Basics of Structural Optimization
In structural optimization, not only the operation of the energy system is optimized, but also the size of selected plants. In this way, an appropriate dimensioning can be determined to support strategic decisions on an investment in new plants. Optimum values, for example, for CHP and absorption chillers in combined heat, power, and cooling systems or for photovoltaic systems and storages in stand-alone networks can be determined by structural optimization.
in the component ribbon (Features group, see the following figure). 
Three additional input fields appear in the component’s form (see the following figure).
First, determine whether the purchase and Installation of the plant is mandatory. If it is not mandatory, the degree of freedom remains in the optimization not to install the plant if the investment is not worthwhile.
Limit the possible power range of the plant by specifying the Minimum and Maximum nominal power.
You can read in a separate article how the Input data for the structural optimization components are entered.
Simulation Steps
For a single Simulation node, simulation with structural optimization components does not differ from conventional simulations in terms of handling. However, a two-stage optimization is carried out within the program:
The exact simulation procedure is described in the linked article.
Structural Optimization Settings
In the Simulation form under Settings → Structural optimization → Parameters, make settings for structural optimization within the simulation node selected in the Project explorer. These settings are saved in the project.
Use the Mode drop-down menu to select whether the optimization is Simple (mono-criterion) or Multi-criteria. For Multi-criteria structural optimization choose a solution from the Results which are displayed below in the form after structural optimization. Determine for the follwing simulations whether the results should be Recalculated (relevant only for separate Pre-stage and Main stage).
Set the economic constraints Interest rate and Economic time periods in years (period under consideration, see the following figure). The Period duration is fixed at one year and cannot be changed. Activate the Price change across years. If checked, Inflation rates, Reinvestment costs, and expiring payments (from Electricity Tariff CHP Surcharge) are averaged in the structural optimization, and the costs or revenues are discounted or compounded to the start year. If deactivated, the structural optimization calculates the optimal energy system for the Start year.
Click in the box provided if you Use your own compressed time series. Otherwise, select the level for the Time Series Compression. Note the hints on Time Series Compression in the article about the Process Steps of Structural Optimization.
Other general parameters of the structural optimization are specified in the Simulation ribbon: Set the Gap in % and the time for Termination in seconds for the main stage and, if necessary, for the pre-stage.
Objective Function
Select the objective function via the split button in the Structural optimization group of the Simulation ribbon:
Annualized total cost, 
Investment costs, or 
Net present value.
The following relationship applies between the target function contributions for structural optimization:
\(Net\ Present\ Value = Investment\ Costs + RBF \cdot Operating\ Costs\)
\(Annualized\ Overall\ Cost = Net\ Present\ Value / RBF \)
RBF is the annuity present value factor (German: Rentenbarwertfaktor–cash value factor) that results from the selected Interest rate i for each year (Period duration) and the Economic time periods in years T:
\(RBF(i,T)={\frac {(1+i)^{T}-1}{(1+i)^{T}\cdot i}} \)
For the standard values 4 % interest rate and 10 a period under consideration, the cash value factor is 8.11 a. In general, the factor determines how much higher investment costs are offset by savings in annual operating costs during dimensioning. The savings in operating costs are discounted at the specified interest rate.
Results of Structural Optimization
The Results of the structural optimization are displayed for the individual variables both in the Simulator window from Log level 3 Details (see the following figure) and after the successful simulation in the Simulation form under Settings → Structural optimization in a table (see the figure after next).
To do this, uncheck the box Recalculate results in the form of the Simulation node.
