Ocean colonization is the theory and practice of creating large permanent human communities at sea, potentially hosting hundreds of thousands of residents each. Such settlements may float on the surface of the water, or be secured to the ocean floor, or exist in an intermediate position.
One purpose of such colonization is to exploit en masse the renewable energy potential of the sea in order to meet the tremendous energy demand of civilization. As the planet's largest solar energy collector, the sea represents our greatest reserve of renewable energy. Another is the mining of resources found in the oceans, including methane hydrate.
OTEC or Ocean thermal energy conversion is both a means and a reason for the existence of ocean colonies. OTEC is an old, simple, well understood, and well-proven renewable energy technology that has remained largely under developed today owing to the remote nature of the marine locations and large minimum system scales it requires. OTEC functions like any solar-dynamic power system –such as large solar-dynamic plants based on vast solar mirror collector arrays and a thermal fluid. The difference with OTEC is that the solar collector is the ocean itself, the system running on the difference in temperature between warm surface seawater and cold deep seawater. Thus the effective solar collection area of an OTEC plant covers many thousands of square kilometers, making OTEC plants the largest solar energy systems possible on Earth and the most economical. The use of OTEC systems for renewable energy has the benefit of producing both copious amounts of fresh water and upwellings of nutrient rich deep sea water akin to the natural marine upwellings that commonly fuel the major fisheries of the world. Tapping this source of water to support mariculture facilities -which in turn would support intensive hydroponic farming facilities- has the potential to become the world's primary source of food aid for struggling nations or disaster-struck communities. Unlike conventional farming, there is no fossil fuel used in the production of food by this technology and a greatly reduced labor overhead, resulting in a radically reduced cost.
The critical logistical factor in the development of marine settlement is transportation and the chief obstacle to date to the successful colonization of the sea has not been any lack of technology for building and living at sea but rather the severe gaps in cost/performance of contemporary transportation systems when it comes to serving locations in the mid-ocean.