Another form of hydroelectricity being investigated involves the movement of the ocean. Here, consistency could mean the difference between wave power or tide power.

Like the wind that drives them, ocean waves are intermittent. Thus, any wave power generators that have been developed suffer from the same problems that on- and off-shore wind power generators suffer from. Solar power generators also suffer from this problem of intermittency, but still generate some power on even cloudy days. In order to keep a stable energy supply, backup power systems are used, but also need to be backed up by a more steady source, typically fossil-fuel driven, which defeats the purpose of renewable energy.

On the other hand, certain types of ocean energy aren’t as finicky, and researchers are now looking to the moon to determine when the best energy is going to be produced. Because the Earth rotates on its axis every 24 hours, the moon’s gravity pulls on the ocean only when it is over that part of the ocean. Because high tide comes every twelve hours or so and low tide in the between, tidal generators can generate electricity every six hours, both when the tide is coming in and going out, minus the time when the tidal flow is reversing between high and low tides.

Recently, a new 1MW tidal turbine off the coast of Sweden was installed to test its ability to generate electricity from ocean energy in the tide. It has a 59ft rotor sweep, is buoyant for easy transport, has adjustable rotor pitch to manage the load, and even steers into the tide flow for maximum efficiency. Testing will continue for an 18 month period that started in March.