For MHK Technologies
IEC design standards for MHK plants are under development. However, information required for MHK device design and installation overlaps with that required for wind plants. The same phenomena that create loads and foundation stresses for wind plant structures also do so for MHK systems. Two differences between wind plant and MHK facility design information requirements are the effects that winds and currents have on these respective devices.
A few items worth noting for MHK devices are the existing Det Norske Veritas wave and tidal energy device certification standards,7 which use 100-year wind and 10-year current, as well as wave, wind, and current direction, to determine mooring standards. Furthermore, Sandia National Laboratory is carrying out a 50- and 100-year extreme wave analysis using data from three NDBC/Coastal Data Information Program (CDIP) buoys from the coast of northwestern California. The results of this analysis were not complete at the time of this report.
Near-Surface Wind Velocity
The loading on a wind turbine largely arises from hub height winds impinging on the rotor, while MHK devices with a superstructure are mainly affected by near-surface winds. Observations or validated numerical simulations of these near-surface winds are needed just as they are needed for hub-height winds in wind energy applications. However, MHK applications have the advantage of not requiring extrapolation of wind speed measurements.
Currents
In the same way that wind shear and atmospheric turbulence are important design conditions for wind turbines, current shear and subsurface turbulence are especially important for MHK devices that extract energy from both tidal and open-ocean currents. As noted, technology exists to provide these measurements, but observations at any particular location are unlikely to be available.