New transmission tower allows you to import electricity for factories. Must be built at the edge of the map.
Now factories need energy, either coming from imports of neighboring cities, or a nuclear plant. Factories are the only building that requires energy, in the same way agriculture needs water.
Likewise, nuclear power plant provides electricity for factories and allows the city to build a lot more than the limit of 4 towers when using only imported energy.
Old cities that had factories without power will continue to work just fine, but new factories will require power.
