Simulation of light environment in a serrated photovoltaic greenhouse and optimization of daylighting roofs based on Design Builder

In the tropical regions represented by Hainan, there are abundant solar and thermal resources, and it is relatively suitable for the construction of photovoltaic greenhouse(PVG). However, the construction of PVG still relies mainly on experience and is incapable of quantifying the balance between the photovoltaic(PV) generation and the light requirements for agricultural production. As a result, actual PVGs are primarily PV-based, without carefully considering the needs of agricultural daylighting. To quantify the influence of the design parameters of PVGs and the layout of PV panels on the internal daylighting of serrated PVGs, and to optimize the daylighting design of the roof, this paper utilizes the Design Builder software to establish gradient models for a multi-span serrated-type PVG in tropical regions. Gradient models were established in terms of aspects, namely span, width of longitudinal/transverse daylighting strip, height, roof angle, and photovoltaic panel coverage rate (P_CR). Daylighting in the greenhouse of each gradient model was simulated, and with the annual average daily light integral(A_DLI) and distribution uniformity (D_U) as evaluation indicators, the influence of various design parameters on the daylighting inside the greenhouse was quantified. The result reveals that: (1) P_CR is the decisive indicator for daylighting in the PVG, and a function between P_CR and the A_DLI is derived as A_DLI =-15.5 P_CR +16.841; (2) Increasing the width of longitudinal daylighting strip significantly improves the A_DLI and enhances D_U while increasing the span has a noticeable effect on improving A_DLI but does not significantly enhance D_U; (3) Increasing the eave height without changing P_CR does not enhance A_DLI but effectively improves D_U; increasing the transverse daylighting strip and adjusting the roof angle hardly improves A_DLI. In summary, it is recommended that the optimal span for PVGs in tropical regions be set within the range of 6.5-8.0m, and the eave height be set within the range of 2.5-3.5m. Preferably, the longitudinal daylighting strip with a width ranging from 0.5-0.8m should be installed. Based on the above relationship function, the P_CR can be calculated according to the appropriate light demand for the cultivated crops. The daylighting design theory proposed in this paper can provide a theoretical basis and reference for the healthy development of the PV industry in tropical regions.