Calibration and Simulation Analysis of Light, Temperature, and Humidity Environmental Parameters of Sawtooth Photovoltaic Greenhouses in Tropical Areas

To investigate the light and temperature environmental parameters of photovoltaic greenhouses in tropical areas, this study adopted experimental measurement and simulation methods to test and simulate the photosynthetically active radiation (PAR), relative temperature and humidity, and other environmental parameters inside and outside two types of serrated photovoltaic greenhouses in Langheng Village, Yangpu, Hainan. The study aimed to explore the distribution laws of PAR, light transmission rates, and relative humidity and temperature inside and outside double-slope and single-slope photovoltaic greenhouses. The ridges of both types of greenhouses run east to west, with photovoltaic panels arranged on the south-facing slopes, covering 57% of the area. The results show the following: (1) The trends of PAR inside and outside both types of photovoltaic greenhouses were consistent across all seasons, with the annual average values were 164.98 μmol/(m2·s) for double-slope and 127.59 μmol/(m2·s) for single-slope; (2) The annual average light transmission rates were 23.91% for double-slope and 19.17% for single-slope; (3) The average indoor temperatures in both types of greenhouses were higher than outside in all seasons, with a temperature difference ranging between 1 and 3 °C; (4) The indoor relative humidity in both types of greenhouses was higher than outside, with the difference reaching up to 6% during summer and autumn; (5) The annual light transmission rates for both types of greenhouses were simulated using Design Builder. The simulation results were generally consistent with the measured values, with the simulated values being higher overall than the measured ones by an average difference within 5%. In summary, the average light transmission rate of the double-slope photovoltaic greenhouse was 4.74% higher that of the single-slope photovoltaic greenhouse and the PAR was 37.39 μmol/(m2·s) higher than the single-slope. Additionally, the average temperature in the double-slope greenhouse was slightly higher and the relative humidity was slightly lower than that in the single-slope greenhouse. Both types of greenhouses could meet the light, temperature, and humidity requirements for cultivating leafy vegetables in tropical areas. Except for the temperature parameters in summer, the performance of the double-slope photovoltaic greenhouse was also better. The Design Builder simulation results showed little difference to the actual measurements and their trends were also consistent. The light transmission rate of photovoltaic greenhouses can be simulated by setting the overall light transmission coefficient of the light-transmitting roofing materials.