Medium & Large Reactors
The Medium Reactor is a larger 3x3 variant of the existing 2x2 "Small" Reactor. It costs twice as much but produces three times as much power, making it overall more cost-effective than an equivalent number of Small Reactors.
The Large Reactor is an even larger 4x4 version. It costs four times as much as the Small Reactor but produces nine times as much power, making it by far the more cost-effective option for large ships.
In addition to producing power more rapidly, these new reactors also make bigger batteries. The Medium Reactor produces batteries that are twice the size compared to the Small Reactor, and the Large Reactor makes batteries three times the size of the Small Reactor. This allows crew to carry much more power per trip, further cutting down on the overall cost of using Medium and Large reactors compared to using multiple Small Reactors.
These new reactors have their own downsides, though. Most importantly, the Medium and Large Reactors have much larger explosions when they are destroyed, so you'll need to be very careful about protecting them. Here's an example of a Large Reactor exploding:
Additionally, when crew pick up batteries from a Medium or Large reactor, it takes a small amount of time to fill the batteries. A Medium Reactor battery takes 0.5 seconds to fill, and a Large Reactor battery takes a full second to fill. (Small Reactor batteries still fill instantly.) This makes Medium and Large reactors less useful for directly supplying power-hungry systems like Shields and Ion Beams than the Small Reactor.
The most effective way to utilize Medium and Large reactors is to have them in central locations relatively far from the weapons and other systems that need their power, but to have closer Power Storage rooms to quickly supply power. Your crew will pick up power from the Medium or Large Reactor and carry it to the Power Storage (ideally utilizing Moving Walkways for maximum speed) where, upon delivery, the double- or triple-size battery will "split" into multiple single-size batteries, ready for quick delivery to the nearby systems. You can use the crew A.I. customization tools added in the previous updates to setup smart "supply chains" between reactors and storages.