Reducing the carbon footprint of greenhouse grown crops: re-designing LED-based production systems
To fulfill the market demand for year-round high-quality production, the use of assimilation light has increased over the last decades by 10% per year and continues to expand. The electrical consumption involved largely contributes to the high CO2 emission of greenhouse horticulture. Following the Kyoto protocol, the emission of greenhouse gases should be reduced. Light-emitting diodes (LEDs) can contribute to the reduction in carbon footprint by their high efficiency in converting electricity into light. Due to their low heat emission, LEDs can be positioned within the canopy, which allows the design of new, low-carbon production systems. Inter-canopy LED lighting is already commercially used on a small scale. This paper describes the steps taken to further optimize LED-based production systems. Since it is impossible to test all possible strategies of using LED lighting, a 3D functional-structural plant model was used to do scenario calculations to determine the light interception of the canopy and crop photosynthesis at different positions and orientations of the LEDs. Orienting inter-lighting LEDs 30° downwards positively affected the light interception by the crop, provided that there was sufficient leaf area below the LEDs to prevent light loss to the floor. Replacing the conventional high-pressure sodium (HPS) lamps by LED lamps (efficiency 2.3 µmol J-1) reduced the carbon footprint of a tomato crop by approximately 15%, due to a combination of the higher efficiency of LEDs and an increased use of thermal energy to maintain plant temperatures. These calculations were validated in a greenhouse trial, where the production and energy consumption of a HPS+LED hybrid system was compared to those of a LED top-lighting and LED inter-lighting combination. Plant development and production levels were comparable, whereas the electrical consumption in the LED+LED system was 37% lower than under HPS+LED lighting. Approximately half of the reduction in electricity was used for additional heat input to maintain plant development rate, which agreed well with the carbon footprint calculations. Work in the near future will focus on plant architecture and LEDs with altered light emission patterns, aiming to design new LED-based production systems, which combine a high production level with a low-carbon footprint.
Dieleman, J.A., de Visser, P.H.B. and Vermeulen, P.C.M. (2016). Reducing the carbon footprint of greenhouse grown crops: re-designing LED-based production systems. Acta Hortic. 1134, 395-402
3D functional-structural plant model, tomato, assimilation light, electricity, energy consumption, light use efficiency, HPS