System

Tidal barrages are the main source of converting the tidal power into usable energy in the form of electricity. This method uses a large dam structure, known as a barrage, that forces the tide to flow in and out of tunnels within the dam structure.  The force that is in water flow then turns a turbine or forces air pressure through a pipe that in turn, moves the turbine. This process allows for energy to be harnessed consistently with the daily movement of the tides. 

The left graph is the real and theoretical power equations graphed relative to the head height this shows how the power output increases as head height increases. This makes sense, the interesting thing is how the difference of total power output is smaller with higher head. This difference is the efficiency of the done or percent difference between actual power and theoretical power. The lower right graph shows how the efficiency does increase with head height but is far more than it looks from the first graph so it shows that the dam needs as large of head as it can get. 

The calculations show that the turbines are turning 37% of the potential power into electricity at a head of 1.95m and increases up to 87%. This is calculated by finding the mass flow of the water using interpolation from data points taken from the tidal power plant. The volumetric flow rate is then multiplied by the density of salt water. Then, this function is plugged into a modified Bernoulli's equation that does not account for any losses. The equation multiplies the mass flow rate by the acceleration of gravity and then by the head height. This gives the theoretical maximum power in the flowing water. This is then compared to the actual power output of the dam to find the efficiency. The actual power equation is an interpolation from data points taken from the tidal power plant, this is why it is a cubic function without units. We can see from the efficiency graph that the efficiency is starting to approach its max, so increasing the head will not raise the efficiency significantly. 

There are several other ways to increase the efficiency of this system. The efficiency is connected to head height so keeping the head as high as possible is the most ideal, but this is not very possible as tides are uncontrollable. Raising the level of the lake is also not a possibility, doing so would flood homes. This leaves us with the option of improving the turbines. Increasing seemingly insignificant variables, like the smoothness of the walls, would help but this is a very well refined option as there are so many dams. So, the Sihwa power plant is likely as good as it needs to be. This system differs from other dams though, as the head height is more often low, so it would be good to have a second set of turbines that are the most efficient from 2 to 4 meters of head height. Then, when the water height is at that range, divert the flow through the new turbines to increase the overall efficiency. However, this last option is expensive and would require a ton of work and might just not be worth the expense.