Water Energy Solutions - The Lowdown

Wave Energy
The wave action of the oceans can provide clean energy in the same way that wind turbines do. Here’s how it works: you have a chamber with a turbine, and whenever a wave pushes into the chamber it pushes the air out which turns the turbine which is attached to a generator. An alternative method is to have a piston which is directly attached to a generator, and the wave motion moves the piston.
Although wave energy is an efficient way to produce energy, simply due to the abundance of waves, it has not become as popular as wind energy.

Tidal Energy
Tidal energy works by building a dam to trap the water as it rises with high tide. Then once then tide has dropped, the water is let out from the dam and the motion of the water flowing out is used to turn turbines which are attached to generators.
Tidal energy is very efficient if you compare it to coal – 85% versus 30%. However, in order to achieve this efficiency, there are strict conditions which must be met, such as the tidal range being at least 7 meters. Also, it is very expensive to set up a tidal power plant, and there are not very many countries that have them.

OTEC (Ocean Thermal Energy Conversion)
OTEC involves using the difference in temperature in large bodies of water to generator power. In order to do this, the temperature difference needs to be 38 degrees or more. Closed-cycle OTEC system use a liquid that has a low boiling point (e.g. ammonia) to turn a turbine. Open-cycle OTEC systems make use of the warm temperature of surface water. This is done by putting warm seawater into a low pressure container, which makes it boil.
OTEC has not yet become a popular form of energy generation as it is still considered an emerging technology.

Osmotic Power
This is a method of generating electricity by making use of the difference between freshwater and saltwater. A typical situation where freshwater meets saltwater is where a river meets the sea. By placing a semi-permeable membrane between the two types of water, the salt will pull the freshwater through the membrane, thereby creating pressure on the saltwater side of the membrane which can then by used to turn a turbine.
Osmotic power has some great benefits. As well as being clean and renewable, it can be used anywhere where freshwater meets saltwater. Also, it can generate power constantly, regardless of weather or any other factors.