Electricity
Generation, transmission and the caps you will eventually hit.
Generating power
Introduced in Bleak Beach, where you have to light a town stuck in permanent darkness. One generator can be crafted and placed anywhere; the rest — windmills, waterwheels, furnaces — need kits and helper Pokémon. Most run forever; the Furnace has to be fed burnable items periodically.
Almost every powered item draws exactly 1 unit; a few — string lights, surface lights — need power but draw 0. Overload a circuit and it shorts: everything on it dies until you add another generator.
Transmission
Utility Poles come first — effective, but they eat vertical and visual space. After Porygon's request in Sparkling Skylands you can craft Wireless power transmitters: 1×1×1 blocks that carry power a long way and, unlike poles, through objects. A craftable Switch cuts transmission to anything wired directly to it.
Each pole or transmitter feeds up to 20 things and connects to one generator directly, though power from several generators can travel along a shared line. Distance is Manhattan, not diagonal, and power will not climb or drop more than 5 blocks vertically in a single hop.
Hard caps
Per area: at most 64 generators in any combination of Mini Generators, Windmills, Waterwheels and Furnaces — which works out to between 320 and 1,920 units depending on the mix — and no more than 1,024 powered items at once. Place more than 256 transmitters and any further ones simply stop working.
A Charging Station shows how much power is stored — up to 40 units, one indicator light per 8 units. Dens and huts are not wired by default, but a Mini Generator placed inside powers everything in them; cottages and houses power their whole interior once connected.