## 3 Levelised Cost of Electricity of CSP Plants Based on sCO\({}_{2}\)
### Overall Analysis of the Levelised Cost of Electricity
* The trend followed by \(LCoE\) is approximately symmetrical to the figures of merit indexing thermal performance (\(CF\) and \(E_{year}\)) and balanced by the financial model. Higher \(CF\) usually comes with lower \(LCoE\) but, if the two options with the lowest \(CF\) are considered--Partial Cooling cycle located in Tonopah for Cases 1 and 2--it is found that Case 1 always yields the highest \(LCoE\) whereas the SunShot model can compensate for the \(CF\) effect in Case 3. * If the same financial model is considered (Cases 1-2, Cases 3-4), the lowest \(LCoE\)s are achieved by plants presenting better performance metrics (higher \(CF\) and \(E_{year}\)), as observed in Figures 7a,b and 8a,b. Based on this foreseeable result, increasing the capacity factor of a plant (and therefore its annual yield) is confirmed to be of capital importance to increase the feasibility of sCO\({}_{2}\)-based CSP plants. Based on the foregoing results, it is difficult to ascertain the best power cycle, given that the three power cycles yield very similar \(LCoE\) in the order of 8.5-9.5 \(\zeta\)/kWh, see Figure 8a,b. Moreover, the small differences observed lie within the cumulative uncertainty incurred by all the assumptions made throughout the analysis. Figure 9 presents the final comparison of \(LCoE\) for the reference plant using the power cycles considered. The length of each bar comes determined by the values taken by \(LCoE\) for the different cases considered in Table 6. The lowest cost of electricity is obtained for the best combination of the Allam cycle (8.33 \(\zeta\)/kWh), while the worst case based on the Partial Cooling cycle yields the highest \(LCoE\) (11.02 \(\zeta\)/kWh). Interestingly, the range of \(LCoE\) for plants based on steam turbine technology falls entirely within the values covered by the other cycles. This confirms the lack of a clear, unambiguous conclusion about the optimum CSP plant concept stemming from this work, as suggested in the introductory section of the paper. To the authors' opinion, however, this result does confirm the large potential of sCO\({}_{2}\) power cycles for CSP applications, which must be considered as a solid alternative to the standard steam Rankine cycle approach in spite of the apparently marginal gain suggested by Figure 9. Such a strong statement is based on the fact that, even if the results obtained are still far from the 6 \(\zeta\)/kWh target set by the SunShot programme (or 3 \(\zeta\)/kWh in the longer term), it must not be forgotten that the \(LCoE\) values presented in this paper for sCO\({}_{2}\) are estimates based on deliberately conservative assumptions. For instance, the utilisation of molten salts that are less costly than FLiNaK, which is a reasonable assumption for an actual power plant in the future, would certainly cut down installation costs and, therefore, \(LCoE\) by a large fraction given the dominant role of the Thermal Energy Storage System in determining the economic performance of the plant. This is a very likely possibility in the near future which would cut LCoE down for the sCO\({}_{2}\) cases in Figure 9 but would not affect the cost of the steam-based case. Therefore, it may as well be the case that mid-term CSP plants employing Allam and Partial Cooling cycles are able to achieve \(LCoE\)s lower than those obtained in this research, and closer to the SunShot objective, once the very strong economies of scale that are characteristic of CSP start impacting sCO\({}_{2}\) power blocks. There is no reason why a cost decline similar to that experienced by conventional CSP-STE plants cannot be experienced by this new technology in the near term. With this in mind, it is concluded that more accurate part-load models and integration schemes in SAM or equivalent software will prove that either the Allam or Partial Cooling cycle layouts have the potential to make a strong case for the next generation of CSP plants based on sCO\({}_{2}\) power cycles,  
Figure 9: Range of Levelised Cost of Energy (\(LCoE\)) for CSP plants based on different power cycles.