I posted my seastead concept over at SSI. Here's a link to the post along with the concept overview. If you want to see the pretty pictures and a more thorough explanation of the concept, click the link and check it out.
GenSeneca's Seastead Concept
Conceptual Overview: A floating platform is used to harvest seaweed and/or kelp, which is then turned into mash and distilled to make ethanol. The ethanol is burned in turbines which power the platform, farming vessels, and a small bulk carrier. The used mash is dried into powdered seaweed/kelp, loaded onto the small bulk carrier, and sold in bulk at a nearby port.
Harvesting one acre per day will produce just over 2400 gallons of ethanol, half of which is used to create a minimum of 30 MW and a maximum of 70 MW of power for the platform. One of the daily byproducts is roughly 40,000 lbs of seaweed/kelp powder and, if sold for $1/lb, translates into $40k/day income, or $14.6 million per year. There is one last byproduct, the seawater drained from the seaweed/kelp is filtered to make fresh water and stored.