective of the Pumped Storage business, it would be uneconomic to recharge
during peak demand periods, so from this perspective storage of excess energy may be restricted to
A more economically viable strategy
may be to supply a variable yet entirely predictable source of energy which may still be
used to meet as proportion of Scotland’s baseload in conjunction with
other more flexible energy sources. This would replace the requirement for storage and eliminate
all the expensive practices that go with it .
- Alternatively, the baseload proportion supplied could be altered on a weekly or monthly
basis to allow an amount of the peak power to be used to meet peak demand, depending upon the
match of supply and demand profile predictions at this point in time.
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No major Environmental Impact Assessment of this technology has be carried out, therefore the
ecological and environmental effects are difficult to quantify in exact terms.
However, a large-scale MCT supply strategy involving installed capacity of sizes comparable
to this study (up to approximately 1800MW) would undoubtedly have significant negative impact
on the local seabed and marine life.
A large scale development would also run in to major opposition from existing users such as
fisherman, the military, commercial shipping and recreational users. This could raise many
conflicts during planning.
- Large scale generation would result in significant savings in CO2, SOx, and NOx
emissions due to large amounts of existing thermal generation that would be replaced such as
Combined-Cycle Gas Turbines (CCGT) and Coal-fired power stations. Such measures would help the
UK government meet it’s target of reducing CO2 emission levels by 50% by 2050.
The localised negative effects on the environment and ecosystem could be considered
insignificant when compared to the major global benefits through cutting emissions,
helping to reduce the greenhouse effect and global warming.