A bit of a correction. The cost of wind farms has come down...

A bit of a correction. The cost of wind farms has come down since 2009.
"Typical cost is $1.3 million per megawatt (MW) of electricity-producing capacity"
https://weatherguardwind.com/how-much-does-wind-turbine-cost-worth-it/

So 100MW of wind capacity would have a capital cost of around US$130mill.
Solar looks a bit more expensive at A$190m or around US$142M.
"Sustainable Energy Research Analytics recently estimated the capital cost of the $190 million 100MW Clare solar farm"
https://reneweconomy.com.au/agls-new-200mw-silverton-wind-farm-to-cost-just-65mwh-94146/

However wind or solar or even a combination of the two are not nearly as reliable as hydro. Solar is only good for up to 12 hours a day and wind can be low for days at a time. To get a consistent average of 100MW day and night as you can get from hydro might need at least 150MW of installed capacity of wind and/or solar with a large battery also likely to be required. So I still think capital cost for solar/wind green hydro will cost close to three times as much as an equivalent 100MW hydro project.

Then there is maintenance for wind that MNB won't have;

"Wind Turbine Maintenance Costs

Once built, maintenance is an ongoing expense.

• 1-2 cents per kilowatt-hour produced"

https://weatherguardwind.com/how-much-does-wind-turbine-cost-worth-it/

Just that wind turbine maintenance cost is equivalent to MNB's total cost of electricity. Crazy stuff.

One more note, the $120mill for 100MW electrolyser is only to generate the hydrogen. More will be required for the ammonia plant.