## Introduction

With TOP-Energy you can determine the optimal plant size for a new plant according to various criteria. Two different methods are available, depending on which energy system is involved and for how many plants the optimum size is to be determined.

## Determining the Plant Size Using Sensitivity Analysis

The simplest way to optimize the plant size is to use the ** eSensitivity Sensitivity Analysis** module.

*Sensitivity Analysis*can be used to vary the nominal power of a plant or the capacity of a storage tank. A

**simulation**with an

**Evaluation of Economical Efficiency**is then carried out for each value of the

**. As**

*Variable Parameter***, you can select the target variables (primitives, e.g.,**

*Sensitive Variables**Dynamic Payback Period*,

*Overall Primary Energy*,

*Internal Rate of Return*).

The result is the size of the plant depending on the *Variable Parameter*. If this function has a minimum or a maximum, the optimum plant size is at this point.

The tutorial **Structural Optimization of Combined Heat, Power, and Cooling** shows the process. For example, the size of the CHP is optimized there. For this purpose, the *Nominal Electrical Capacity* is selected as a variable parameter. A simulation, a variant evaluation, and a variant comparison are carried out for each size. The ** Net Present Value** and the

**of the investment in the CHP are then evaluated. The input data are shown in the following figures.**

*Dynamic Payback Period*As a result, a diagram shows the *Net Present Value* as a function of performance. The *Net Present Value* reaches its maximum at 59 kW. Accordingly, a plant size of 59 kW is the best choice in relation to the *Net Present Value*.

## Discrete Plant Sizes in Sensitivity Analysis

If the plant size in the analysis is to assume discrete values, you can specify discrete values in the *Sensitivity Analysis*. Instead of scanning the solution space linearly, the values from the table are then used and evaluated. The selection is shown in the following screenshot.

## Varying Nominal Power and Investment Costs

In the course of the variation of the leading *Variable Parameter* (e.g., electrical *Nominal Power*), other parameters can also be varied in parallel. This is useful, for example, if the efficiency depends on the nominal power of the system. If, for example, the electrical efficiency increases with the size of the CHP, the *Nominal Electrical Efficiency* and the *Fuel Demand at Nominal Operation* (see the input data of the component) can be selected as second and third parameters in ** eSensitivity. **Then the

*First*

*value*and the

*Last value*belonging to the respective nominal power can be entered. The selection is shown in the following screenshot.

## Determination of Plant Size by Structural Optimization

The optimal size of the plant can be found with the help of *Structural Optimization* as an alternative to *Sensitivity Analysi*s. *Structural Optimization* is particularly useful when several systems need to be optimized simultaneously. This is not possible with a sensitivity analysis because it can only vary one parameter (and, as described above, directly proportional parameters).

For *Structural Optimization*, there is a separate set of components for which the nominal power is not specified, but rather optimized. *Structural Optimization* is described in detail in the article **How Structural Optimization Works**.

The process is also described in the tutorial **Structural Optimization of Combined Heat, Power, and Cooling**. In this tutorial, the optimum plant sizes for an *Absorption Refrigerating System* and a *CHP* unit are sought. The component templates *Absorption_Refrigerating_System_Opt* and *CHP_Opt* from the subfolders ** Structural Optimization** are used for this purpose. In these cases, the nominal power is not specified but determined by optimization.

A disadvantage of S*tructural Optimization* is the somewhat more difficult parameterization of the partial load behavior because this can only be specified via relative and not via absolute partial loads. Furthermore, the *Electricity Tariff CHP Surcharge* is not available for *Structural Optimization*, as it depends on the size of the plant.