Version being commented on
Casting Cost: 5

|5

Activation Cost: 5

|5

Effect Unupped:For 5 turns Windmill will generate 2 quanta of your mark per turn.
Effect Upgraded:For 7 turns Wind Turbine will generate 2 quanta of your mark per turn.
This version reminds me of Rustler
Casting Cost:1

|1

Attack:1|1
HP:1|3
Effect:

->

Windmill is a 5

->10mark conversion with an initial cost of 5

and is fixed to one 5 turn conversion every 5 turns
Wind Turbine is a 5

->14mark conversion with an initial cost of 5

and is fixed to one 5 turn conversion every 5 turns
In conclusion, I think that Windmill|Wind Turbine have too high of a casting cost and too high an activation cost (or too slow of an activation).
Suggestions
Mark 1 (probably still UP)
Casting Cost: 3

|3

Activation Cost: 4

|3

Effect:For 5 turns Windmill will generate 2 quanta of your mark per turn.
Mark 2 (probably still UP)
Casting Cost: 3

|3

Activation Cost:

|

Effect:Produce 3 quanta of your mark (can be used multiple times per turn)