Offshore wind farms, built in the sea rather than on land, have expanded rapidly in several countries. Winds at sea are generally stronger and more consistent than on land, so offshore turbines can produce more electricity. They are also less visible from homes, which can reduce local opposition. Building at sea, however, is more complicated and expensive. Turbines must withstand storms and salt water, and cables must be laid along the seabed to carry electricity to shore. Most existing offshore turbines stand on foundations fixed to the seabed, which limits them to relatively shallow water. In deeper water, engineers are developing floating turbines anchored to the sea floor by cables. Environmental effects are still being studied. Construction noise can disturb marine mammals, but some researchers have observed that the foundations of turbines provide surfaces on which marine organisms grow, attracting fish. Fishing communities have expressed concerns about losing access to fishing grounds. Planners increasingly try to involve these communities early in the process in order to reduce conflict.

Winds at sea are generally stronger and more consistent than winds on land.