An integrated Energy-Yield-Cost model to evaluate clean energy solutions for vertical farms

Abstract

Despite the efficiency of vertical farms in terms of land and water, the main challenge of these systems is energy consumption and the cost of unit production. The aim of this study is to develop an integrated dynamic energy-yield model to determine the interactions between energy and yield and provide a cost-benefit analysis for studying different clean energy solutions. For this aim, firstly, the energy and mass balances in the case of a typical vertical farm container in Tehran, Iran are analyzed considering the plant dynamic growth and evapotranspiration model of lettuce (Lactuca sativa L.). Secondly, a cost model is added to calculate the cost of unit production. Two strategies are examined, including (wasted) CO2 injection and the implementation of the solar photovoltaic system. According to the results, the specific electricity consumption for lettuce production and the cost of unit production in the case study (a typical vertical farm container in Tehran, Iran) are 11.34 kWh/kg and 3.78 $/kg, respectively. Furthermore, the share of the lighting system and dehumidifier system in the total specific electricity consumption for lettuce production is 78 % and 19 %, respectively. Based on the sensitivity analysis, increasing photosynthetic photon flux density without adjusting CO2 concentration causes an increase in the specific electricity consumption and cost of unit production (from 4.03 $/kg at 300 µmol/(m2.s) and 400 ppm to 3.30 $/kg at 500 µmol/(m2.s) and 1000 ppm). In addition, by using wasted CO2, the cost of unit production drops by 22 % compared to the case study. The results of the solution evaluation indicate that for our case study, 4.7 m2 of solar panels are required to supply the electricity demand for each square meter of the vertical farm (2.35 m2 of solar panels are required for each square meter of cultivation area). The developed model in this research provides the possibility of examining the interaction of energy, yield, and cost of unit production with hourly time steps in a vertical farm simultaneously. Also, it can evaluate the different clean energy solutions on the vertical farms’ energy, yield, and cost of unit production.