# Tidal power generation

This post’s subject is another way to generate energy from seas and oceans. It is the tidal power generation.

### Where do tides came from?

The tides are periodic variations of sea level. Are caused by Earth’s rotation and gravitational forces of Sun and Moon. This is the equation of gravitational force $F$ between two bodies.

$F=G\frac{m1\cdot m2}{r^{2}}$

• $m1$ and $m2$ are masses of two bodies.
• $r$ is distance between bodies.
• $G$ is gravitational constant whose value is $6,67\times 10^{-11} N\cdot \frac{m^{2}}{kg^{2}}$.

Tide rises in Moon’s direction, but also in Moon’s opposite direction. Because the entire planet is attracted by Moon and force of gravity is lower in opposite side. Influence of Sun’s gravity in tides is lower, although has much more mass, it is much more far away than Moon. During new and full Moon, the three celestial bodies are in same axis and Sun’s gravity force increases Moon’s tide. While in other phases, where Moon is in a perpendicular axis to Sun-Earth axis, Moon’s tide is attenuated.

Tides also contribute to formation of ocean currents which moves underwater turbines. In this post, is shown power plants which use the level difference between tides to turn a turbine.

### Power plant with barrage

It is necessary to build a dam at entrance of a ocean bay or an estuary, forming a reservoir.

This dam must have sluice gates to control water flux and a turbine in the canal to produce electric energy.

The level difference between reservoir and ocean is used to turn the turbine in both sides. Difference between low and high tides must be at least 7 meters to be viable to use as energy source.

### Other forms

Other alternative is build a fence instead of a barrage. In this mode, turbine’s axis are in vertical and are assembled in a structure which reminds a fence. Turbines remind Darrieus type H.

Another form to extract energy from tides is using ocean currents to turn underwater turbines. Because ocean currents are also created by gravitational forces of Sun and Moon. Have already been published a post about this form of generation.

### Limitations of tidal power

This form of renewable energy has the following limitations:

• High installation cost, which decreases competitiveness with other sources.
• Few suitable places for implementation.
• The barrages can cause environmental impact, harming shore ecosystem.
• Tide variation does not always match with consumer`s demand.