Yeah, I mostly agree with your gist, although I feel you have straw-manned me with the points you brought up;)
> NZ doesn't actually have a lot of land suitable for solar that doesn't have higher-value uses
Do you have any references? I know somebody involved with a bid, and solar could heavily outbid farming ($ per hectare per annum) for the location they looked at. A solution only needs some land, not “a lot of land” as you put it, although there are constraints and objective function variables (hours of sunshine, nimby, high voltage network access, land value per hectare, , etcetera).
> rooftop solar
Expensive wasteful rooftop solar makes economic sense for some individuals, which really shows up the inefficiency of our electricity market design, since utility scale solar generation makes more economic sense in New Zealand. Government intervention would be useful if it fixes market failures.
> hydro operators don't need subsidies
Psychologically loaded point. An electricity market should be designed to price in long-term requirements (like security of supply, CO2 costs, network reliability), which could be thought of as cross-subsidisations. Of course, be very careful of perverse market incentives (law of unintended consequences). . . https://www.sas.upenn.edu/~haroldfs/540/handouts/french/unin... The government could invest in high-risk research, even if network generators/operators are freeloading, so long as it helps NZ much more than it costs, we all win.
Sometimes the government can take on risk, for example the broadband fibre rollout. I strongly disagreed with that at the time: the goal of technology literacy was a lie and the system looked to me like a subsidy to NetFlix et al. Although it happened to work out well during Covid lockdowns, and it looks like it will make financial sense to the government, and hopefully the social gains well outweigh the social losses.
Private markets can’t make long term investments if the cost of utility scale infrastructure is dropping too fast. This is a market failure that can be fixed by appropriate financial incentives (regulation or market design to pay for the long term gains to the country).