Photosynthetically active radiation separation model for high-latitude regions in agrivoltaic systems modeling

Authors: MA LU, S. - Collaborator; YANG, D. - Harbin Institute Of Technology (HIT); Anderson, Martha; ZAINALI, S. - Collaborator; STRIDH, B. - Collaborator; AVELIN, A. - Collaborator; CAMPANA, P. - Collaborator

Submitted to: Solar Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2024
Publication Date: 2/15/2024
Citation: Ma Lu, S., Yang, D., Anderson, M.C., Zainali, S., Stridh, B., Avelin, A., Campana, P. 2024. Photosynthetically active radiation separation model for high-latitude regions in agrivoltaic systems modeling. Solar Energy. 16(1). Article e0181311. https://doi.org/10.1063/5.0181311.
DOI: https://doi.org/10.1063/5.0181311

Interpretive Summary: Agrivoltaic systems are a novel concept in sustainable development strategies, combining solar energy harvesting and agricultural activities on the same land area. The agrivoltaic technology is an efficient, effective, and innovative solution to tackling land use competition; however, it is critical that crop yields not be negatively impacted below a tolerable threshold due to shading by the solar modules. Further, the composition of the light in terms of direct and diffuse light fractions is known to impact crop light-use efficiency, with diffuse light able to penetrate deeper into the plant canopy. Shading increases the diffuse light fraction; therefore, knowing the amount of diffuse and direct photosynthetically active radiation (PAR) incident to a specific crop area beneath the agrivoltaic system implies a more accurate crop yield estimation. In this paper, we examine and refine several empirical models for estimating PAR direct and diffuse fractions over three study locations in Sweden, an area of expanding implementation of agrivoltaic networks. The models leverage atmospheric data available from satellites as well as standard meteorological datasets. The best performing model can estimate diffuse PAR with an R2 exceeding 0.91 and errors of less than 17%. This model will provide valuable input to studies assessing the efficacy of new agrivoltaic systems in Sweden, and the associated impacts on crop production.

Technical Abstract: Photosynthetically active radiation (PAR) is a key parameter for modelling the photosynthetic behaviour of plants in response to sunlight and, subsequently, for determining crop yield. Separating PAR into direct and diffuse components is of significance to agrivoltaic systems, which combine solar energy conversion and agricultural farming on the same portion of land. Placing photovoltaic on agricultural land results in varying shading conditions throughout the day and seasons, producing a higher contribution of incident diffuse PAR to the crops beneath the system in these shaded regions. Additionally, photosynthesis is more efficient under conditions of diffuse PAR than direct PAR per unit of total PAR. This work introduces a new separation model for PAR, which is able to accurately estimate diffuse PAR from global values. The model modifies the YANG2 model by adding four new predictors: the optical thickness of PAR, vapour pressure deficit, aerosol optical depth, and albedo of PAR. The proposed model has been calibrated, tested, and validated at three sites in Sweden with latitudes above 58° N, obtaining R2 exceeding 0.91 and nRMSE less than 17%. Compared to YANG2, which was previously found to be a high-performance model, the new model is superior by up to 1% both in R2 and nRMSE. Additionally, an analysis of the seasonal trends and variation of the different PAR components is provided to alleviate the dearth of PAR studies in high-latitude regions.