When you said the end there I had a crazy thought: use the waves and tides to lift the heavy weight of a gravity battery up a pole that is a like a ratchet so that when it’s lifted it keeps stepping up the pole and doesn’t slide back down. When it reaches the top of the pole it can have an automatic release and drop to the ground. While it drops it will generate electricity. This can be fed to the grid or charge a battery. If you created a farm of these it would work day and night and the different gravity generators would rise and fall in a steady but randomized way that would be consistent on the average.