[erentz]

Hydro plants are already going to be running at full output during the peak demand time when solar is not working. Just because you have solar during that day, which means you get to use less of the stored hydro water during the day, does nothing to increase the generating capacity of the hydro plant at peak time. The turbines and generators are already certain size and turn a certain speed. They don’t get bigger because you used less water at midday.

So to make hydro work as a storage solution you need to build more hydro than what you currently have already to replace fossil generation and make sure you can meet all your evening demand. That is absolutely not going to happen anymore, in developed countries hydro is well tapped and nobody wants more dams or lakes. In developing countries there may be some potential but it won’t meet all demand.

There needs to be another storage solution for solar to become viable in this way.

[robocat]

> Hydro plants are going to be running at full output during the peak demand time when solar is not working.

How do you know that?

During drought periods surely it's not true (if there's not enough water to run them).

The flow of rivers is controlled to some extent (which may prevent saving during the day and generating in evening).

And presumably it might be true in one country, but not another, depending on a raft of factors.

I'm guessing there is data somewhere showing utilisation of hydro during evening.

[erentz]

Part of it is based on previous experience working for the national grid in a hydro rich 80-90% clean generating country. I can’t speak specifically for the US but think about it like this. You need to have enough generating capacity on your grid to meet the peak demand. Which according to this duck graph is when solar is not generating. But we have not overbuilt capacity by some large margin. And hydro is only some portion of that total capacity today. The rest is coal, nuclear, increasingly gas, and some small amount of renewables. Therefore how can hydro alone meet the all of the demand when you remove the goal, gas, etc.

[robocat]

Can your reference some live data?

I had a look at https://www.transpower.co.nz/power-system-live-data

And that showed hydro was running at less than 50% of capacity for one relevant data point.

I am guessing the data series of hydro usage versus capacity is available for NZ. Finding out the constraints and understanding them is more difficult.

Your point of maximum capacity may be true, but we are talking usual daily usage (duck graph) and whether solar can use hydro for that.

In think you are arguing about occasional peak network capacity (e.g. heat wave) which is an outlier and you retain power stations with extremely low utilisations for those abnormal peaks (and ignore green issues).