Optimal control of plant growth in a plant factory using a plant model *

A plant factory (PF) is an environmentally controlled facility that can maintain stable crop cultivation while ensuring rapid production and good crop quality by controlling temperature, humidity, light and other growing factors. Although it has many advantages, PFs have high initial and operating costs, especially the energy for lightening. In this work, we aim to improve the light use efficiency by optimizing the combination of environmental conditions (case of light intensity and CO2 level) in order to fit the best plant’s demand. To reach this goal, the effect of environmental conditions on daily assimilation rate is simulated using a process-based plant model ‘TomSim’. The daily profit of a PF under different light intensities and CO2 concentrations is evaluated. As a result, the optimal light and CO2 conditions can be obtained for a given leaf area index (LAI) of the lettuce plant. Smaller LAI, which means the early growth stage, requires lower light intensity. A dynamic light control strategy for a PF is expected that can fit plant demand during its growth period while keeping relatively low cost.