One thing that a strong build out of onshore wind does is increase the returns to offshore wind, because of the portfolio ~ when you have harvesting of one volatile power resource already in the portfolio, adding an additional power source that is not strongly correlated reduces the volatility of the total of the two.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.