Add multi-unit combined cycle gas turbine component by jfrederik-nrel · Pull Request #232 · NatLabRockies/hercules

jfrederik-nrel · 2026-03-07T01:52:26Z

Work in progress. Still to do:

Merge latest version of feature/mm-thermal back in
Execute sanity check of the control logic
Clean up code, ruff
Complete the example, possibly merge with existing example
Write documentation
Add tests

No reviews necessary yet at this time.

…m-thermal

This reverts commit 71f3c90, reversing changes made to bb51e82.

…mal right now

dzalkind · 2026-03-19T19:38:26Z

+                "For the combined cycle plant, one of the units must be an open cycle gas turbine."
+            )
+
+        if len(generic_units) != 2:


We may want to relax this constraint in some cases in the future, where multiple gas generators could be combined to feed a steam unit. We can probably work around this for now.

Will the code break in this case? I'm not sure we should change it now, but it might be good to know in the future.

Yes, I was thinking about that too. What I think I will try to do on the short term (though perhaps not in this PR) is allow at least 2 (or perhaps more? From what I can find, 2 is currently the max) gas units powering a single steam unit. I don't think that would break anything, but definitely not excluding the possibility that it causes complications that I'm currently not overseeing.

dzalkind · 2026-03-19T19:41:57Z

+
+        # Update h_dict with outputs
+        h_dict[self.component_name]["power"] = self.power_output
+        # h_dict[self.component_name]["state"] = self.state.value


Do you want the state or is it not needed because each unit has its own state?

Each unit has it's own state. We would need to define a new state machine for the combined unit as it has complicated combined states like "gas turbine on, steam turbine off". I refrained from doing that and just left it at each unit having its own state

dzalkind · 2026-03-19T19:44:09Z

+        return h_dict
+
+    def control(self, power_setpoint):
+        """"""


Maybe denote that this is the control of the combined plant?

dzalkind · 2026-03-19T19:44:46Z

+            1 - self.gas_power_ratio
+        ) * power_setpoint
+
+        # TODO: we probably want to add an actual controller for the gas turbine


It looks like you did this TODO?

No I didn't. I meant that right now it uses the basic _control logic defined in the thermal_component_base class, as there is no control method defined in the open_cycle_gas_turbine class. What I meant here is that we might want to add that at some point, or else rename _control in thermal_component_base to control.

dzalkind

Overall, this looks good to me. Nice job!

I like the power set point input addition. It might be nice to have that documented for future reference, along with making sure your new docs are included.

Otherwise, I left some small comments in the files; they are pretty minor and often for my understanding.

jfrederik-nrel · 2026-03-19T20:12:49Z

@dzalkind it should follow #224. #225 is related, but a stand-alone PR I'd say.

I merged #224 into this branch recently, so I don't expect any major merge conflicts.

Added the missing combined_cycle_plant doc.

genevievestarke · 2026-05-12T16:53:19Z

Ok, I've merged in develop but I have a few questions:

We now have a hard_coal_steam_turbine model and a steam_turbine model. Are these two meaningfully different?
There's some code on lines 632-638 in thermal_component_base.py that I've commented out that I'm not sure if we need anymore. @jfrederik-nrel, could you take a look at that

jfrederik-nrel · 2026-05-12T17:14:29Z

@genevievestarke

They can probably be merged at some point, I agree. I created the class steam_turbine since I think the other class didn't exist yet when I started, and then it didn't seem applicable for the purpose of the multi-unit CCGT since it doesn't use hard coal as fuel. So I think we can probably remove the current steam_turbine model and rename the hard_coal_steam_turbine model to steam_turbine, while keeping everything in it the same. Do you want me to do that and check to see if that breaks anything?
I think you're right that it can be removed because the exception is now captured in calculate_fuel_volume_rate.

genevievestarke · 2026-05-12T18:31:31Z

For #1, that would be great!

Also, there are two example 07s now, so I'll take a look at that, as well.

genevievestarke · 2026-06-02T21:00:27Z

+
+Similar to the `ThermalPlant` class, the `CombinedCyclePlant` class does not have many default parameters. Key attributes that must be provided in the YAML configuration file are the `OpenCycleGasTurbine` and `SteamTurbine` `units`, which is a list that is used to instantiate the individual thermal units that make up the plant, and `unit_names`, which is a list of unique names for each unit. The number of entries in `units` and `unit_names` must match.
+
+However, unlike the base `ThermalPlant` class, it is recommended that some parameters are defined outside the individual thermal units. Since the gas turbine does not have its own individual fuel source, instead using the rest heat from gas turbine, it is not possible to specify the efficiency and fuel consumption of the steam turbine in the same way as done for individual components that are not linked. As a result, these outputs are instead calculated for the plant as a whole, necessitating an efficiency table for the unit as a whole. Note that this table is only used when both the gas and steam turbine are running. If only the gas turbine is running, the `OpenCycleGasTurbine` efficiency table is used instead.


@jfrederik-nrel in the second sentence, should it be steam turbine first?

The yaml file should contain a unit of OCGT and a unit of ST. The order doesn't matter, if I understand your question correctly.

Ah, I'm specifically asking about the wording of the documentation: "Since the gas turbine does not have its own individual fuel source, instead using the rest heat from gas turbine, ..."
This sounds like one of the gas turbine references should be referring to the steam turbine?

genevievestarke

Really good work @jfrederik-nrel ! I just had a question about whether you can simulate multiple combined cycle units in the same plant or not? To create a whole plant, do you just scale the OCGT rating and the ST rating to account for all the units in the plant?

genevievestarke · 2026-06-02T21:36:58Z

+
+###
+# Describe this simulation setup
+description: Combined Cycle Gas Turbine (CCGT) Example


Is the current implementation simulating just one OCGT+ST? Can you simulate multiples of these pairs? It seems like only one can be defined per CombinedCyclePlant. If you can assign multiples of these in the multi-unit plant, then maybe CombinedCycleUnit would be a better name?

Currently, you can only have one OCGT+ST, so yes, you would need to scale them to model a more complicated setup that for example has two steam turbines (which I do think is actually relatively common). I did consider making it generalizable, but this would severely complicate the control logic as there are many ways the different units could be linked. I therefore chose to keep it simple for now and stick to a single OCGT+ST setup. The nomenclature doesn't seem overly important to me personally, but if you want to change the name to CombinedCycleUnit, I won't fight you on it.

Ok, since it's meant to represent the whole plant, I'll keep it as is for now!

dzalkind and others added 29 commits March 4, 2026 14:37

Update constants, instructions for nrel-pysam 7

b6bd44c

Update toml

e34ebef

Merge remote-tracking branch 'upstream/develop' into pysam_7

a16621d

First pass run through for multiunit thermal plant

bb51e82

Merge branch 'pysam_7' into feature/mm-thermal

71f3c90

Add logging for individual units within thermal plant

0176b6f

Merge remote-tracking branch 'misi/feature/mm-thermal' into feature/m…

f50a34a

…m-thermal

More formatting

5a71cc2

Merge remote-tracking branch 'misi/feature/mm-thermal' into feature/m…

0feae7b

…m-thermal

Add steam turbine module

84cf038

Improvement on loading units into thermal plant

c9b8940

Bug fix for when there are multiple of the same units in a plant

6f9991d

Track number of starts

65c3955

Merge remote-tracking branch 'misi/feature/mm-thermal' into feature/m…

b37678c

…m-thermal

Make array of units flexible, hacky

b458dbc

Make array of units flexible, hacky

0f6f949

Revert "Merge branch 'pysam_7' into feature/mm-thermal"

9f1d377

This reverts commit 71f3c90, reversing changes made to bb51e82.

Track starts in h_dict for outputs

7fe5752

Merge develop

8156bb0

Formatting

ee48564

Clean up dostrings

056695d

Add note that initial conditions are correctly set on h_dict

aaefd88

Docs page for thermal plant

390cfa9

Check that units are all thermal

d3ea4c1

Add tests for ThermalPlant

493e661

WIP

137284b

Merged mm-thermal in

8f24c7d

Fixing merge conflicts

203c91e

Multi-unit CCGT now functional, probably in the same state as mm-ther…

1c55931

…mal right now

misi9170 mentioned this pull request Mar 9, 2026

Multiunit thermal plants #224

Merged

dzalkind reviewed Mar 19, 2026

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Comment thread docs/_toc.yml

dzalkind reviewed Mar 19, 2026

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Comment thread examples/07_open_cycle_gas_turbine/hercules_runscript.py Outdated

dzalkind reviewed Mar 19, 2026

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Comment thread examples/07_thermal_plants/hercules_runscript.py

dzalkind reviewed Mar 19, 2026

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dzalkind approved these changes Mar 19, 2026

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Added missing docs

9cee66d

paulf81 mentioned this pull request Apr 7, 2026

New thermal plant class that models down to the turbine level #213

Closed

genevievestarke mentioned this pull request Apr 8, 2026

Move the component registry out of the hybrid_plant file #237

Closed

Merging in develop to this branch

f92e1ee

Frederik and others added 10 commits May 13, 2026 13:59

Deleted old example 7

d0c7642

Merge classes HardCoalSteamTurbine and SteamTurbine

40fc259

Debugging, removing final HardCoalSteamTurbine class references

99f2ce0

Fix example 07 tests

27cebb6

Fixed tests

f90fcba

More test fixes

3eb1917

Format combined cycle plant test

64bb8f1

Fix steam turbine test formatting

c407bb8

Fix formatting

e579899

Fix formatting

adb6df9

genevievestarke reviewed Jun 2, 2026

View reviewed changes

Genevieve Starke added 2 commits June 2, 2026 17:28

Update docs

2af15a8

Update docs toc

623276e

genevievestarke reviewed Jun 2, 2026

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		Similar to the `ThermalPlant` class, the `CombinedCyclePlant` class does not have many default parameters. Key attributes that must be provided in the YAML configuration file are the `OpenCycleGasTurbine` and `SteamTurbine` `units`, which is a list that is used to instantiate the individual thermal units that make up the plant, and `unit_names`, which is a list of unique names for each unit. The number of entries in `units` and `unit_names` must match.

		However, unlike the base `ThermalPlant` class, it is recommended that some parameters are defined outside the individual thermal units. Since the gas turbine does not have its own individual fuel source, instead using the rest heat from gas turbine, it is not possible to specify the efficiency and fuel consumption of the steam turbine in the same way as done for individual components that are not linked. As a result, these outputs are instead calculated for the plant as a whole, necessitating an efficiency table for the unit as a whole. Note that this table is only used when both the gas and steam turbine are running. If only the gas turbine is running, the `OpenCycleGasTurbine` efficiency table is used instead.

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jfrederik-nrel commented Mar 7, 2026 •

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