Curious to know if something bigger was in the plans, or perhaps the road also have/had other uses?
Additionally, the reservoirs formed are important for making the system provide reliable power to match demand - demand for power in Quebec peaks in the coldest parts of winter, and the natural peak of runoff/river flow....is not then.
So, the generation out there is useful but is not the primary reason why the road was built all the way out to there.
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No special insight on the difficulty/expense of constructing the transmission, but ~788MW of extremely cheap power forever for constructing/maintaining ~130mi of extra transmission doesn't seem completely improbable to work out financially, especially at the time.
I'll also note:
- Vegetation maintenance costs are probably low given how slow things grow out there.
- This was constructed long before the modern era of cheap(er) renewables.
- Even today, Quebec's location, weather, and time of year of peak demand make the calculation for solar's cost-effectiveness a lot harder.