## 5 Conclusions  
According to the International Standard IEC 62670-3 the data of power performance of CPV devices measured outdoors have to be filtered in order to restrict the set only to those points close to the Concentrator Standard Operating Conditions. The strictest requirement is that all the three Spectral Matching Ratios (SMR) must be in the range 1.00 \(\pm\) 0.03, to eliminate points acquired with spectral conditions too far from the reference spectrum. The present study calculated, using a Monte Carlo method, the uncertainties associated with the three SMR measured using a calibrated spectroradiometer and the measured spectral responses of the triple-junction CPV device. The values of the expanded (k = 2) uncertainties are one order of magnitude less than the limit, with the highest value of \(\pm\)0.42% for SMR\({}_{23}\), and hence the 3% value is meaningful for this measurement method. However, the uncertainties of solar spectrum and spectral response measurements at ESTI are representative of only a few top-class laboratories in the world, and hence typical uncertainties on SMR are expected to be generally higher. It is advisable for each laboratory dealing with outdoor power measurements of CPV devices to declare also the specific uncertainties of the SMR used to filter the acquired data. The uncertainties of SMR calculated using an isotype component cell has not been considered in this study, but the fact that the isotype device sub-junctions are generally different to the particular device under test leads to an approximate method.  
**Acknowledgments:** The present work has been funded by the European Commission Directorate General Joint Research Centre, in the framework of the Horizon 2020 programmes. The European Commission granted also for the Open Access to this paper.  
**Author Contributions:** [PERSON] conceived this work, and for this work he was responsible for the design and implementation of the Monte Carlo analysis and he wrote the paper. [PERSON] is the responsible of metrology laboratory at ESTI, and for this work he contributed with uncertainty analysis of solar spectrum measurements. [PERSON] is responsible of the concentrator photovoltaic activities at ESTI, and manages the outdoor setup measurement system. Authors would like to highlight the contribution of [PERSON] in the review phase of this article.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Abbreviations**  
\(\lambda\) Wavelength \(SMR_{ik}\) Spectral Mismatch Ratios between junctions \(i\) and \(k\) (\(i\), \(k\) = 1... 3, \(i\
eq k\)) \(\Phi_{i}(\lambda)\) Spectral responsivity of \(i\)-th junction \(G(t,\lambda)\) Spectral irradiance measured at time \(t\)\(\hat{G}(\lambda)\) Reference spectral irradiance AM1.5D \(J_{i}(t)\) Short circuit current produced by junction \(i\) (\(i\) = 1... 3) at time t \(\hat{J}_{i}\) Short circuit current produced by junction \(i\) (\(i\) = 1... 3) with reference spectrum \(u(\cdot)\) Standard uncertainty associated to a quantity \((\cdot)\)\(u_{C}(\cdot)\) Combined uncertainty associated to a quantity \((\cdot)\)\(U_{C}(\cdot)\) Expanded uncertainty associated to a quantity \((\cdot)\)\(\mathbb{H}[f(x_{i})]\) Hermite interpolant of the function \(f(x)\) on the nodes \(x_{i}\)