The feats of engineering in offshore wind are becoming truly astonishing, for a simple reason: the amount of energy you can extract from a turbine depends mostly on its swept area. But also, crucially, the greater the bonus becomes for adding more length.
If your turbine has a 20m (85.6ft) diameter, and you add one further meter (3.3ft) to that diameter, you gain somewhere around 34 square meters (366 sq.ft) of additional swept area. But if your turbine starts with a 50m (164ft) diameter, adding one extra meter of diameter brings in about 79 extra square meters (850 sq.ft) of swept area, since that extra blade length is sweeping a bigger circle.
Thus, the ever-growing size of these things is getting almost ridiculous. A turbine currently under construction in China uses 128m (420ft) long blades for a whopping 260m (853ft) diameter and a 53,000 sq.m (570,490sq.ft) swept area. That's equivalent to 9.9 NFL football fields or 42.4 Olympic swimming pools.
Think that's enormous? Well, wait for the new turbine proposed for 2025 by China's MingYang. According to Bloomberg, it will have a rotor diameter over 310m (1,017 ft), corresponding to a swept area of 14.1 NFL football fields or 60 Olympic pools.
Add on a little clearance to make sure the blade tips stay out of the water, and you'll probably be looking at something taller than New York's Chrysler Tower, or the Eiffel Tower in Paris - but spinning.
What's more, these huge offshore turbines are extremely expensive to install, and the economics of deployment and grid connection tend to work in favour of fewer, larger turbines than more, smaller ones.