PRAS handling of hydro - both run of river and dispatchable

[jhimelic]

How does PRAS handle run-of-river hydro, where there is no reservoir available for shaping capabilities?
I'm I safe to assume it just implements it as a must run and dispatches the unit according to it's nameplate capacity or the fixed dispatch profile we attached to it via a timeseries?

What about hydro that is attached to an upper reservoir (and thus can be shaped to optimize its ability to minimize ENS)? Does PRAS implement a proportional load-following algorithm or something similar?

I didnt see any reference to this resource type in the documentation.

Thanks
Jim

[GordStephen]

Hi Jim - That's right, run-of-river is treated the same as wind or solar, represented as a generator with a time-varying max generation time series.

Reservoir hydro can be modeled as a generator-storage, with a time-varying inflow and the ability to store that "water" (in units of energy) in the reservoir, or run it through the turbines to inject to the grid. Right now all energy-limited resources are only dispatched after generator capacity is exhausted, but obviously reservoir hydro is a pathological case where that doesn't make much sense. We have future plans to implement a merit order dispatch where one could specify that the reservoir should be drawn down before running peaker plants, for example, but that's not implemented today.

The alternative is to manually split the hydro unit into two parts, one that looks like a run-of-river plant (with a predetermined dispatch schedule) and a reservoir unit for the remainder, so that the plant is forced to use some water, but also still retains some flexibility to put some aside for stochastic stress conditions. We've done this in the past to represent min gen constraints, for example.