corrosion that is more severe than that experienced by land-based equipment. Corrosion-related problems remain as key challenges for all MHK devices. In addition to the general galvanic corrosion in marine environments, issues related to stress corrosion in both static and dynamic loading environments, corrosion fatigue, biocorrosion, and marine fouling will have to be addressed. Advanced structural materials with appropriate coatings and paints will have to be identified in order to construct the robust, corrosion-resistant components for MHK energy generation (Bahaj and Myers, 2003; Hudson et al, 1980; Liu et al, 1999; Mueller and Baker, 2005). Some technology to address these challenges might be adapted from mature industries like the defense and oil and gas sectors.
Design for survivability becomes another important consideration for device siting, particularly in shallow water. Devices can be destroyed, damaged, or moved from their moorings under the actions of rough seas and breaking waves associated with 50- and 100-year storms that can occur well within the 20- to 30-year life expectancy of the devices. For example, stronger-than-expected currents in New York’s East River caused Verdant Power’s turbine blades to fail only one day after installation in 2006 and led to redesigned blades. Using more rugged design criteria for future MHK devices may drive up the product cost due to exotic materials or increased engineering costs and could also delay deployment until more robust designs are available in the market, all of which may play a role in the cost of electricity generated from an MHK device in the near term. In addition, power electronics on MHK devices will be a challenge to implement and operate reliably.
In addition to the hostile nature of the marine environment, there are other challenges that affect the survivability and maintenance of MHK systems. In shallow tidal and riverine areas, there is a great concern that debris will affect both the efficiency and durability of any installed devices. In Alaska, which is cited as a potentially large resource for development by the in-stream assessment group, river freezing in the winter months and scour incurred during spring ice break-up will make year-round deployment a challenge and may require seasonal device removal. These challenges affect not only installation and maintenance costs and electricity output, but also MHK scalability from small to utility applications.
The basis of many of the critical social, economic, regulatory, and environmental filters identified in previous sections is meeting multiple management objectives from the shared coastal, ocean, and riverine environment. With a growing number of uses, users, and demands, there are