Exploring the possibility to use energy from solar panels to provide artificial light through LEDs in a vertical hydroponic crop of lettuce

D. Savvas, O. Voutsinos, M. Mastoraki, G. Liakopoulos, K. Dekoulis, G. Ntatsi
One of the biggest challenges of vertical farming is to minimize the energy cost of production while maintaining the quality of the products. In the current study, a hybrid-solar lighting vertical farming system, powered by photovoltaics during the sunny hours, without using any inverters or converters, that automatically switches to the main power grid during dark hours, named PHOTON RACK (PR), constructed jointly from DEKOULIS LAB and the Agricultural University of Athens, was tested. To test the efficiency of the system, butterhead lettuce (Lactuca sativa L. ‘Glory’) was cultivated by applying the following four treatments: A) high light intensity treatment (HLI) in the upper layer of the PR, consisting of 16 hybrid-solar LED tubes which were powered by two 400 W photovoltaic panels providing 310 μmol m‑2 s‑1 irradiance; B) the PR lower layer, the same as above but powered solely by the main electricity grid; C) the PR intermediate layer, low light intensity treatment (LLI), with 8 LED tubes providing 188 μmol m‑2 s‑1 irradiance. All PR layers were operated under a 12 h day‑1 photoperiod; D) hydroponic cultivation in recirculating nutrient solution (NFT) in a glasshouse (GH) with an average of 144 μmol m‑2 s‑1 irradiance and a 10 h day‑1 photoperiod. The upper layer consumed 4.5 times less energy than the lowest layer. The plants exposed to HLI had a standard morphology whereas those exposed to LLI had a strong shade avoidance-like appearance. Root and shoot fresh weight, leaf number and area, chlorophyll level, photochemical yield of photosystem II (ΦPSII), photochemical quenching (qP) and real evapotranspiration (ETR) were significantly higher in the HLI treatment. Leaf nitrates were similar in all PR treatments and significantly lower than in the GH. In conclusion, the HLI hybrid-solar of the PR was capable of minimizing electricity cost while producing safe for consumption lettuce.
Savvas, D., Voutsinos, O., Mastoraki, M., Liakopoulos, G., Dekoulis, K. and Ntatsi, G. (2020). Exploring the possibility to use energy from solar panels to provide artificial light through LEDs in a vertical hydroponic crop of lettuce. Acta Hortic. 1296, 943-950
DOI: 10.17660/ActaHortic.2020.1296.120
https://doi.org/10.17660/ActaHortic.2020.1296.120
artificial lighting, hydroponics, plant factories, soil-less culture, vertical farming
English

Acta Horticulturae