Both hydroelectric and tidal energy, often called wave energy, work in a similar way. These energy sources use large dams or barrages that prevent water from flowing through, as it normally would. This results in a water imbalance on both sides, with one side having a much higher level of water than the other side.
The difference between the two renewable energy sources is how the water causes an imbalance in water levels.
In a hydroelectric dam, water flowing from upstream is trapped. Trapping this water for a while eventually forms a reservoir, which is essentially a large lake that stores water.
When released, the potential energy from the water’s descent is converted to mechanical energy as it turns turbines, which then generate electricity.
Tidal barrages use tides, which are the regular rise and fall of sea levels, mainly due to the effect of the Moon’s gravity. A tidal barrage is built over an estuary, which is the point at which the river meets the ocean.
We can close the gates on the barrage to trap the water as the tide comes in. When the tide begins to go out and there’s enough of a height difference between the water level inside the estuary and the sea outside, water is released through turbines in the barrage.
As water flows through these turbines, electricity is generated.
Wave machines use the kinetic energy in the movement of waves to drive electricity generators.
Both hydroelectric dams and tidal barrages exploit the difference in water levels to generate electricity. This differential means that stored water has a large amount of gravitational potential energy that gets transferred to kinetic energy.
The kinetic energy from the moving water turns the turbines. Those turbines are connected to generators which generate electricity as the turbines spin. This water then flows through to the other side.