NatLabRockies · mikkdm · Apr 14, 2026 · Apr 21, 2026 · Apr 28, 2026 · May 12, 2026
diff --git a/docs/technology_models/h2_htse.md b/docs/technology_models/h2_htse.md
@@ -0,0 +1,177 @@
+# High-Temperature Steam Electrolysis (HTSE) Model
+
+The HTSE model in H2Integrate represents hydrogen production from high-temperature steam electrolysis using electricity and thermal input. It is implemented as two components:
+
+- `HTSEPerformanceModel`
+- `HTSECostModel`
+
+The performance model converts electricity and heat into hydrogen, water demand, and operating signals for connected technologies. The cost model computes installed capital cost and fixed operating cost from installed HTSE size.
+
+## Model Overview
+
+This is a simplified HTSE representation with constant nominal specific energy requirements:
+
+- `nominal_electricity_required` in `kWh/kg`
+- `nominal_heat_required` in `kWh/kg`
+
+At each timestep, hydrogen production is determined from:
+
+- installed HTSE size
+- available `electricity_in`
+- available `heat_in`
+- optional `hydrogen_command_value` when system-level control is enabled
+- turndown behavior
+
+The model also exposes internal operating signals that are useful for coupled systems, including:
+
+- `heat_demand`
+- `electricity_demand`
+- `electricity_consumed`
+- `water_demand`
+
+```{note}
+The current implementation uses `electricity_demand` to report installed electrical demand equal to nameplate size, while `electricity_consumed` reports the timestep electricity required by the energy balance. For coupled analyses, `electricity_consumed` is the more literal consumption signal.
+```
+
+## Performance Model
+
+Use this model by setting:
+
+- performance model: `HTSEPerformanceModel`
+
+The HTSE performance model inherits from the electrolyzer base classes, so it is treated as a hydrogen-producing, dispatchable technology with an `electricity_in` input and a `hydrogen_out` output.
+
+```{figure} images/HTSE.png
+:alt: HTSE schematic
+:width: 100%
+:align: center
+```
+
+### Performance configuration parameters
+
+These are read from `performance_parameters` and `shared_parameters`.
+
+| Key | Type | Units | Description |
+| --- | --- | --- | --- |
+| `n_clusters` | int | unitless | Number of HTSE clusters. |
+| `cluster_rating_MW` | float | MW | Nameplate electrical rating per cluster. |
+| `nominal_heat_required` | float | kWh/kg | Nominal thermal energy required per kg of hydrogen. |
+| `nominal_electricity_required` | float | kWh/kg | Nominal electrical energy required per kg of hydrogen. |
+| `turndown_ratio` | float | unitless | Minimum fraction of rated hydrogen production required to stay on. |
+| `location` | str | n/a | `onshore` or `offshore`. Present in config but not used directly in the current performance calculation. |
+| `eol_eff_percent_loss` | float | percent | End-of-life efficiency loss setting. Present in config but not used directly in the current timestep energy balance. |
+| `uptime_hours_until_eol` | int | h | Hours of operation between replacement events. |
+| `include_degradation_penalty` | bool | n/a | Present in config but not used directly in the current timestep energy balance. |
+| `pressure_H2` | float | n/a | Hydrogen pressure setting. Present in config but not used directly in the current timestep energy balance. |
+| `size_mode` | str | n/a | Optional resizing mode inherited from the resizeable performance base class. |
+| `flow_used_for_sizing` | str | n/a | Required for non-default sizing modes. |
+| `max_feedstock_ratio` | float | unitless | Used when `size_mode = resize_by_max_feedstock`. |
+| `max_commodity_ratio` | float | unitless | Used when `size_mode = resize_by_max_commodity`. |
+
+### Performance inputs
+
+| Name | Shape | Units | Description |
+| --- | --- | --- | --- |
+| `electricity_in` | array[n_timesteps] | kW | Available electrical input. Added by the electrolyzer base class. |
+| `heat_in` | array[n_timesteps] | kW | Available thermal input. |
+| `n_clusters` | scalar | unitless | Number of HTSE clusters used to determine installed size. |
+| `cluster_size` | scalar | MW | Declared input in the component. Currently not used in the timestep calculation. |
+| `max_hydrogen_capacity` | scalar | kg/h | Used in resize-by-commodity sizing mode. |
+| `hydrogen_command_value` | array[n_timesteps] | kg/h | Optional hydrogen demand signal when `system_level_control` is enabled. |
+| `max_feedstock_ratio` | scalar | unitless | Inherited optional resize input. |
+| `max_commodity_ratio` | scalar | unitless | Inherited optional resize input. |
+
+### Performance outputs
+
+| Name | Shape | Units | Description |
+| --- | --- | --- | --- |
+| `hydrogen_out` | array[n_timesteps] | kg/h | Hydrogen production. |
+| `rated_hydrogen_production` | scalar | kg/h | Rated hydrogen output based on installed electrical size and `nominal_electricity_required`. |
+| `total_hydrogen_produced` | scalar | kg | Hydrogen produced over the simulated period. |
+| `annual_hydrogen_produced` | array[plant_life] | kg/year | Annualized hydrogen production repeated across plant life. |
+| `capacity_factor` | array[plant_life] | unitless | Simulated production relative to rated production. |
+| `electrolyzer_size_mw` | scalar | MW | Installed HTSE electrical nameplate size. |
+| `heat_demand` | array[n_timesteps] | kW | Requested HTSE thermal demand based on hydrogen demand. |
+| `electricity_demand` | array[n_timesteps] | kW | Reported electrical demand signal. In the current implementation this is set to installed electrical size in kW. |
+| `electricity_consumed` | array[n_timesteps] | kW | Electricity required by the current energy balance calculation. |
+| `water_demand` | array[n_timesteps] | kg/h | Water consumption based on hydrogen production stoichiometry. |
+| `efficiency` | scalar | unitless | Mean ratio of utilized input energy to available input energy over the simulation. |
+| `replacement_schedule` | array[plant_life] | unitless | Replacement events derived from `uptime_hours_until_eol`. |
+| `time_until_replacement` | scalar | h | Hours until replacement. |
+
+### Dispatch and sizing behavior
+
+Installed size is first inferred from:
+
+$$
+\text{electrolyzer\_size\_mw} = n_{clusters} \times cluster\_rating\_MW
+$$
+
+The model supports additional sizing modes inherited from the resizeable performance base class:
+
+- `normal`
+- `resize_by_max_feedstock`
+- `resize_by_max_commodity`
+
+In the current implementation:
+
+- `resize_by_max_feedstock` supports sizing from `electricity`
+- `resize_by_max_commodity` supports sizing from `hydrogen`
+
+When system-level control is enabled, hydrogen demand is taken from `hydrogen_command_value`. Otherwise, the model assumes demand equal to rated hydrogen production implied by installed electrical size.
+
+### Energy balance behavior
+
+The model forms:
+
+$$
+\text{total\_specific\_energy} = nominal\_heat\_required + nominal\_electricity\_required
+$$
+
+and computes a nominal heat-to-electricity ratio:
+
+$$
+\text{ratio\_heat\_elec\_nom} = \frac{nominal\_heat\_required}{nominal\_electricity\_required}
+$$
+
+Available heat is used first up to the requested `heat_demand`. The remaining required energy is supplied electrically when possible. Hydrogen production is then limited by the combined energy available and by the turndown threshold.
+
+```{note}
+The current implementation is intentionally simple and should be interpreted as a reduced-order plant representation, not a detailed SOEC stack model with thermal transients, degradation coupling, startup dynamics, or detailed balance-of-plant behavior.
+```
+
+## Cost Model
+
+Use this model by setting:
+
+- cost model: `HTSECostModel`
+
+The cost model is size-based and currently depends only on installed HTSE size.
+
+### Cost configuration parameters
+
+| Key | Type | Units | Description |
+| --- | --- | --- | --- |
+| `unit_capex` | float | USD/kW | Installed capital cost per kW of HTSE electrical size. |
+| `fixed_opex` | float, optional | USD/(kW*year) | Fixed annual operating cost per kW. |
+| `fixed_capex` | float, optional | USD/(kW*year) | Fallback value used to populate `fixed_opex` if `fixed_opex` is omitted. |
+| `cost_year` | int | year | Dollar year of the cost inputs. Defaults to `2025`. |
+
+### Cost inputs
+
+| Name | Shape | Units | Description |
+| --- | --- | --- | --- |
+| `electrolyzer_size_mw` | scalar | MW | Installed HTSE size from the performance model. |
+| `total_hydrogen_produced` | scalar | kg | Added by the electrolyzer cost base class, but not used directly in the current HTSE cost calculation. |
+| `electricity_in` | array[n_timesteps] | kW | Added by the electrolyzer cost base class, but not used directly in the current HTSE cost calculation. |
+
+### Cost outputs
+
+| Name | Shape | Units | Description |
+| --- | --- | --- | --- |
+| `CapEx` | scalar | USD | `unit_capex * electrolyzer_size_kw` |
+| `OpEx` | scalar | USD/year | `fixed_opex * electrolyzer_size_kw` |
+| `VarOpEx` | array[plant_life] | USD/year | Inherited base output. The current model does not set a nonzero variable operating cost. |
+| `cost_year` | scalar | year | Cost dollar year. |
+
+
diff --git a/docs/technology_models/images/HTSE.png b/docs/technology_models/images/HTSE.png
diff --git a/docs/technology_models/images/ThermalNucReactor-H2I.png b/docs/technology_models/images/ThermalNucReactor-H2I.png
diff --git a/docs/technology_models/nuclear.md b/docs/technology_models/nuclear.md
@@ -1,83 +1,81 @@
-# Nuclear power plant model
+# Nuclear power plant models
 
-The nuclear power plant model provides a simple, size-based performance model and a type-based cost model.
-Cost defaults are intended to be populated from literature, such as Quinn et al. (2023) on SMR LWR techno-economic analysis.
-See the paper here: [Quinn et al. (2023)](#references).
+H2Integrate currently includes two nuclear converter options:
 
-To use this model, set the performance model to `QuinnNuclearPerformanceModel` and the cost model to `QuinnNuclearCostModel` in your `tech_config`.
+- `QuinnNuclearPerformanceModel` with `QuinnNuclearCostModel` for a simple electricity-only nuclear plant
+- `SimpleThermalNuclearReactorPerformanceModel` with `SimpleThermalNuclearReactorCostModel` for a thermal reactor that can trade off electricity production and process heat delivery
 
-## Performance model
+The first model is based on Quinn et al. (2023). The second is a simplified thermal reactor representation intended for coupled workflows such as nuclear plus HTSE.
 
-The performance model limits electricity production by the rated capacity and an optional demand signal.
+## Quinn electricity-only nuclear model
+
+Use this model by setting:
+
+- performance model: `QuinnNuclearPerformanceModel`
+- cost model: `QuinnNuclearCostModel`
+
+### Performance behavior
+
+This model produces electricity only. It clips the commanded electricity output to the rated plant capacity and reports aggregate production metrics.
 
 **Inputs**
+
 | Name | Shape | Units | Description |
 | --- | --- | --- | --- |
 | `system_capacity` | scalar | kW | Rated electrical capacity. |
-| `electricity_set_point` | array[n_timesteps] | kW | Optional set point profile; defaults to rated capacity. |
+| `electricity_command_value` | array[n_timesteps] | kW | Requested electrical output profile. Defaults to `system_capacity`. |
 
 **Outputs**
+
 | Name | Shape | Units | Description |
 | --- | --- | --- | --- |
-| `electricity_out` | array[n_timesteps] | kW | Electricity produced, capped at `system_capacity`. |
-| `rated_electricity_production` | scalar | kW | Rated production (capacity). |
-| `total_electricity_produced` | scalar | kW*h | Sum of production over the simulation. |
-| `annual_electricity_produced` | array[plant_life] | kW*h/year | Annualized production. |
-| `capacity_factor` | array[plant_life] | unitless | Ratio of actual to maximum production. |
-| `replacement_schedule` | array[plant_life] | unitless | Placeholder replacement schedule (zeros). |
-| `operational_life` | scalar | yr | Operational life (defaults to plant life). |
+| `electricity_out` | array[n_timesteps] | kW | Electricity output after clipping to capacity. |
+| `rated_electricity_production` | scalar | kW | Rated plant capacity. |
+| `total_electricity_produced` | scalar | kW*h | Electricity produced over the simulated period. |
+| `annual_electricity_produced` | scalar | kW*h/year | Annualized electricity production. |
+| `capacity_factor` | scalar | unitless | Simulated production divided by maximum possible production. |
 
-## Cost model
+### Cost behavior
 
-The cost model uses direct cost parameters to compute capital and operating costs.
-It supports optional scaling of capex with size using a reference capacity and scaling exponent.
+The cost model applies:
 
-**Inputs**
-| Name | Shape | Units | Description |
-| --- | --- | --- | --- |
-| `system_capacity` | scalar | kW | Plant capacity used for cost scaling. |
-| `electricity_out` | array[n_timesteps] | kW | Output from performance model. |
+- capital cost from `capex_per_kw`
+- fixed O&M from `fixed_opex_per_kw_year`
+- variable O&M from `variable_opex_per_mwh`
+- optional capex scaling using `reference_capacity_kw` and `capex_scaling_exponent`
+
+**Cost parameters**
 
-**Cost parameters (tech_config)**
 | Key | Type | Description |
 | --- | --- | --- |
-| `system_capacity_kw` | float | Rated electrical capacity (kW). |
-| `capex_per_kw` | float | Capital cost per kW. |
-| `fixed_opex_per_kw_year` | float | Fixed O&M per kW per year. |
-| `variable_opex_per_mwh` | float | Variable O&M per MWh. |
-| `reference_capacity_kw` | float | Reference capacity for capex scaling (defaults to `system_capacity_kw`). |
-| `capex_scaling_exponent` | float | Capex scaling exponent (defaults to 1.0). |
-| `cost_year` | int | Dollar year for the input costs. |
-
-The capex calculation follows:
-
-$$
-C_{\text{capex}} = (c_{\text{capex}} \cdot (P / P_{\text{ref}})^{(k-1)}) \cdot P
-$$
-
-Where $c_{\text{capex}}$ is `capex_per_kw`, $P$ is plant capacity (kW), $P_{\text{ref}}$ is `reference_capacity_kw`, and $k$ is `capex_scaling_exponent`.
+| `system_capacity_kw` | float | Rated electrical capacity in kW. |
+| `capex_per_kw` | float | Capital cost in USD/kW. |
+| `fixed_opex_per_kw_year` | float | Fixed O&M in USD/(kW*year). |
+| `variable_opex_per_mwh` | float | Variable O&M in USD/MWh. |
+| `reference_capacity_kw` | float, optional | Reference capacity for capex scaling. Defaults to `system_capacity_kw`. |
+| `capex_scaling_exponent` | float | Scaling exponent applied to capex. Defaults to `1.0`. |
+| `cost_year` | int | Dollar year of the cost inputs. |
 
 **Outputs**
+
 | Name | Shape | Units | Description |
 | --- | --- | --- | --- |
-| `CapEx` | scalar | USD | Total capital expenditure. |
-| `OpEx` | scalar | USD/year | Fixed plus variable O&M. |
-| `VarOpEx` | array[plant_life] | USD/year | Variable O&M (repeated each year). |
-| `cost_year` | scalar | year | Dollar year of costs. |
+| `CapEx` | scalar | USD | Total capital cost. |
+| `OpEx` | scalar | USD/year | Fixed annual O&M. |
+| `VarOpEx` | array[plant_life] | USD/year | Variable annual O&M repeated across plant life. |
 
-## Example tech_config
+### Example `tech_config`
 
 ```yaml
 technologies:
   nuclear:
     performance_model:
-      model: "QuinnNuclearPerformanceModel"
+      model: QuinnNuclearPerformanceModel
     cost_model:
-      model: "QuinnNuclearCostModel"
+      model: QuinnNuclearCostModel
     model_inputs:
       performance_parameters:
         system_capacity_kw: 300000.0
-        capacity_factor: 0.9
       cost_parameters:
         system_capacity_kw: 450000.0
         capex_per_kw: 6000.0
@@ -88,6 +86,7 @@ technologies:
         cost_year: 2023
 ```
 
+
 ## References
 
 - Quinn, J. et al., 2023. Small modular reactor light water reactor techno-economic analysis. Applied Energy 120669. https://doi.org/10.1016/j.apenergy.2023.120669