Why ac?

You might wonder why ac is even used. Isn’t it a lot more complicated than dc? Well, ac is easy to generate from turbines, as you’ve just seen. Rotating coil-and magnet devices always produce ac, and in order to get dc from this, rectification and filtering are necessary. These processes can be difficult to achieve with high voltages. Alternating current lends itself well to being transformed to lower or higher voltages, according to the needs of electrical apparatus. It is not so easy to change dc voltages.
Electrochemical cells produce dc directly, but they are impractical for the needs of large populations. To serve millions of consumers, the immense power of falling or flowing water, the ocean tides, wind, burning fossil fuels, safe nuclear fusion, or of geothermal heat are needed. (Nuclear fission will work, but it is under scrutiny nowadays because it produces dangerous radioactive by-products.) All of these energy sources can be used to drive turbines that turn ac generators.
Technology is advancing in the realm of solar-electric energy; someday a significant part of our electricity might come from photovoltaic power plants. These would generate dc.
Thomas Edison is said to have favored dc over ac for electrical power transmission in the early days, as utilities were first being planned. His colleagues argued that ac would work better. It took awhile to convince Mr. Edison to change his mind. He eventually did. But perhaps he knew something that his contemporaries did not foresee.
There is one advantage to direct current in utility applications. This is for the transmission of energy over great distances using wires. Direct currents, at extremely high voltages, are transported more efficiently than alternating currents. The wire has less effective resistance with dc than with ac, and there is less energy lost in the magnetic fields around the wires.
Direct-current high-tension transmission lines are being considered for future use. Right now, the main problem is expense. Sophisticated power-conversion equipment is needed. If the cost can be brought within reason, Edison’s original sentiments will be at least partly vindicated. His was a long view.