Engineers

Engineers for your ship are recruited by spending Rank Points. Each Rank Point spent recruits 2 Engineers. Each Engineer increases your maximum Energy capacity by 1 point. So spending a levels worth of 5 rank points hires 10 Engineers (5 Rank points x 2 = 10), increasing your max energy by 10.

There are several Missions that will reward you with additional Engineers as well.

Engineers increase total Energy capacity. They have no effect on energy recharge rates. To increase your energy recharge rate, build Relays.

Engineers are included in your ship's total crew that helps you in Raiding enemy ships, and defending against enemy raids.

Engineers take up no ship space whatsoever and have no upkeep cost. How and why they work so frugally is a matter of much debate. But it gives a good reason for considering using rank points for Engineers instead of for increasing Deck Spaces for expensive energy modules.