Search

Dirt accumulation ("soiling") on the surface of photovoltaic (PV) modules may cause significant energy output reductions ("soiling losses"). The adoption of suitable soiling mitigation strategies can make PV deployment more attractive, but it requires the assessment of the magnitude and the seasonal evolution of the soiling losses at local scale, as they are highly dependent on the regional climate, the meteorological conditions and the surrounding environment. For the purpose of estimating them for building integrated and building applied PV systems in Madrid city, Spain (i.e. under Mediterranean climate conditions), a systematic optical analysis was performed during a 15-month experimental campaign using a rooftop soiling test bench which allowed the exposure of multiple glass coupons at two tilt angles of interest (8° and 35°) in a semiurban environment. There was no cleaning schedule so that the exposed glass coupons were simply washed away by the rain. Broadband transmittance reductions (T loss) indicated the occurrence of low soiling losses with yearly-averaged T loss values of 1.49% at 8° and 1.04% at 35°. Regarding the soiling evolution, the local precipitation regime played a fundamental role. Soiling losses were negligible during frequent-rainfall periods, experienced a moderate increment in spring (March–April), and increased notably during the dry summer season, reaching annual maxima in July (5.13% at 8° and 3.89% at 35°). In order to minimize the local soiling losses, performing module cleaning operations at least during these two times of the year is encouraged. Concerning the soiling spectral effects, the optical loss increased towards shorter wavelengths, making wide-bandgap PV technologies more sensitive to local soiling. Finally, when applying PV performance prediction models which include soiling, the recommended local values for the daily soiling rate and the rain threshold are 0.11%/day and 5.3 mm at a tilt angle of 8° and 0.09%/day and 3.3 mm at a tilt angle of 35°. • BIPV-/BAPV-oriented soiling experiment. • Soiling test bench for the long-term exposure of glass coupons. • Assessment of the soiling optical losses on a yearly and a seasonal basis. • The annual rainfall regime played a fundamental role on soiling. • Daily soiling rates and rain thresholds estimated for PV yield prediction tools. [ABSTRACT FROM AUTHOR]

Building integrated photovoltaics (BIPV) represents a strategic part of the future building vision with a huge potential driven by the growing shift towards renewable energy resources. However, transforming building surfaces into active electricity generators must consider the thermal behaviour of photovoltaic (PV) panels since it affects both the power conversion efficiency of the PV modules and the thermal comfort of the building. Although several methods have been developed for the evaluation of the thermal performance of the PV modules, at present, no clear consensus exist on which model fits better for this application considering different PV technologies and real operating conditions. This work presents the study of the thermal behaviour of four different PV technologies (polycrystalline silicon, cadmium telluride, amorphous silicon; and organic PV) based on measurements collected by an experimental system located in Murcia (southeast of Spain) during a full year. Two prediction models to estimate the operating cell temperatures of PV modules (NOCT and Sandia) have been evaluated for their suitability in BIPV systems. The results show how both models strongly depend on the incident solar irradiance magnitude and orientation. Furthermore, the correlation between ambient and module temperature difference and the in-plane irradiance shows a thermal hysteresis effect that is mostly independent of the technology but strongly dependent on orientation, with special impact for east and west faces. The results should be taken into consideration for more accurate estimations of electricity production of BIPV systems. [ABSTRACT FROM AUTHOR]

Incident solar radiation modelling has become of vital importance not only in architectural design considerations, but also in the estimation of the energy production of photovoltaic systems. This is particularly true in the case of buildings with integrated photovoltaics (PV) systems having a wide range of orientations and inclinations defined by the skin of the building. Since solar radiation data at the plane of interest is hardly ever available, this study presents the analysis of two of the most representative transposition models used to obtain the in-plane irradiance using as input data the global and diffuse irradiation on the horizontal plane, which can be obtained by satellite-based models or ground measurements. Both transposition models are validated with experimental measurements taken in Murcia (southeast of Spain) and datasets provided by the photovoltaic geographical information system (PVGIS) and the National Renewable Energy Laboratory (NREL) for vertical surfaces facing the four cardinal points. For the validation, the mean bias deviation, root mean square error and forecasted skill were used as indicators. Results show that the error rate decreases slightly for clear days. Better results are also obtained by dismissing data with low solar elevation angles so as to avoid shadowing effects from the surroundings in the early and late hours of the day, which affects mainly the performance of the transposition models for west and east surfaces. The results highlight the potential of equator-facing façades in winter time when the received irradiation can be twice as much as the one collected by the horizontal plane. It is also noteworthy that the operating conditions of all façades are mainly low irradiance and medium temperature at these locations. [ABSTRACT FROM AUTHOR]