Multi-stage setup

This section describes the available features, inputs and model components related to formulating and solving multi-stage investment planning problems. Two different types of multi-stage problems can be setup:

Perfect foresight: A single multi-stage investment planning problem that simultaneously optimizes capacity and operations across all specified investment stages
Myopic: Sequential solution of single-stage investment planning for each investment stage, where capacity additions and retirements from the previous stages are used to determine initial (or existing) capacity at the beginning of the current stage.

The table below summarizes the key differences in the two model setups.

	Perfect foresight	Myopic
No. of optimization problems solved	1	Equal to number of investment stages
Objective function cost basis	Net present value	Annualized costs
Price/dual variable information available?	No	Yes

Additional inputs needed for multi-stage modeling

Input data files

Instead of one set of input files, there is one directory of input files that needs to be provided for each planning period or stage (e.g., “inputs/inputs_p1/” for the first period “inputs/inputs_p2/” for the second period, etc.). Below we list the additional parameters that must be provided in the corresponding stage-specific input files to instantiate a multi-stage planning problem.

	Resourcemultistagedata.csv files
Min_Retired_Cap_MW	Minimum capacity in MW that must retire in this planning stage. Note that for the co-located VRE-STOR module, this value represents the grid connection component.
Min_Retired_Energy_Cap_MW	Minimum energy capacity in MW that must retire in this planning stage. Note that for the co-located VRE-STOR module, this value represents the storage component.
Min_Retired_Charge_Cap_MW	Minimum charge capacity in MW that must retire in this planning stage.
Lifetime	The operational lifespan in years of this technology after which it must be retired.
Capital_Recovery_Period	The technology-specific period in years over which initial capital costs must be recovered. Note that for the co-located VRE-STOR module, this value represents the grid connection component.
WACC	The technology-specific weighted average cost of capital. Note that for the co-located VRE-STOR module, this value represents the grid connection component.
Contribute_Min_Retirement	{0, 1}, Flag to indicate whether the (retrofitting) resource can contribute to the minimum retirement requirement.

	co-located VRE-STOR resources only
Min_Retired_Cap_Inverter_MW	Minimum inverter capacity in MW AC that must retire in this plannig stage.
Min_Retired_Cap_Solar_MW	Minimum solar PV capacity in MW DC that must retire in this plannig stage.
Min_Retired_Cap_Wind_MW	Minimum wind capacity in MW AC that must retire in this plannig stage.
Min_Retired_Cap_DischargeDC\MW	Minimum storage DC discharge capacity that must retire in this planning stage with `STOR_DC_DISCHARGE = 2`.
Min_Retired_Cap_ChargeDC\MW	Minimum storage DC charge capacity that must retire in this planning stage with `STOR_DC_CHARGE = 2`.
Min_Retired_Cap_DischargeAC\MW	Minimum storage AC discharge capacity that must retire in this planning stage with `STOR_AC_DISCHARGE = 2`.
Min_Retired_Cap_ChargeAC\MW	Minimum storage AC charge capacity that must retire in this planning stage with `STOR_AC_CHARGE = 2`.
Capital_Recovery_Period_DC	The technology-specific period in years over which initial capital costs for the inverter component must be recovered.
Capital_Recovery_Period_Solar	The technology-specific period in years over which initial capital costs for the solar PV component must be recovered.
Capital_Recovery_Period_Wind	The technology-specific period in years over which initial capital costs for the wind component must be recovered.
Capital_Recovery_PeriodDischargeDC	The technology-specific period in years over which initial capital costs for the storage DC discharge component must be recovered when `STOR_DC_DISCHARGE = 2`.
Capital_Recovery_PeriodChargeDC	The technology-specific period in years over which initial capital costs for the storage DC charge component must be recovered when `STOR_DC_CHARGE = 2`.
Capital_Recovery_PeriodDischargeAC	The technology-specific period in years over which initial capital costs for the storage AC discharge component must be recovered when `STOR_AC_DISCHARGE = 2`.
Capital_Recovery_PeriodChargeAC	The technology-specific period in years over which initial capital costs for the storage AC charge component must be recovered when `STOR_DC_CHARGE = 2`.
WACC_DC	The line-specific weighted average cost of capital for the inverter component.
WACC_Solar	The line-specific weighted average cost of capital for the solar PV component.
WACC_Wind	The line-specific weighted average cost of capital for the wind component.
WACC_Discharge_DC	The line-specific weighted average cost of capital for the discharging DC storage component with `STOR_DC_DISCHARGE = 2`.
WACC_Charge_DC	The line-specific weighted average cost of capital for the charging DC storage component with `STOR_DC_CHARGE = 2`.
WACC_Discharge_AC	The line-specific weighted average cost of capital for the discharging AC storage component with `STOR_AC_DISCHARGE = 2`.
WACC_Charge_AC	The line-specific weighted average cost of capital for the charging AC storage component with `STOR_AC_CHARGE = 2`.

	Network.csv
Line_Max_Flow_Possible_MW	The maximum transmission capacity of the line, as opposed to Line_Max_Reinforcement_MW which now specifies the maximum expansion to the line in one stage.
Capital_Recovery_Period	The line-specific period in years over which initial capital costs must be recovered.
WACC	The line-specific weighted average cost of capital.

Allowing retrofitted capacity to not contribute to minimum retirement requirements (`myopic=0` only)

Special considerations must be taken into account when utilizing the retrofit module alongside multi-stage planning, particularly when using a non zero value for the Min_Retired_Cap_MW column in the Resource_multistage_data.csv file.

When assigning a non-zero value to the Min_Retired_Cap_MW column in the Resource_multistage_data.csv file, the user can specify whether the model should consider the retrofitted capacity to contribute to the minimum retirement requirement. This is done by setting the Contribute_Min_Retirement column to 1 for the retrofit options in the same retrofit cluster (i.e., same Retrofit_Id).
By default, the model assumes that retrofitted capacity contributes to fulfilling minimum retirement requirements.
Should users wish to exclude retrofitted capacity from contributing to minimum retirement requirements, they must set the Contribute_Min_Retirement column to 0 for all retrofit options within the same retrofit cluster (i.e., sharing the same Retrofit_Id).
It's important to note that this additional functionality is not currently supported when myopic=1. In this case, the retrofit options are only allowed to contribute to the minimum retirement requirement.

Example 1: Retrofitted capacity is allowed to contribute to the minimum retirement requirement (i.e., retrofit options in the same cluster (Retrofit_Id = 1) all have Contribute_Min_Retirement = 1):

Thermal.csv

Resource          │ Zone  | Retrofit | Can_Retrofit | Retrofit_Id | Retrofit_Efficiency
String            │ Int64 | Int64    | Int64        | Int64       | Float64
─────────────────-┼───────┼─────────────────────────┼────────────-┼────────────────────
coal_1            │ 1     │ 0        │ 1            │ 1           │ 0
20_NH3_retrofit_1 │ 1     │ 1        │ 0            │ 1           │ 0.85
20_NH3_retrofit_2 │ 1     │ 1        │ 0            │ 1           │ 0.85

Resource_multistage_data.csv

Resource          │ Min_Retired_Cap_MW | Contribute_Min_Retirement
String            │ Float64            | Float64 
─────────────────-┼────────────────────┼──────────────────────────
coal_1            │ 4500               │ 0
20_NH3_retrofit_1 │ 0                  │ 1                         <---------
20_NH3_retrofit_2 │ 0                  │ 1                         <---------

Example 2: Retrofitted capacity is not allowed to contribute to the minimum retirement requirement (i.e., none of the retrofit options in the same cluster (Retrofit_Id = 1) contribute to the minimum retirement requirement (myopic=0)):

Thermal.csv: same as Example 1.

Resource_multistage_data.csv

Resource          │ Min_Retired_Cap_MW | Contribute_Min_Retirement
String            │ Float64            | Float64
─────────────────-┼────────────────────┼──────────────────────────
coal_1            │ 4500               │ 0
20_NH3_retrofit_1 │ 0                  │ 0                         <---------
20_NH3_retrofit_2 │ 0                  │ 0                         <---------

And the case where some retrofit options contribute to the minimum retirement requirement and some do not is not currently supported and will be addressed in a future release.

Warning

If New_Build and Can_Retire are both set to 0, the model will not transfer built capacity from one stage to the next, but will instead set capacity to the value of existing capacity from the input files for each stage. Therefore, the user must ensure that the capacity is correctly set in the input files for each stage. Not following this guideline may result in incorrect or unexpected results, particularly when setting a a non-zero value for the Min_Retired_Cap_MW parameter.

Settings Files

A separate settings.yml file includes a list of parameters to be specified to formulate the multi-stage planning model.

	multi_stage_settings.yml
NumStages	The number of model investment planning stages.
StageLengths	A list of lengths of each model stage in years (e.g., [10, 10, 10] for three stages each of length 10). Note that stages could be defined to be of varying length.
Myopic	0 = perfect foresight, 1 = myopic model (see above table)
ConvergenceTolerance	The relative optimality gap used for convergence of the dual dynamic programming algorithm. Only required when Myopic = 0
WACC	Rate used to discount non-technology-specific costs from stage to stage (i.e., the “social discount rate”).
WriteIntermittentOutputs	(valid if Myopic = 1) 0 = do not write intermittent outputs, 1 = write intermittent output.

	time_domain_reduction_settings.yml
MultiStageConcatenate	Designates whether to use time domain reduction for the full set of input data together (1) or to reduce only the first stage data and apply the returned representative periods to the rest of the input data (0).