Whilst the game has very high production values and an interesting mechanic, the limit number of shots for the towers doesn't work as a mechanic so well. Please do be disheartened, it's been quite a while since I've seen someone try something new with the genre, and you definitely have the skill to make a great game with original features. Perhaps having the towers periodically re-load instead of disappearing? A greater variety of towers? placible one-shit traps? This has the potential to be a great game, please keep at it!
Suggestions for future versions:
A tech tree for advanced upgrades, buildings etc. such as carbon capture or thorium nuclear power.
Hydroelectricity (Dams, tidal turbine, barrages).
Trees, carbon scrubbing etc. Air synthesis petrol.
Separate oil and gas wells could make more versatile scenarios.
Biofuel power plants, different farm types (traditional, factory, organic).
Bigger maps, population centres, rivers and seas.
Awesome game 5/5. Would love to see a third one someday.