(Images via: OceanWorld, CNN, HIE and Geekologie)
(Advantages of &) How Ocean Tidal Power Works
Tidal power is in many cases the lowest-impact but also the most reliable form of taking energy from water. Because it relies on repetitive lunar cycles, unlike wind or solar power, a tidal power station (aka tidal farm) can be relied upon to produce a predictable amount of energy. Also, since most tidal power generators sit below the surface of the water they are not obstacles or eyesores to humans but can impact ecosystems.
(Advantages of &) How Surface Wave Power Works
Like tidal power, wave power generates energy energy primarily from large open bodies of water (seas and oceans) using an array of machines that individually harness the kinetic energy around them. Water power stations (or parks) take advantage of the elliptical motion of surface waves to drive pistons and convert the power around them into electrical energy. They are also relatively inexpensive to build and deploy.
(Advantages of &) How Hydroelectric Power Works
Unlike tidal and wave power, hydroelectric power relies on gravity that naturally pulls water from one level to another – often around artificial or natural waterfalls in large rivers. Though they range in size and type they work primarily on the same principles: water passes through with force which rotates a series of turbines that in turn generate renewable alternative which can be used for all kinds of purposes.