Other great resources: Official JS API docs, Scripting Forum
POWER_GEN
a power generator, required to "power" oil derricks
what actually happens is that power gens burn oil generated by derricks to produce $ (but everyone refers to $ as "power") - somewhat confusing game mechanic really - more on that here: http://forums.wz2100.net/viewtopic.php?f=3&t=8828&p=93202&hilit=+power#p93199
usually there is a limit of 5 power gens per player. game settings allow limit to be set between 0 (none) and 5. some mods exist that allow more.
one power gen can "power" 4 derricks