The issue with the various alternative energy sources is that they are intermittent. You can’t trust the sun or the wind to provide a constant power output, and people can do at best is to predict. Ocean currents, on the other hand, are moving steadily, and could provide us with endless amounts of energy while being consistent.
Toshiba, in association with three other organizations: IHI Corp, the University of Tokyo and Mitsui Global Strategic Studies have announced their intention to start developing a system that will harvest the movement of water under the ocean for commercialization purposes.
The new oceanic energy harvesting system will profit from the fact that the output of their machines will be constant. The devices will float under water, so they will not be affected by the weather and/or ships passing nearby.
Then, the twin turbines will rotate in opposite directions, thus cancelling the rotary torques generated by each other, hence both generators will have a stable position. Maintenance will be easy to perform, since the turbines will be easily extracted by adjusting the buoyancy, hence the cost per unit will be drastically lowered compared to other similar systems already in use.
An issue that comes to my mind is the way that the energy will get transported onshore. Among other options, I think the best of them would be to extract hydrogen from the heavily-available water, compress it into high-pressure tanks and have a boat swap the tanks when they fill – that’s just an idea, I really have no clue how they’re going to handle the transport part.