Spectral Albedo in Bifacial Photovoltaic Modeling: What can be learned from Onsite Measurements?

Abstract

This contribution reports on a yearlong spectral albedo measurement campaign performed in Roskilde, Denmark. Four albedo scenarios are monitored using three sensor types. The ground surfaces include green grass, dry grass, gravel, and snow all of which have been monitored with albedometers based on spectroradiometers, silicon-pyranometers, and thermopile pyranometers. Implications of using the various albedo data sources/assumptions in bifacial PV modeling are assessed with the spectrally weighted bifacial energy gain (BEG). We find that BEG differs by as much as 3% with the different albedo sensors and BEG can deviate by as much as 7% from the ground truth when an incorrect static spectral albedo assumption is used. Finally, the spectral mismatch factor (SMM) is calculated to summarize rear plane of array (POA) spectral shifts. Our measurements show midday backside POA spectral shifts as high as 25% for Silicon bifacial PV devices mounted on single axis trackers above grass.

Testing New Kinetic Models and Calibration Methods for Rock Surface Luminescence Exposure Dating Using Controlled Experiments

“…(1) Daylight exposure Eight granite and eight sandstone samples were exposed to daylight in Denmark for 1, 2, 21, 31, 68, 118, 566, and 730 days in the period from April 2018 to July 2020 (see Table 2). The solar irradiance spectrum was recorded every 5 min during 2020 using a EKO MS711 spectroradiometer (Riedel-Lyngskaer et al, 2021, see section SI.4).…”

“…The solar spectral irradiance was measured every 5 min from sunrise to sunset throughout 2020 using a EKO MS711 spectroradiometer (Riedel-Lyngskaer et al, 2021). From these measurements we can calculate a daily mean of the solar spectral flux as a function of wavelength (i.e.…”

“…The solar spectral irradiance (J s −1 m −2 nm −1 ) was measured every 5 min from sunrise to sunset at Risø, Denmark throughout 2020 (Riedel-Lyngskaer et al, 2021) and these data can be used to calculate the flux 𝜑(𝜆) and hence the incident number of photons for each daylight exposed sample taking into account the number of daylight hours and the intensity of the flux at individual wavelengths ranging between 300 and 1100 nm. The main effect of seasonal change is in the intensity of the incident daylight as there was no significant change in the shape of the spectrum during the year (see section SI.4.2).…”

Time‐varying, ray tracing irradiance simulation approach for photovoltaic systems in complex scenarios with decoupled geometry, optical properties and illumination conditions

“…Spectrally resolved irradiance simulations are important for bifacial PV systems 37–39 and will be essential in the near future to simulate the yield of tandem PV modules 40,41 . Meanwhile, the ability to simulate time‐varying optical properties can be useful to model the effects of rain and snow on the surface reflectivity 42 and improve the calculation of the bifacial energy gain in large PV power plants 43 . Whereas the implementation of these features in transposition and view factor models is rather simple, adding these simulation capabilities to existing RT implies a heavy computational burden.…”

“…40,41 Meanwhile, the ability to simulate time-varying optical properties can be useful to model the effects of rain and snow on the surface reflectivity 42 and improve the calculation of the bifacial energy gain in large PV power plants. 43 Whereas the implementation of these features in transposition and view factor models is rather simple, adding these simulation capabilities to existing RT implies a heavy computational burden. Considering that daylight coefficients depend on the wavelength-specific optical properties of the surfaces composing the scene, ray tracing simulations should be repeated to calculate daylight coefficients at every wavelength and for every possible combination of optical properties.…”