• Windy spots onshore are running out - in the case of a small state like Portugal what I can tell you is that we are now moving into wildlife protection areas (usually mountain just tops). The only spots left are national wildlife parks - spaces were human intervention is reduced to the least as possible by law. This is the main reason why our government is trying to support the development of a Wave power industry. In the case of the US there are entire states where Wind is not an option by lack of proper high terrain.
• Wind is a better resource offshore - windmills deployed offshore tend to work more time than onshore. Load factors (the percentage of time a turbine operates during a period, say an year) are usually 10% higher onshore than offshore - increasing from 25%-30% to 35%-40%. This extra wind provides for the extra logistics of deploying these incredible structures at sea. There's another important characteristic of Wind offshore: it tends to be more stable and to some extent easier to predict -this will have an important role in load balancing the electric grid.
• The visual/environmental impact is lower at sea - onshore wind turbines have a true impact on the landscape, being this one of the major obstacle to its public acceptance. They also have a negative on bird life - especially in mountainous territory, where some studies showed them to take a real toll on preying birds. As far as I'm aware, offshore, the main potential impact on wildlife is on migratory birds. But a Danish study a few years ago showed that these birds can actually avoid the farms altogether, and even if crossing them these birds seem to be able to individually avoid the turbines and its blades, unlike their preying kin. Offshore wind farms can be designed in ways to actually have a positive impact on marine wildlife, although this is an issue I still have to study properly.

Right now my own reserves are on turbine lifetime, something for which data effectively doesn't exist yet. But given the heavy industry experience with oil and gas production and transport I expect whatever obstacles to appear on that chapter to be overcome with time.


Vencit omnia veritas.

1. some countries are running out of space onshore

2. offshore, you can build wind farms like actual powerplants, on a GW-scale (with hoped for economies of scale and industrialisation, ie more potential to bring prices down and th possibility to replace large chunks of the power generation system

3. wind is a better quality (less turbulence) and can be harvested at a higher altitude (where it is stronger)

4. logistical issues prevent from building bigger turbines onshore as they cannot be transported around. Putting factories by the seaside for offshore use solves that.