People have utilized tides for energy since the Egyptians in 200 AD. They had simple systems that used the tides to irrigate fields by pumping water down a network of canals spanning large fields.
Then came the use of water wheels to grind grain. The first itteration of these wheels relied on the flow of water passing by. This was a slow process that only assisted in the grinding process, but could not take it over fully. Later on, these systems expanded to capture the high tide behind a gated damn and release it during low tide. These systems not only powered the milling completely, but could run the entire interval between a low tide and high tide: 6 to 8 hours.
Today, we are looking towards the tides to help with the energy crisis. Scientists are still looking for the best way to provide power but they have come up with a number of promising solutions. They have use large damns, similar to the systems used to grind wheat, with multiple turbines, but found them to have a terrible ecological impact. A system finding popularity today place windmills or turbines, shaped like a lawn mower blade, under the ocean to directly gather energy from the incoming tide. This solution is able to generate hundreds of megawatts under the right condition, providing a sustainable alternative to fossil fuels.
The tides offer a predictable energy source that would compliment the unpredictability of solar and wind energy. By combining all the renewable options, we could rid ourselves of our dependence of fossil fuels.