When I first upgrade my shielding to 3 bars, I tried powering it up. However it says "Requires System Upgrade". What system upgrade do I need to power this up? I have enough reactor energy so I'm not sure what I need. Do I have to buy it from a merchant?
You need 2 shield upgrades for another point in shields, so if you have an uneven number of shield upgrades you need to add one more to actually make use of it.
2 points in shields => 1 shield
4 points in shields => 2 shields