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NPV: Avoid excessive candidate capacity during investment #1271

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4f2aadc
Don't use `Option` for `max_capacity` in most places
alexdewar May 1, 2026
83fb8a6
Use `max_capacity` cf. value of capacity var for NPV
alexdewar May 1, 2026
3c9ae3f
Fix: Recalculate demand limiting capacity every round to constrain ca…
alexdewar May 1, 2026
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14 changes: 11 additions & 3 deletions src/simulation/investment.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -759,14 +759,22 @@ fn select_best_assets(
// Appraise all options
let mut outputs_for_opts = Vec::new();
for asset in &opt_assets {
// For candidates, determine the maximum capacity that can be invested in this round,
// according to the tranche size and remaining capacity limits.
// For candidates, determine the maximum capacity that can be invested in this round.
// This is whichever is the smallest of the tranche size (based on demand limiting
// capacity before investment), the remaining available capacity for the candidate and
// the demand limiting capacity recalculated based on demand unserved by the other
// selected assets.
let max_capacity = (!asset.is_commissioned()).then(|| {
let tranche_capacity = asset
.capacity()
.apply_limit_factor(model.parameters.capacity_limit_factor);
let dlc = AssetCapacity::from_capacity(
get_demand_limiting_capacity(&model.time_slice_info, asset, commodity, &demand),
asset.unit_size(),
);
let remaining_capacity = remaining_candidate_capacity[asset];
tranche_capacity.min(remaining_capacity)

tranche_capacity.min(dlc).min(remaining_capacity)
});
Comment on lines 761 to 778
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Copilot AI May 1, 2026

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max_capacity (including the new demand-limiting-capacity recomputation) is calculated before the group-id de-duplication check. If there are many identical candidates in the same group, this recomputes DLC/tranche/remaining for assets that will be skipped anyway. Consider moving the group check before computing max_capacity (or computing max_capacity only for the representative asset) to avoid unnecessary work in large models.

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// Skip any assets from groups we've already seen
Expand Down
12 changes: 8 additions & 4 deletions src/simulation/investment/appraisal.rs
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Expand Up @@ -69,13 +69,14 @@ impl AppraisalOutput {
/// Create a new `AppraisalOutput`
fn new<T: MetricTrait>(
asset: AssetRef,
capacity: AssetCapacity,
results: ResultsMap,
metric: Option<T>,
coefficients: Rc<ObjectiveCoefficients>,
) -> Self {
Self {
asset,
capacity: results.capacity,
capacity,
activity: results.activity,
unmet_demand: results.unmet_demand,
metric: metric.map(|m| Box::new(m) as Box<dyn MetricTrait>),
Expand Down Expand Up @@ -252,7 +253,7 @@ impl MetricTrait for NPVMetric {}
fn calculate_lcox(
model: &Model,
asset: &AssetRef,
max_capacity: Option<AssetCapacity>,
max_capacity: AssetCapacity,
commodity: &Commodity,
coefficients: &Rc<ObjectiveCoefficients>,
demand: &DemandMap,
Expand All @@ -276,6 +277,7 @@ fn calculate_lcox(

Ok(AppraisalOutput::new(
asset.clone(),
results.capacity,
results,
cost_index.map(LCOXMetric::new),
coefficients.clone(),
Expand All @@ -290,7 +292,7 @@ fn calculate_lcox(
fn calculate_npv(
model: &Model,
asset: &AssetRef,
max_capacity: Option<AssetCapacity>,
max_capacity: AssetCapacity,
commodity: &Commodity,
coefficients: &Rc<ObjectiveCoefficients>,
demand: &DemandMap,
Expand Down Expand Up @@ -320,13 +322,14 @@ fn calculate_npv(

Ok(AppraisalOutput::new(
asset.clone(),
max_capacity,
results,
Some(NPVMetric::new(profitability_index)),
coefficients.clone(),
))
Comment on lines 323 to 329
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Copilot AI May 1, 2026

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In calculate_npv, AppraisalOutput::new is being given max_capacity rather than the optimiser's chosen results.capacity. This makes the output capacity inconsistent with the activity/unmet_demand/metric (which are all based on results), and can also cause AppraisalOutput::is_valid() to treat a solution with results.capacity == 0 as valid if max_capacity > 0 (potentially selecting an asset that doesn't actually serve demand). Use results.capacity for the output capacity, or alternatively change the optimisation formulation so results.capacity is forced to equal max_capacity if that is the intended installed capacity for NPV appraisal.

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}

/// Appraise the given investment with the specified objective type
/// Appraise the given investment with the specified objective type.
///
/// # Returns
///
Expand All @@ -341,6 +344,7 @@ pub fn appraise_investment(
coefficients: &Rc<ObjectiveCoefficients>,
demand: &DemandMap,
) -> Result<AppraisalOutput> {
let max_capacity = max_capacity.unwrap_or(asset.capacity());
let appraisal_method = match objective_type {
ObjectiveType::LevelisedCostOfX => calculate_lcox,
ObjectiveType::NetPresentValue => calculate_npv,
Expand Down
5 changes: 2 additions & 3 deletions src/simulation/investment/appraisal/constraints.rs
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Expand Up @@ -16,11 +16,10 @@ use indexmap::IndexMap;
pub fn add_capacity_constraint(
problem: &mut Problem,
asset: &AssetRef,
max_capacity: Option<AssetCapacity>,
max_capacity: AssetCapacity,
capacity_var: Variable,
) {
let capacity_limit = max_capacity.unwrap_or(asset.capacity());
let capacity_limit = match capacity_limit {
let capacity_limit = match max_capacity {
AssetCapacity::Continuous(cap) => cap.value(),
AssetCapacity::Discrete(units, _) => units as f64,
};
Expand Down
4 changes: 2 additions & 2 deletions src/simulation/investment/appraisal/optimisation.rs
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Expand Up @@ -95,7 +95,7 @@ pub struct ResultsMap {
fn add_constraints(
problem: &mut Problem,
asset: &AssetRef,
max_capacity: Option<AssetCapacity>,
max_capacity: AssetCapacity,
commodity: &Commodity,
variables: &VariableMap,
demand: &DemandMap,
Expand Down Expand Up @@ -127,7 +127,7 @@ fn add_constraints(
/// asset has a defined unit size.
pub fn perform_optimisation(
asset: &AssetRef,
max_capacity: Option<AssetCapacity>,
max_capacity: AssetCapacity,
commodity: &Commodity,
coefficients: &ObjectiveCoefficients,
demand: &DemandMap,
Expand Down
12 changes: 6 additions & 6 deletions tests/data/simple_npv/assets.csv
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Expand Up @@ -5,12 +5,12 @@ asset_id,process_id,region_id,agent_id,group_id,commission_year,decommission_yea
3,GASCGT,GBR,A0_ELC,,2020,,2.43
4,RGASBR,GBR,A0_RES,,2020,2030,2900.0
5,RELCHP,GBR,A0_RES,,2020,2035,399.98
6,RELCHP,GBR,A0_RES,,2030,,3290.2365652888325
6,RELCHP,GBR,A0_RES,,2030,,3255.838405876481
7,GASCGT,GBR,A0_ELC,,2030,,33.820477802912976
8,GASPRC,GBR,A0_GPR,,2030,,879.1648830751317
9,GASDRV,GBR,A0_GEX,,2030,,923.1231272288879
10,RGASBR,GBR,A0_RES,,2040,,4011.65737547648
11,RELCHP,GBR,A0_RES,,2040,,802.3314750952961
12,GASCGT,GBR,A0_ELC,,2040,,3.7231090668357614
13,GASPRC,GBR,A0_GPR,,2040,,94.9477829022087
14,GASDRV,GBR,A0_GEX,,2040,,99.6951720473196
10,RGASBR,GBR,A0_RES,,2040,,4011.6573754764804
11,RELCHP,GBR,A0_RES,,2040,,755.8189695999995
12,GASCGT,GBR,A0_ELC,,2040,,3.7231090668357543
13,GASPRC,GBR,A0_GPR,,2040,,94.94778290220857
14,GASDRV,GBR,A0_GEX,,2040,,99.69517204731937
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