OES Annual Report 2012 - Ocean Energy Systems

125
05 / DEVELOPMENT OF THE INTERNATIONAL
OCEAN ENERGY INDUSTRY: PERFORMANCE
IMPROVEMENTS AND COST REDUCTIONS
RENEWABLE POWER SOURCE
Wind Power per m 2 of input wind at 12m/s
(typical rated velocity of an offshore wind turbine)
POWER DENSITY
1,100 W
Tidal Power per m 2 of input water current at 2.4m/s (typical rated
velocity of a tidal turbine to achieve >30% capacity factors)
Wave Energy flux per m 2 of seastate Hs = 6m, T z = 8s
sea state (typical rated sea state for wave energy converters
to achieve >30% capacity factors)
7,000 W
9,400 W
(average in upper 10m of sea)
TABLE 8: Power Flux from different renewable sources of power through a vertical 1m 2 reference area. Reference wind velocity, current
velocity and sea state are chosen as typical rated values that would be sufficient to achieve capacity factors of >30% at suitable sites.
most part, more subjective than that of TRLs. ESB believe that technology developers will have a firmer
understanding of costs and performance once TRL8 is achieved. In the meantime, there are other cost
indicators which may be used to inform economic competitiveness. These ‘cost indicators’ at a pre TRL7
phase include:
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Tons of steel per MW
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Ì Wetted surface area and working surface area (e.g. blade area, rotor swept area, and float size)
Ì Foundation or mooring concept
Ì Mechanical complexity of overall system and PTO
Ì MW rating for single unit
Ì Type of WEC and PTO
Ì Construction, installation, and maintenance concepts
Other than the basic costs of the converter hardware itself there are other cost risks to projects which are
outlined briefly below. If the focus is solely on reducing the cost of wave or tidal energy converters, design
changes could introduce other non-core cost risks to a project. These risks include;
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Device rating – Most wave and tidal energy converters are currently rated at around 1MW. By increasing
the MW rating of devices, there can be a significant reduction in other parts of the Capex such as electrical
infrastructure, installation and foundations/moorings, consistent with the experience of offshore wind. Also
increasing the unit rating may reduce the Capex per MW of the converter itself, although this has remained
relatively constant for offshore wind.
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Capacity factor – The capacity factor has a direct impact on the productivity per MW installed and this is
reflected clearly in acceptable cost and performance envelopes (Tables 1-3). However, the electrical system
must also be rated for the maximum output power and a lower capacity factor means a low utilisation of
this expensive infrastructure. Low capacity factors can result in significantly increased downstream per MW
infrastructure costs. In wind energy, optimal capacity factors are higher than for onshore wind as a result of
the cost of offshore electrical balance of plant (35-40% offshore as opposed to 25-30% onshore).
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Insurance – Insurance is a critical part of the viability of a project and it is likely that in early stage wave
and tidal farms this will contribute significantly to Opex. In-service data, certification, and warrantees will
go some way towards reducing the insurance costs and managing the safety critical risks to the satisfaction
of utility investors.
Conclusions and Perspective
The above assessment shows a challenging but realistic view of the market for ocean energy. In some jurisdictions
the market conditions exist to allow investment in pre-commercial Phase 1 small array projects. These projects
will begin the process along the cost reduction trajectory presented. Supplementing offshore wind with wave or
tidal stream energy as large scale sources of renewable generation will only occur when costs are competitive.
ESB believe that ocean energy can develop towards sustainable and competitive projects. This trajectory is
achievable, based on economies of scale and learning rates, but consistent supports and long term policy are