The capital cost of marine renewables technologies can be broken down into: the cost of the generation device itself (materials, components and labour in manufacturing and fabrication processes); the costs associated with installing it (deployment); the costs of keeping it on station (foundations or moorings); and the costs of connecting it to the grid (electrical cables and switchgear).
Parameters that Affect Capital Costs
Costs for commercial ocean energy plants are, as for most renewable energy generating technologies, heavily weighted towards up-front capital. The major influences on cost for a particular site are discussed below:
Design Current Speed: The design current speed is the maximum velocity of the water expected to occur at the site.
Velocity Distribution: As the rated velocity of the device increases, so do power train costs. Since the velocity distribution tails off at higher velocities, the capital cost for equipment to extract incrementally more flow power at high velocities may not be “paid back” by the additional power generated.
Seabed Composition: The seabed composition at the site has a major impact on the foundation design of the tidal stream device.
Number of Installed Units: The number of devices deployed has a major influence on the resulting cost of energy. In general, a larger number of units will result in lower cost of electricity due to economies of scale. There are several reasons and these are outlined below:
- Infrastructure cost required to interconnect the devices to the electric grid can be shared and therefore their cost per unit of electricity produced is lower.
- Installation cost per turbine is lower because mobilization cost can be shared between multiple devices. It is also apparent that the installation of the first unit is more expensive then subsequent units as the installation contractor is able to increase their operational efficiency.
- Capital cost per turbine is lower because manufacturing of multiple devices will result in reduction of cost.
Device Reliability and O&M Procedures: The device component reliability directly impacts to operation and maintenance cost of a device. It is important to understand that it is not only the component that needs to be replaced, but that the actual operation required to recover the component can dominate the cost.
Insurance Cost: The insurance cost can vary greatly depending on what the project risks are. This is an area of uncertainty, especially considering the novelty of the technologies used and the likely lack of specific standards. A commercial farm will incur insurance costs similar to mature an offshore project which is typically at about 1.5% of installed cost.
Given below is a list of cost centers and cost drivers for wave energy
Cost Centers and Cost Drivers for Wave Energy
Mechanical and Electrical Cost
Material Cost, Extreme loads
Rating of the machine (installed capacity)
Water depth, tidal range, tidal flow, storm conditions and compliance
Type and availability of vessels required, distance to port, time taken for installation and weather.
Power transmission level and distance to shore
Management, insurance and permissions
Cost of replacement parts, component design duty and known service intervals, time to complete service, distance to port and weather
Cost of replacement parts and spares, weather and cost of personnel and material standby
(Source: CarbonTrust, Cost Estimation Methodology, May 2006)
Capital Costs for Tidal Energy
Most research in tidal energy systems is happening in the domain of tidal streams.
Breakdown of Capital Cost for a Tidal Stream FarmSource: Carbon Trust
A Sample Capex Breakup Data for a 50 MW Tidal Stream Project
% of total
Power Conversion System
Structural Steel Elements
Subsea Cable Cost
Subsea Cable Installation
Onshore Electric Grid
Total capex ($/Kw) 2750
1. Power conversion system cost includes all elements required to go from fluid power to electrical power suitable to interconnect to the tidal stream device. It includes rotor blades, speed increaser, generator, grid synchronization and step-up transformer.
2. Structural steel elements include all elements required to hold the turbine in place.
3. Subsea cable cost includes the cable cost to collect the electricity from the turbines and bring the electricity to shore at a suitable location.
4. Turbine installation cost includes all cost components to install the turbines.
5. Subsea cable installation cost includes, trenching, cable laying, and trench back-fill using a derrick barge. It also includes cable landing costs.
6. Onshore electrical grid interconnection includes all cost components required to bring the power to the next substation.Operations & Maintenance CostsThe O&M (Operation and Maintenance) costs of marine renewables can also be considered in several parts, including: maintenance, both planned and unplanned; overhauls; where it is most economic to re-fit components during the service life; licences and insurance to allow the devices to be kept on station and to manage the associated risks; and ongoing monitoring of wave or tidal conditions and the performance of devices.
Operating costs also need to take into account insurance costs, which is usually about 1-1.5% of total installed capital cost.