Wave and Tidal Costs
Capital Costs 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: 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 Cost Centre Main Drivers Capital Cost Structure Cost Mechanical and Electrical Cost Moorings Installation Grid Connection Project Management 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 Operating Cost Planned Maintenance Unplanned Maintenance 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 Farm A Sample Capex Breakup Data for a 50 MW Tidal Stream Project Capex ($/kW) % of total Power Conversion System 830 30 Structural Steel Elements 950 35 Subsea Cable Cost 55 2 Turbine Installation 550 20 Subsea Cable Installation 275 10 Onshore Electric Grid 90 3 Total capex ($/Kw) 2750 Notes: 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. Operating costs also need to take into account insurance costs, which is usually about 1-1.5% of total installed capital cost. 
