SURVEYOR'S NOTEBOOK

“Sustainable Energy – without the hot air” David J.C. MacKay (1967-2016) – Wave Resource Review

By Michael Raftery

Sustainable Energy – without the hot air is an excellent text covering the various renewable power sources and their potential contribution to the energy supply mainly focused on the United Kingdom.

One statement that I consider to be a significant error is on page 73, where MacKay states “The fetch required to stoke up big waves is thousands of miles.”

Anyone who has lived on the shore of a lake over 20 miles wide for any significant amount of time has seen waves over 3 feet (1 meter) high approach their shore when winds are 22 miles per hour (10 meters per second (10m/s)) or greater. Fetch on the ocean is exactly like fetch on a lake, and once waves are over 1 meter high, they grow rapidly in sustained winds; therefore, his assumption that the available wave resource is dependent on miles of coastline is invalid as sustained winds over the ocean are common.

Wave farms can be placed in continuous rows going offshore for hundreds of miles, spaced at twenty miles, and each wave farm will be harnessing waves over 1 meter-high, in sustained winds of 10m/s or greater, even if each wave farm extracts 100% of the incoming wave power.

Commercially viable wave energy conversion (WEC) systems will have minimum water depths, for safety reasons, and not maximum water depths as mooring systems developed for offshore oil platform systems can be adapted for industrial scale WEC systems.

I truly wish David J.C. MacKay was alive today to discuss the ocean wave resource as his years of work were genuinely a significant contribution to human understanding of sustainable energy systems, or the term I prefer to use, sustainable power systems.