Mid-term hydrothermal coordination¶
As discussed in previous sections the simulations depends on exogenous storage level profiles. These profiles have to be cogerent with the rest of the input parameters in order to ensure both the feasibility of the problem and accurate results.
In many cases, collecting accurate and reliable historical storage levels and profiles in form of hourly timeseries might be a difficult or close to impossible task. In future scenarios storage levels are usually forecasted based on the historical data. The lack of such data also impacts the accurate modelling of such scenarios. In systems with high shares of hydro dams (HDAM) and pumped hydro storage (HPHS) units, such as Norway and Albania, this might have a huge impact on the overall results of the simulation.
In order to avoid this, Dispa-SET’s Midterm Hydro-Thermal Scheduling (MTS) module represents a simplified version of the original MILP unit commitment and power dispatch model. This version is a simplified version of the linear programming formulation which allows perfect foresight and allocation of water resources for the whole optimization period and not only for the tactical horizon of each optimization step. This module enables quick calculation (later also referring as allocation) of reservoir levels which are then used as guidance curves (minimum level constraints) in one of the four main Dispa-SET formulations. The main options are:
- No-MTS, in which historical curves are used,
- Zonal-MTS, in which MTS is run for each Zone individually,
- Regional-MTS, in which MTS is run for two or more Zones from the selected region simultaneously.
This section describes the above options available in the Dispa-SET. It is worthwhile to note that each MTS method and/or modelling formulation can be applied to the same input dataset. This allows comparing the various methods in terms of computational efficiency, but also in terms of accuracy. Graphical summary of MTS options is available in Figure:
The MTS optimization (process) is being executed in the preprocessing phase. Here the simplified LP optimization estimates the reservoir levels for the entire year. These newly computed reservoir levels are then imposed as minimum level constraint used in the last time interval of the rolling horizon. As preprocessing includes LP optimization, it might take a while to complete and will be highly dependent on the number of selected zones (the more zones are selected the longer it will take to build the model). Depending on the operating system, command prompt may pop-up and interrupt other processes several times.
NO-MTS (Historical Curves)¶
HISTORICAL is the standard formulation of the Dispa-SET model. All reservoir levels are imposed as external timeseries in form of scaled reservoir levels (in range from 0 - 1). These reservoir levels are used as minimum level constraint in the last time interval of the rolling horizon.
ZONAL formulation can be used in two ways: 1) If not specified otherwise (default option), MTS will be run for each of the selected zones individually. For a system of four zones configured as shown in figure 1, each of the zones A, B, C & D MTS will be run once. In this formulation NTC capacities are not considered. Instead, default cross border flows from the database are used. . 2) Zones where MTS should be run can also be specified in the list of zones. In this case, MTS module will only be run in the specified zones. In our example with four zones, zones A, B & D are selected for the MTS, while zone C keeps the default values from the database.
REGIONAL formulation can be used in the same way as zonal formulation.
1) If not specified otherwise, MTS will be run once, for the whole region at once. For the system of four zones configured as shown in figure 1, zones A, B, C & D will be regarded as a region. In this formulation MTS will compute reservoir levels based on additional criteria such as available net transfer capacities (NTC) instead of historical cross border flows (CBF).
2) Region where MTS should be run can also be specified in the list of zones contained within one region. In this case MTS module will be run only in the selected region. In our example zones A, B & D. Zone C keeps the default values from the database. This formulation generates even more accurate results compared to the zonal formulation but might increase the memory usage and computation time significantly.
How to call MTS¶
MTS module is called automatically if the relevant parameters indicate the use of it. During the build phase Dispa-SET will read the MTS parameters from the Config file (either .xlsx or .yml), execute the MTS module and build SimData with newly computed reservoir levels. Additional options also allow selection of specific zones and ploting the difference between the historical and newly computed reservoir levels (this is only useful for debugging purposes). The latter is triggered if the build_simulation functions is called with the flag mts_plot=True.
Selection of MTS options inside the Config file:
|Hydro scheduling horizon||HydroSchedulingHorizon:|
|Initial/Final reservoir level||InitialFinalReservoirLevel:|
||ReservoirLevelInitial: & ReservoirLevelFinal:|
Computing reservoir levels by using the MTS module increases the accuracy of HDAM and HPHS units and avoids infeasible ramping up/down rates proposed by the historical levels. A good example of one such case is when the difference between initial and final reservoir levels is higher than the sum of all the inflows during that time horizon.
Lets assume that ReservoirLevelInital = 1 MWh , ReservoirLevelFinal = 30 MWh, Pmax = 1 MW, InFlows = 1 MW per hour which totals 24 MWh for horizon length of one day. In this case the reservoir cannot reach the storage target as it is constrained by the generation capacity.
This would produce infeasible solution which would then have a price of water slackof 100€/MWh imposed on the difference between historical and calculated reservoir levels in the last time interval of the rolling horizon (an imaginary well that fills the reservoir). In our example this would then amount to 30MWh – 1MWh – 24MWh = 5 MW *100 €/MWh = 500€.
This might still be the case even if MTS is turned on. Thus, Hydro scheduling horizon option inside the Config files provides additional flexibility for running the MTS:
- Stop-date driven runs the MTS only between the selected start and stop dates, while
- Annual runs the MTS between 01.01. and 31.12. of the selected year.
Initial/Final reservoir levels can be imposed as TRUE/FALSE statement. When TRUE Initial and Final reservoir levels can be imposed externally and should always be in range between 0 and 1 (0 completely empty reservoir and 1 for 100% full reservoir). This option will override initial and final reservoir levels for all hydro units in all selected zones. This might be useful when analysing countries/zones with data scarcity. When FALSE historical values for Initial and Final reservoir levels will be considered.