Connect 2 powers together (and place the hub), you can then continue to sell power after you connect any additional stations. So if you connect a resource station to the hub before you connect a station that uses that as a required resource, it will stay on the list of sellable items. I thought that was cool until...
Problem is there is no way to set the Buying AND Selling price. So now either my hub sells energy for 19..and buys it (for 19)
or sells for 13 and buys it for 13 . I also like to have pirates buy my space weed, so I can't turn off sell to others. Guess I'll have to go back to a save game and plan the order.
FYI for those that place HUGE hubs at once.