Tidal power is basically a form of hydropower that generates electrical power through the harnessing of the ebb and flow of the tides. Tidal power, despite having great potential, is still not widely used. The working principle of tidal power isn't very complicated: once the tide comes in the water it is stored in the dam, and when the tide goes out the water in the dam is channeled through pipes to turn the blades of a turbine, which then generates electricity.
Tidal power has some important advantages that I should mention. First of all, tidal power is renewable energy source since the tides on our planet are caused by the tidal forces due to gravitational interaction with the Moon and Sun, and the Earth's rotation, which means that tidal power won't get exhausted for at least couple of billion years.
One big advantage that tidal power has over some other renewable energy sources (most notably wind energy) is that tidal power is very reliable energy source. This is because we can predict when tides will be in and out, since rise and fall of tides are much more cyclic than random weather patterns.
Also tidal power produces no greenhouse gases like fossil fuels do, and there is also no waste to worry about like this is the case with nuclear energy. Barrages and small dams needed to harness tidal power can also play very important role in protecting the nearby cities or ship ports from dangerous tides during a storm.
Tidal power is also very efficient energy source, with efficiency of 80%; this means that tidal power's efficiency is almost three times greater than the one of coal of oil that have efficiency of 30%, and also significantly higher than efficiency of solar and wind energy.
The main disadvantage of tidal power is that tidal power plants are very expensive to construct meaning that tidal power is still not cost-effective when compared to fossil fuels, though it has to be also said that once tidal power plant is constructed maintenance costs are relatively low.
Also in real life harnessing tidal energy can be only done on a coast with a good tidal differential which means that not many sites are actually suitable for this kind of power generation, and it also only produces electricity during tidal surges which is in average around 10 hours each day.
Tidal power can also have negative environmental impact; the frames of the turbines can disrupt the movement of large marine animals and ships through the channels on which the barrage is built, while construction of tidal power plant can disrupt fish migration in the oceans, and even kill fish population when passing through the turbines.
While there is no doubt whatsoever that tidal power has great potential there are also some serious disadvantages that prevent tidal power from becoming commercially viable. The tidal power technology still needs lot of development in order to become cost-effective, because great potential alone is not enough to make tidal power competitive with currently dominant fossil fuels.