12It Powers Stark Tower
Not the tiny version that lives in Tony Stark’s chest, obviously, but a much larger arc reactor that is situated at the base of the iconic tower. Although this isn’t mentioned in the comics, it’s a major plot point in the Marvel Cinematic Universe. In the films, the larger
arc reactor actually came first, as Howard Stark designed it as a source of clean, renewable energy. Although there were plans to use the reactor technology to supply energy to more of New York, this has yet to happen in the MCU (onscreen, anyway).
During the events of Iron Man, the large reactor was a key part of bringing down the villainous Obadiah Stane. In his final battle with Iron Man, Tony lures Stane to Stark Tower, where he tells Pepper Potts to overload the arc reactor, generating a pulse strong enough to knock out Stane’s armor. Although the original reactor was destroyed in this fight, it has since been rebuilt. Stark Tower became Avengers Tower after the Battle of New York, and Stark continues to laud its power source as the clean energy source of the future.