## 3 Levelised Cost of Electricity of CSP Plants Based on sCO\({}_{2}\)  
### Preliminary Notes on the Assessment of the Levelised Cost of Electricity (LCoE)  
In addition to the installation costs presented in earlier sections of this paper, estimating the Levelised Cost of Electricity of CSP plants based on sCO\({}_{2}\) technology requires a model to simulate the off-design performance of the power plant throughout the year. This provides the hourly output of the power plant for the specific boundary conditions--ambient temperature and pressure, available solar radiation, as described in [27] and, more recently [11]. The resulting information is then combined with the installation costs to obtain _LCoE_, as discussed in detail by [PERSON] [13]. To this end, the authors have relied on the System Advisor Model SAM developed by the National Renewable Energy Laboratory of the United States' Department of Energy, since this is widely accepted by the scientific community and already employed in cost estimation for sCO\({}_{2}\) power plants [28, 29]. The first part of this section describes the methodology used to incorporate the part-load performance of the Allam and Partial Cooling cycles into SAM's calculation procedure. Then, this information is used to model the reference 50 MW CSP plant in Table 2, considering either of the cycles selected in the previous section. For each one, two different locations and four different combinations of financial parameters and dispatch control models are assessed. Finally, the results obtained are compared against a state-of-the-art CSP plant using a standard power block based on steam turbines. The input parameters defining the solar field are set to their default values, meaning that the geometry of the field is optimised according to state-of-the-art specifications that are representative of the current industrial practice. The type and composition of the molten salt (or Heat Transfer Fluid considered) is selected in the _Tower and Receiver_ menu, where either commercial solar salts (NaNO\({}_{3}\)KNO\({}_{3}\)) or FLiNaK can be selected. The latter is the same molten salt employed by the in-house models developed by the authors and it is therefore selected for this _LCoE_ assessment. For the power block, SAM is limited to the _Recompression_ layout when it comes to power blocks based on supercritical CO\({}_{2}\) systems, which is a strong limitation in this work. This is why the user-defined option is selected, which enables implementing the off-design performance of the Allam and Partial Cooling cycles modelled with the proprietary code developed by the authors and described in [11]. This is the step where the integration between SAM and the authors' in-house codes actually takes place, enabling a much more detailed and flexible assessment of supercritical CO\({}_{2}\) cycles than otherwise enabled by SAM. This integration requires the following specific information, in addition to more general technical features like the type of cooling system used (air or water cooled):  
* MOD1-Performance as a function of HTF temperature: the part-load performance of the power cycle for variable molten salt (hot) temperature is obtained for three normalised mass flow rates of molten salts, in this case: 0.2, 1 and 1.05. The rated hot temperature of molten salts is set to 770 \({}^{\circ}\)C and this parameter is varied between 700 and 800 \({}^{\circ}\)C in the analysis. * MOD2-Performance as a function of HTF mass flow rate: the part-load performance of the power cycles for variable mass flow rate of molten salts is obtained for three values of ambient temperature, in this case: 5, 15 and 40 \({}^{\circ}\)C. To this end, the same range of normalised mass flow rate as in the previous bullet point is considered; i.e., between 20% and 105% of the rated mass flow rate of FLiNaK.