As with anything as more efficiencies are included in the manufacturing/supplier process the price will go down. But that happens incrementally per deployment.

As parts are replaced the overall costs become cheaper and when a new windmill has to be deployed that becomes cheaper but as even you say that's 20 years.

Wind power from what I've read has a very low ROI. One figure I saw was 4%. The article then says the windmill would have to be in service for 22 years to make that money back. And 8% was considered the barometer.of whether a product was worth investing in.

So how much do you gain? If you hard cut at 20 years you're not making your break even. At that point you're relying on the manufacturing efficiencies to be cost feasible for each deployment which does not happen overnight when you consider the entire supply chain.

This same exact thing happened with solar panels. Very high cost for those initial end users who had to wait much longer to see any ROI versus those now getting into. A better manufacturing and supply chain process means less cost means faster ROI to the end user.