The audio on this video explains it. Again, focus on the how calm the sea was. The purpose here was to better illustrate the concept. Imagine moving such a weight (approximately 170 pounds) with a windmill, or with, say, solar power. Waves are far more constant and reliable sources of power. Compare this design with the many others attracting serious venture capital now; it brings exactly the same kind of power ashore where it can be exploited with conventional technology.
March 1 Prototype Video