Key performance indicators for PVT Systems

In order to judge the performance of a technology, well-defined Key Performance Indicators (KPI’s) are needed. Such indicators are for instance used to quantitatively compare different components or systems, or, as another example, in order to quantify the impact of optimisation steps on a component or a system. KPI’s can be applied both to measurement data and to data generated by mathematical simulation in the component or system design phase. The aim of this report is to provide precise definitions of useful KPI’s for PVT systems. Where possible, these definitions correspond to those used in the technology fields of solar thermal systems and photovoltaic systems. In particular, the KPI's for the thermal performance of PVT systems are to a considerable extent based on the definitions adopted in IEA SHC Task 44 (Hadorn 2015). The stipulation and use of standardized KPI’s and notations will be essential for the comparability of different research results. The KPI's presented here are mainly intended for assessing the performance of PVT systems in field operation or simulated systems, e.g. in the system design phase. Some of the KPI's assess a particular component of the system and others the whole system. In particular, for a given project or location, the KPI's will be useful to compare system solutions based on PVT with solutions based on other technologies. The intended purpose of the presented KPI's is not, however, the assessment and comparison of PVT collector products in standard laboratory testing conditions. For this topic, the reader is referred to Subtask B report B1 "Status Quo of PVT Characterization". The used nomenclature and the KPI definitions are provided in section 2. This is followed by two application examples for the KPI's. The first example, presented in section 3, is the comparison of measurement data of three equivalent buildings that are equipped with three different solar energy systems. In the second example, section 4, KPI's are applied to simulation results, in order to compare the performance of the combinations PV & covered PVT and PV & thermal collectors for the case of a multi-family building. In the separate report D2 "Performance Assessment of PVT Example Systems" a selection of the KPI's defined here is applied to a series of PVT systems in operation