The component Priority
The Priority component can be used to determine the mode of operation of an energy system by setting a switch-on sequence for the operation of controllable systems. For this purpose, the priorities of the plants are selected according to their operating sequence in the input form. A distinction is made between suppliers (priority of generation) and demands (priority of feed-in).
Component Template
The Priority.e-ctpl component template is located in the Component template library folder Operational Side Conditions.
Integration Into a Scheme
The following figure shows variant 2 from tutorial 05.
You can find other examples of the use of the Priority component in the Tutotorial 60 Priority and operational optimization and in the articles on storage loading and unloading strategies and on controlling performance of an energy system consisting of a CHP unit, a hot water boiler, and a power generator.
How the Component Works
The component Priority works with the objective functions of operational optimization Operating costs, CO2 emissions, and Primary energy. Priority is only considered in the operational optimization. Because the systems are operated according to the switch-on sequence, true optimization cannot be achieved; for example, CO2 emissions cannot be reduced as they otherwise could be. However, if, for example, you control only the heating supply via a Priority, the cooling supply—which is not involved in this process—will continue to be optimized according to the objective function.
The component Priority does not work with the objective fuction User defined and with the objective functions of strutural optimization Investment costs, Annualized total cost, and Net present value. Structural optimization does not take the Priority into account because the optimal structure of the power system cannot be determined based on a given control strategy. If you still want to take certain conditions into account during structural optimization, you can use Programmable Controls for this purpose.
In the form of the component Priority, under the tabs Input data → Suppliers and demands, you can specify the ranking of the operation of the individual components.
Because the Priority component specifies the operating mode and thus the control of the system, no future steps need to be considered in the simulation.
Priority 1 is the highest priority. Priority 2 is the second highest priority and so on. If two components have the same priority they are treated the same.
Each Priority component refers to only one Kind of energy, which is to be selected first in the form (see the following figure).
The multi-column forms are used to assign suppliers (producers) and demands (consumers). Storages can be selected in both categories.
In the first column, select the components of the grid. You can 
Remove the entry using the 
menu button. In the last column, select the Priority from the drop-down list.
Start defining the switch-on sequence for the suppliers by choosing the priority of the generation components (e.g., heat generation, electricity generation).
Suppliers (generators)
Suppliers in the Priority component are not only the supplier components but also the other energy generating components. The supplier component with the highest priority shall be operated as long and as often as possible up to its capacity limit, irrespective of the cost. Only when the first component is running at its maximum and cannot meet the demand, the second component starts its operation and so on.
The lower the priority (and the higher the priority number), the lower the virtual revenue of the supplier component operation.
Demands (consumers)
In the usual simulation cases, the demands are defined. This means, for example, that in the Heat demand component there is a time series for the demand; and the demand is not a free variable in the simulation. In these cases, no demand is entered in the Priority component.
If, on the other hand, there are variable, flexible demands, they must be prioritized in the Priority component. These include, for example, Emergency Coolers and—if a variable Heat Demand was selected in the component form—also a Heat Demand (see following figures).
If demands (consumptions) are taken into account in the Priority (e.g., heat usage or steam usage), assign them the priorities Avoid feed-in or Feed-in by priority . . .
The restrictive option Avoid feed-in leads—regardless of the costs—to the avoidance of the feed-in of energy into this demand. This restriction is not absolute because even a consumer for which this option has been chosen can be supplied with energy if no other solution is found in the system.
Storages and Networks
Storages (storage devices) are interpreted as suppliers when they supply energy, i.e., they are discharged. Storages are interpreted as demands when they are charged. These two modes can be viewed independently of each other. For this reason there are two ways of entering priorities for storages and networks: first the priority as a supplier and second as a demand fed by priority (feed-in by priority).
A storage can normally be placed between other suppliers in the priority list. In the switch-on sequence of the demands, a storage can be regarded as a variable demand when it is charged.
A CHP unit has Priority 1, a storage has Priority 2, and a boiler has Priority 3: The CHP runs as much as possible, the storage is only discharged when the capacity of the CHP has been exhausted, and the boiler is only started last when the CHP and the storage together do not supply enough energy.
Further Information for Experts: Virtual Costs
In the background of the calculation of the optimization problem, the Priority component acts without the user having to know this process in detail. However, if several Priority components are used in one scheme, a more detailed knowledge of the operation is required. For this purpose, the principle of virtual costs underlying the component is described below.
The virtual costs and revenues (penalty and reward) only influence the optimization of operation and are not included in the economic evaluation.
For example, the operation of the supplier component with the highest Priority 1 generates higher virtual revenues per kilowatt-hour of energy generated than the operation of the supplier component with Priority 2.
The values stored for the suppliers are treated as a virtual reward, while those for the demands are treated as a virtual penalty:
| Priority | Component | Optimization Influence in EUR/kWh (Operating Costs) | Optimization Influence in kWh/kWh (Primary Energy) | Optimization Influence in kg/kWh (CO2 Emissions) |
|---|---|---|---|---|
| Priority 1 | supplier 1 | virtual revenues: 80 | virtual revenues: 80 | virtual revenues: 8 |
| Priority 2 | supplier 2 | virtual revenues: 70 | virtual revenues: 70 | virtual revenues: 7 |
| Priority 3 | supplier 2 | virtual revenues: 60 | virtual revenues: 60 | virtual revenues: 6 |
| Avoid feed-in | demand 1 | virtual costs: 85 | virtual costs: 85 | virtual costs: 8,5 |
| Feed-in by priority 1 | demand 2 | virtual costs: 75 | virtual costs: 75 | virtual costs: 7,5 |
| Feed-in by priority 1-2 | demand 3 | virtual costs: 65 | virtual costs: 65 | virtual costs: 6,5 |
This table can be continued in steps of -10 EUR, -10 kWh/kWh, or -1 kg/kWh, respectively. In the optimization, the complete avoidance of energy supply to a certain demand (avoid feed-in) is achieved by allocating this demand with particularly high virtual costs per kilowatt-hour consumed. With the second option Feed-in by priority 1, the virtual cost of energy consumption is slightly lower. In fact, the virtual costs of a consumption Feed-in by priority 1 are slightly lower than the virtual revenues of a supplier with Priority 1 etc. Therefore, demands that are supplied by a certain priority are only covered by components with a higher priority.
The virtual costs of 85 EUR/kWh for the consumption of the component for which Avoid feed-in has been defined (demand 1) are higher than the maximum possible revenues for a supplier so that feed-in is avoided in any case.
Demand 2, Feed-in by priority 1, is only allocated with virtual costs of 75 EUR/kWh, while supplier 1 with Priority 1 is rewarded with 80 EUR/kWh of virtual revenue. It is advantageous for the system to operate supplier 1 to cover demand 2 because the virtual net revenue is 5 EUR/kWh.
This is not the case with supplier 2: because this generates virtual revenues of only 70 EUR/kWh with Priority 2, but demand 2 causes virtual costs of 75 EUR/kWh, the generation of energy for demand 2 by supplier 2 is not worthwhile and is therefore prevented.
