[ASK] What is "overdrive payback"?

Hi all,

This is new for me, and because when I search for it, I found only changelog that mention payback, nothing that explain it in-depth.

1) What is the simple calculation explanation?
For example, say I have 1 mex with 100m/s. I have solar (called Solar-1) that can overdrive to +1m/s.
If I build another solar (called Solar-2) that can also overdrive to +1m/s, with solar price is 70m, is the payback time is 70s (only calculate existing Solar-1)? Or it's 35s (calculate Solar-1 and Solar-2)?

2) How can the knowledge of payback helps me to gain advantage? Will I gain more economic advantage if I choose low payback time? What is the priority in having good-payback in general overdrive system? Because I usually just build more mex, connect mex with wind/solar, deplete my met and have abundance energy, I'm confused about having good-payback priority. (Never thinking if this or that generator is more efficient for overdrive or not. I just want to have more energy.)

Thank you for reading and teaching me.

just another feature that isn't explained for new players

It’s a legitimate point; the exact behaviour of ZK eco, especially in team games, is pretty opaque. Most new players don’t even realise income is shared between the team for a few games.