Pretty cool, I think one thing to add would be a way to visualize the amount of energy going to a shield so you can see how having all valves open is less effective.
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I see what you mean with having the player discover the mechanics, but isn't not showing information detrimental to the gameplay? It creates a brief mystery at first but for the most part the player is just left uncertain and can never really grow because it's harder to judge if what they're doing is wrong.
Hmmm, I'm unsure. I don't think hidden information is always detrimental to gameplay. I also think that if you're paying attention to the shield visuals it is obvious that opening a single valve to one shield charges it so much quicker than if you've got all the valves open charging all the shields. Maybe the potential player uncertainity you mentioned would be mitigated by adding the UI elements I mentioned in my other response which should make the charge level of a shield and its rate of change more readable.