Billions of dollars have been expended on oceanic energy. So far, the only OTEC operating is in Hawaii and it isn't doing what it was supposed to do. Offshore Wind Farms exist, cost billions and the power costs millions in cabling per mile, to transmit
Costs millions to purchase ready-to-use equipment, more for stocking, more for feeding, requires permits, and has proven to both pollute and spread disease within 'wild' forms of sea-life, as well.
Depends on what you are talking about, but it has to be built, which requires a facility, supplies, energy, laborers, sanitation and Lord only knows what permits and pollution controls the local government will require, not to mention meeting the standards where built, and where utilized.
Limited choices 1-if-by-air, 2-if-by-sea... Neither is very cheap, or cost effective, which is why ships and boats are built in land-based facilities, not at sea.