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Decomposition models of solar irradiance estimate the magnitude of diffuse horizontal irradiance from global horizontal irradiance. These two radiation components are well known to be essential for predicting the performance of solar photovoltaic systems. In open-field agrivoltaic systems (i.e., the dual use of land for both agricultural activities and solar power conversion), cultivated crops receive unequal amounts of direct, diffuse, and reflected photosynthetically active radiation (PAR). These uneven amounts depend on where the crops are growing due to the non-homogenous shadings caused by the presence of the installed solar panels (above the crops or vertically mounted). It is known that, per unit of total PAR, diffuse PAR is more efficient for canopy photosynthesis than is direct PAR. For this reason, it is essential to estimate the diffuse PAR component when agrivoltaic systems are being assessed, in order to properly predict the crop yield. Since PAR is the electro-magnetic radiation in the 400-700 nm waveband that can be used for photosynthesis by the crops, several stand-alone decomposition models typically used to split global horizontal irradiance are selected in this study to decompose PAR into direct and diffuse. These models are applied and validated in three locations in Sweden (Lanna, Hyltemossa and Norunda) using the coefficients stated on the models' original publications and locally fitted coefficients. The results showed weaker performances in all stand-alone models for non-locally fitted coefficients (nRMSE ranging from 27% to 43%). However, performances improve with re-parameterization, with a highest nRMSE of 35.24% in Lanna. The Y(ANG)2 decomposition model is the best-performing one, with the lowest nRMSE of 23.75% in Norunda when applying re-estimated coefficients. Country level sets of coefficients for the best-performing models (Y(ANG)2 and STARKE) are given after parameterization using combined data for all three locations in Sweden. These Sweden-fitted models are tested and show an nRMSE of 25.08% (Y(ANG)2) and 28.60% (STARKE). These results can be used to perform estimations of the PAR diffuse component in Sweden wherever ground measurements are not available. The overall methodology can be similarly applied to other countries.

Photosynthetically active radiation is a key parameter for determining crop yield. Separating photosynthetically active radiation into direct and diffuse components is significant to agrivoltaic systems. The varying shading conditions caused by the solar panels produce a higher contribution of diffuse irradiance reaching the crops. This study introduces a new separation model capable of accurately estimating the diffuse component from the global photosynthetically active radiation and conveniently retrievable meteorological parameters. The model modifies one of the highest-performing separation models for broadband irradiance, namely, the Yang2 model. Four new predictors are added: atmospheric optical thickness, vapor pressure deficit, aerosol optical depth, and surface albedo. The proposed model has been calibrated, tested, and validated at three sites in Sweden with latitudes above 58 °N, outperforming four other models in all examined locations, with R2 values greater than 0.90. The applicability of the developed model is demonstrated using data retrieved from Sweden's first agrivoltaic system. A variety of data availability cases representative of current and future agrivoltaic systems is tested. If on-site measurements of diffuse photosynthetically active radiation are not available, the model calibrated based on nearby stations can be a suitable first approximation, obtaining an R2 of 0.89. Utilizing predictor values derived from satellite data is an alternative method, but the spatial resolution must be considered cautiously as the R2 dropped to 0.73.

In agrivoltaic systems combining solar photovoltaic and agricultural activities, ground albedo is mainly characterized by the crop and its seasonal variations. This study examines the effects of using fixed, satellite-derived, and hourly measured albedo on the performance of a vertical bifacial system and a 1-axis tracking system using a bifacial photovoltaic model (AgriOptiCE®). The model is developed with Matlab® and partially based on the open-source package pvlib. AgriOptiCE® is firstly validated by comparing estimated front and rear irradiances with on-site measurements for specific periods from a 1-axis tracker site in Golden, USA and a vertical agrivoltaic system in Västerås, Sweden. Furthermore, photovoltaic system power output estimations using AgriOptiCE® are also validated for the vertical agrivoltaic system and the conventional ground-mounted fixed-tilt system at the same location. The validations demonstrate the high accuracy of the proposed model in estimating front and rear irradiances and power output, obtaining R² > 0.85 for all the studied cases. The study results indicate that measured albedo provides the highest accuracy, while satellite- derived albedo has poorer results due to the broader spatial, temporal, and spectral resolution. Fixed albedo is not recommended for yearly assessment of bifacial PV systems because it cannot account for snow events and daily variations, resulting in lower overall accuracy. 

Agrivoltaic systems offer a solution to the debate over using agricultural land for food production or energy conversion. Conventional silicon solar panels often shade plants excessively, impacting growth. Wavelength-selective photovoltaic (WSPV) technologies address this by allowing the transmission of beneficial wavelengths for photosynthesis while converting less useful ones into electricity. Wavelength selectivity can be achieved through various methods, such as by tuning photoactive layers, applying colored semi-transparent layers, utilizing mirrors and lenses, or designing spectrally selective luminophores. While evidence suggests that these technologies effectively share sunlight, many of them are yet to be fully implemented and evaluated. This review covers current WSPV technologies, discussing their classification, status, and future prospects. It also provides appropriate PV performance metrics for WSPV technologies in agricultural applications and advocates for standardized reporting practices in crop experiments conducted under WSPV systems, accompanied by practical suggestions. Solar cell efficiency limits under spectral sharing for crop production and the optimal band gap under varying levels of photosynthetically active radiation for crop growth are further examined as guidance for future development.

While most agrivoltaic systems use opaque silicon photovoltaics, their excessive shading has shifted interest toward semi-transparent wavelength-selective photovoltaic (WSPV) technologies. These technologies aim to transmit light beneficial for crops’ growth while converting unused wavelengths into electricity. This study presents two modeling approaches: one for simulating light transmission through WSPV systems and the other for estimating leaf photosynthetic rates from the wavelengths received at the crop level. Both models incorporate the composition of the light spectrum, an aspect often overlooked in earlier models where broadband light values were sufficient. However, in WSPV systems, consideration of the spectral light distribution is key. The models were validated using experimental data from semi-transparent magenta-colored cadmium telluride (CdTe) WSPV systems, demonstrating satisfactory accuracy (R2 > 0.89). Additionally, the study evaluates two metrics, the yield photon flux (YPF) and effective photosynthetically active radiation (EPAR), to assess the photosynthetic efficiency of WSPV technologies in terms of light quality. A global crop suitability assessment, based on light requirements (light quantity) for different plants, highlights the potential of various WSPV technologies in agrivoltaics and aims to guide their future implementation. For instance, semi-transparent magenta CdTe PV and red-transmittance-dominated organic PV (OPV) modules, with average PAR light transmittance around 20%, appear to provide effective shading in most regions. These systems can support medium-light plants (daily light integral [DLI] >6 mol m−2 day−1) even in higher latitudes during sunnier months. Conversely, blue-dominated OPV and a neutral-colored semi-transparent crystalline silicon PV provide higher transmittance (around 50%), making them suitable for plants with very high light demands (DLI >16 mol m−2 day−1), but the quality of the light transmitted is less efficient or unaltered in terms of photosynthetic performance with respect to sunlight.