A sea breeze or onshore breeze is a gentle wind that develops over bodies of water near land due to differences in air pressure created by their different heat capacity. It is a common occurrence along coasts during the morning as solar radiation heats the land more quickly than the water. A land breeze or offshore breeze is the reverse effect, caused by land cooling more quickly than water in the evening. The sea breeze dissipates and the wind flows from the land towards the sea. Both are important factors in coastal regions' prevailing winds.
Offshore wind refers more generally to any wind over open water. Offshore wind farms take advantage of the higher wind speeds available over the sea, but are usually placed near coasts to reduce costs and to take advantage of daily flows of sea and land breezes. Nearshore wind farms are those closest to land, while others are further out to sea.
The sea has a greater heat capacity than land, so the surface of the sea warms up more slowly than the land's surface. As the temperature of the surface of the land rises, the land heats the air above it by conduction. The warm air is less dense and so it expands, decreasing the pressure over the land near the coast. The air above the sea has a relatively higher pressure, causing air near the coast to flow towards the lower pressure over land. The strength of the sea breeze is directly proportional to the temperature difference between the land and the sea. If a strong offshore wind is present, that is, a wind greater than 8 knots (15 km/h) and opposing the direction of a possible sea breeze, the sea breeze is not likely to develop.