Hydro Composite Reservoir Table
Use of Composite Reservoirs is an optional extension to the standard Hydro Shaping Logic of Aurora. It allows treatment of systems that have both seasonal hydro storage capability and significant flexibility and discretion on timing and pricing of generation. The intent is to allow representation of the value of stored energy to be reflected in the hydro pricing and operations logic. It may be appropriate for use when modeling systems where the dispatch and pricing of hydro resources plays a significant role in marginal price determination.
The logic is activated by including a Hydro Composite Reservoir table in the study. Additionally, the Hydro Vectors table will need to include the optional Composite Reservoir column which instructs the hydro sethydro set to use a composite reservoir for operations and pricing. Operationally, sets of individual hydro resources are tied to the composite reservoirs through hydro set composition. When a hydro set points to a valid composite reservoir, each resource using that hydro set is defined to be a member of the reservoir. Similarly to the standard logic which assumes that all units in a hydro set participate proportionally in the energy availability for a set, the assumption is made that each reservoir unit shares proportionally in the composite reservoir capability. The hourly shape parameter from the Hydro Vectors input is still used to generate an hourly availability profile, however the proportional load following option is unconditionally used for any hydro set using a composite reservoir. The resulting shape profile is essentially treated as the reservoir maximum capability in an hour, however this is subject to adjustment for minimum flow constraints or to avoid unnecessary spill. Note also that only the shape factor is used in the hydro shaping profile logic for composite reservoirs. Instantaneous min /max, sustained peaking limits, minimum energy, and energy shift options are not currently applied.
In general terms the composite reservoir logic works as follows:
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At the beginning of each hour the current state of the reservoir and inputs described in #1 below are used to determine the generation potential to each content point specified in #2 below. Minimum bypass spill and minimum generation requirements to meet minimum flow targets are also calculated. Since beginning content levels are integral to study continuity, in a non-hourly study estimates are also made for inflow, generation, spill and losses in the interval of un-sampled hours to derive an estimated beginning content level.
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The energy availabilities to each content point are used in conjunction with the hourly Hydro Shaping Logic to determine the incremental hourly capability for each price segment within the reservoir. As noted above, proportional load following is forced in the hydro shaping logic for composite reservoir hydro sets.
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The incremental composite reservoir capability at each pricing point is allocated to each unit in its member hydro set proportional to unit availability. A dispatch segment (using the heat rate curve structure) is created for each point. The segment dispatch prices are based on a combination of input price, shadow resources, and bid adders or factors.
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Any minimum generation requirement is allocated to member resources, removed from segment dispatchable capability, and treated as must-run in the dispatch.
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Post-dispatch, an energy balance is used to determine reservoir ending contents.
NOTE: When using composite reservoirs in a study, it is recommended that a fairly dense dispatch sample be used and that at least all days and all weeks be included.
NOTE: A dispatch segment will be created for each price curve used for the reservoir for each participating hydro resource. There may be a run time impact dependent on data configuration. For example, if a composite reservoir resource set consists of 1000 units and 5 price curves are used, that will create an additional 4000 dispatch segments for the dispatch and accounting logic. Run time impacts may be reduced by eliminating unneeded granularity in resource/unit definition. Individual hydro resource dispatch segment structure and results will be output to the Resource output tables when segment level reporting is selected.
Data Structure
There are two types of data structures used to setup a composite reservoir:
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Composite Storage Reservoir
These inputs will have various definitions in the Record Type column with the data structure stored in the Value column. Most of these inputs are in the form of energy content (MWh) and include items such as maximum and minimum storage, energy inflows, minimum flow, required bypass spill levels and losses due to evaporation, leakage, etc. All of these inputs are time-series compatible.
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Pricing Function
These inputs will have Record Type = Price Function and define hydro energy pricing as a function of reservoir storage level using the data entered in pricing related columns (e.g. Function Content, Function Price, Shadow Resource, Price Adder and Price Factor). This structure can be thought of as a series of temporal price curves drawn through reservoir energy content levels. The pricing curves allow control of how much energy is generated from a system at different points of time and at what price. In any time period, these curves need to be monotonically increasing in price with decreasing content level. There is no limit on the number of curves used, however, each composite reservoir defined in #1 above requires at least one of these pricing structures. Note also that model run time may be affected by the number of curves used.
Each composite reservoir is assigned to a hydro set in the Hydro Vectors table via the Composite Reservoir column.
NOTE: An input table Quick View sorted first by ID and then by Record Type will make working with this table easier.
NOTE: Hydro Composite Reservoirs are not currently compatible with Risk or Commitment Optimization study types.
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Hydro Composite Reservoir Table
