Dynamic tidal power is a technology that uses the difference between the potential energy and kinetic energy of tides. Long dams are built from coasts straight out into the sea or ocean—meaning that the tides in the areas where these systems might be implemented usually flow parallel to their respective coasts. During the movement of tides, water on one side of the dam is at a higher level than the other side. As this water flows through the dam it drives a series of turbines installed within the dam and generates electricity. Furthermore, these dams are designed with bi-directional turbines, which flip 180o after each tide in order to generate power both when the tide comes in and goes out. The added output from having bi-directional turbines is a huge advantage for these types of systems since they allow the power output to basically double.
Dynamic tidal power generation remains in the developmental stages meaning that any data is based on models and known tidal behaviour. With that being said, these models tend to be highly advanced and have high confidence in these theoretical predictions.
A dynamic tidal power dam can be 30 to 60 km long and is typically built perpendicular to the coast, running relatively straight out into the ocean. This design does not enclose any area, thus allows more freedom for aquatic life without risk of being trapped. These dams generate a water level difference from one side of the dam to the other—known as 'head'. The head difference (difference in water level between both sides) is predicted to be able to reach up to a few meters. The higher the head difference will result in much higher power production.
In 2015, Canada generated 670 terawatt-hours of electricity. This means that a single dynamic tidal power dam, with an 8 GW installed capacity (this is the theoretical maximum output of a power plant) and a capacity factor of 30% (this is the ratio of actual power output to theoretical power output) could generate almost 4% of Canada's total power output or 21 terawatt-hours annually.
These types of dams, by necessity, tend to be very long (30 to 60 km) which is significantly longer (and more expensive to build) than current coastal structures. However, a long dam can function with multiple purposes such as land reclamation, connections between islands, mainland coastal protection, and deep sea and liquefied natural gas ports. The initial investment costs could easily be shared between these different industries, thus helping to lower the cost per kWh and create higher return investments.
The moon (and subsequent tidal force) isn't going anywhere anytime soon which means that this type of tidal power will be around indefinitely. Furthermore, the tidal cycle is predictable and repetitive which allows us to know exactly when and how much power is obtainable.
Interestingly enough, since these dams are built perpendicular to the shore and the tide flows parallel, dynamic tidal power doesn't require huge tidal ranges. Therefore, these could be implemented in locations throughout the world, which is advantageous over other forms of tidal power (ex. tidal stream generators and tidal barrages) since they tend to require more intense tidal fluctuations in order to be economically viable.
Unfortunately, due to the nature of the tides and the design of these dams, a full project must be built in order to guarantee predicted success. Building a miniature dam would be ineffective since these dams require a predicted minimum length of 30 km to ensure economic viability. Such a dam would require an enormous capital investment and if the design failed a lot of money would be lost. Furthermore, construction of a structure that extends 30 km or further into the ocean has never been attempted—the technology is available but the difficulty is extremely high.
The environmental impact of such a system could be significant. Unfortunately, in areas where any tidal power stations might be built happen to be some of the most densely populated ecosystems in the ocean. Changes in water levels might harm plant and animal life and alter the sea water composition. Also, turbines in dynamic tidal power stations move quickly, and if protection is not built in, marine animals can be caught in the blades. If aquatic life drops in the area, birds typically found there might migrate to different places. An entire major ecosystem could be significantly altered. Further research is needed in order to determine just how large of an impact such stations might have.
It is difficult to determine the cost per MW for these types of power stations since none have been built yet. However, the costs are sure to be much higher than any other field of energy generation.
While the costs are high and the results as yet unknown, this technology may still have a place in the future electrical grid. As technology advances (which it will) and as climate change becomes more prevalent (which is virtually certain) there will be additional pressure to look for power with lower greenhouse gas emissions. Thus, the more that is known about alternative energy resources, the lower their costs. With these lower costs, transitions in power generation will be smoother.