Cost Comparison and Analysis

Fig. 4: Predicted future costs for a proposed tidal current turbine in the UK (P. Fraenkel, 2004).

Figure 4 shows the estimated future cost per kWh for a tidal current turbine system currently under development in the UK in pence per kWh. It shows rapidly declining costs in the early development stages before leveling off and reaching a limit of between 3 - 5 p/kWh. This translates to $0.05 - $0.08/kWh which is just slightly more expensive than the $0.05 - $0.06/kWh cost of coal (currently the most common source of electricity generation). However, the cost per kWh associated with tidal current technology is harder to predict as it will change depending on the location of the generating system. Obviously, more favorable conditions will be able to generate electricity more cheaply and efficiently. Also, the site will affect associated installation and maintenance costs.

The lifetime of a tidal turbine may be extrapolated from current offshore platforms (Li & Florig, 2006). Offshore platforms typically achieve lifetimes of about 20 - 30 years; however, accurate estimations of operational lifetimes will not be available until more full-scale generation systems are developed (Li & Florig, 2006). Despite this lack of experience, these optimistic estimates come from the fact that pre-commercial testing of near-shore units have resulted in turbines operating without failure over a 5-year period with minimal maintenance (Li & Florig, 2006).

Operating and maintenance costs associated with a tidal turbine farm are affected by a number of factors such as the size of the turbine farm, location, the layout of the turbine farm, and the efficiency at which electricity can be generated (often a function of local conditions) (Li & Florig, 2006). A closely-spaced layout will make make maintenance easier by exposing less cable and reducing travel time by boat between turbines, but will reduce the efficiency of the turbines due to wake effects between the adjacent turbines; conversely, maintenance costs will increase as the spacing of tidal current turbines increases due to the increase in exposed cables and distance between turbines, but the efficiency of the turbines is increased due to decreased wake interactions (Li & Florig, 2006). Figures 5 and 6 show predicted O&M costs for a hypothetical tidal current turbine farm Seymour Narrow, British Columbia and off the Northeast coast of the US respectively for various turbine farm sizes.

Fig. 5: Annual projected O&M costs for a hypothetical Canadian turbine farm (Li & Florig, 2006).

Fig. 6: Annual projected O&M costs for a hypothetical American tidal turbine farm (Li & Florig, 2006).

In both cases depicted above, a small farm is 30 turbines, a medium farm is 50 turbines, and a large farm is 100 turbines. The estimated O&M costs vary greatly due to the differing efficiencies of energy extraction associated with each location (Li & Florig, 2006).. Seymour Narrow is one of the best locations for a tidal turbine farm in North America due to high current speeds; however, a large farm would not fit in the limited area of the location. Projected O&M costs for the Northeast US are higher because higher winds and more challenging wave conditions associated with this location would make maintenance trips more difficult and, consequently, more expensive. Additionally, lower current speeds would also drive up O&M costs due to decreased turbine efficiencies (Li & Florig, 2006). These figures indicate that the cost per kWh can be optimized by siting and sizing tidal turbine farms in the most efficient locations possible.