• Design of a Modified Shipping Container as Modular Unit for the Minimally Structured & Modular Vertical Farm

      Cuello, Joel; Liu, Xiang; Slack, Donald; Kacira, Murat; Cuello, Joel (The University of Arizona., 2014)
      The specific aim of this study was to advance the development of the Minimally Structured & Modular Vertical Farm (MSM-VF), an original concept developed at The University of Arizona, by designing a specific modular unit made of a transparent-walled modified standard shipping container for use in climate locations represented by Los Angeles and New York City. The conclusions of the study included: (1) A workable range of temperatures (15 to 30°C) for cultivating tomato in Los Angeles and New York City could be achieved in a transparent-walled MSM-VF shipping-container modular unit by using a cover material of low density polyethylene (LDPE) and a heating, ventilating and air conditioning (HVAC) system with an airspeed of 2 m/s, inlet angle at 60° and outlet position located at the top of the back wall; (2) A workable range of temperatures (15 to 27°C) for cultivating lettuce in Los Angeles and New York City could be achieved by using a cover material of LDPE and an HVAC system with an air speed of 4m/s, inlet angle at 60° and outlet position located at the bottom of the back wall; (3) The annual energy demands of the plastic-walled MSM-VF shipping-container modular unit were far less than those for the opaque-walled control plant-factory unit in all cases, except in the one case of growing tomato in New York City. Still, in this one exception, the annual energy demand of growing tomato in New York City in the plastic-walled MSM-VF shipping-container modular unit of 557.65 kWh/m² (versus 325.34 kWh/m² for the opaque-walled control plant-factory unit) was significantly lower than that of 711.91 kWh/m², which was the average for 164 greenhouses occupying a total of 16444 m² operated by the Cornell University Agricultural Experiment Station (CUAES) in the state of New York (CUAES Greenhouses); and, (4) The annual energy demands of the plastic-walled MSM-VF shipping-container modular unit were either significantly lower or for one case approximately the same (773.84 kWh/m²) as that of the 711.91 kWh/m² for the New York greenhouses. By contrast, the annual energy demands of the opaque-walled control plant-factory unit significantly exceeded that of the 711.91 kWh/m² for the New York greenhouses by 170% for Los Angeles and by 126% for New York City, both for growing lettuce. The foregoing results provided significant and reasonable basis for the practicability of Minimally Structured & Modular Vertical Farms made of plastic-walled shipping-container modular units in Los Angeles and New York City as well as in many other mega-cities around the world with similar climates.
    • Modeling and Optimization of Crop Production and Energy Generation for Economic Profit in an Organic Photovoltaics Integrated Greenhouse

      Kacira, Murat; Okada, Kensaku; An, Lingling; Son, Young-Jun (The University of Arizona., 2018)
      This study aimed to achieve the following two goals; first, developing an inclusive model which simulates solar irradiance to a tilted surface, electric energy generated by organic photovoltaic (OPV) modules on tilted greenhouse roof, light transmittance through multi-span greenhouse roof, solar irradiance available at the crop canopy level in the greenhouse, the crop (lettuce in this study) growth and yield, the energy consumed by greenhouse system for cooling and heating, cost and sales of electric energy and the crop. Finally, the model also determined the total economic profit achieved by the optimization program which computed the coverage ratio of OPV module, the period of shading curtain deployment for crop cultivation before and after summer period during which no crop cultivation occurred. The developed model also enables these analyses by adjusting the property of modeled PV modules, thus making it possible to study both organic (typically semi-transparent and flexible) and inorganic (opaque and solid) PV modules. To optimize the economic profit under the assumed environmental and economic conditions, MIDACO solver (http://www.midaco-solver.com/) was adopted. It can solve mixed integer non-linear programming (MINLP) problem by combining an extended evolutionary Ant Colony Optimization (ACO) algorithm with the Oracle Penalty Method for constrained handling (MIDACO-SOLVER, 2018, http://www.midaco-solver.com/index.php/download). All the simulation and optimization source code were written in Python 2.7. The optimization algorithm was licensed by MIDACO solver. The simulator can serve as a building block for further research about Agrivoltaics with new materials including OPV, and can be further enhanced with additional sub-simulation algorithms by other programmers and researchers interested in this field. The optimization results showed that, in Tucson, a semi-arid climate condition, the overall profitability could be increased by extending the cultivation of the lettuce into the summer, using both the shading curtain and OPV modules while decreasing high solar irradiance transmitted into the greenhouse and air temperature inside. The optimized OPV module coverage ratio was 58.0% when assuming its depreciation was completed, cell efficiency was 4.3%, visible light transmittance was 30%, the overall temperature coefficient was 0.02%, and the selling price of generated electricity was same as the purchase price, which was around 0.11 to 0.12 USD/kWh in Arizona. This indicated that the profit of lettuce cultivated in summer exceeded the cultivation cost in summer (labor cost and cooling cost) with a combination of PV module and shading curtain with a simple strategy that changes its deployment time each month according to the monthly average DLI: Thus, high-tech equipment for curtain control may not be required. At the optimal 58.0% OPV deployment rate, the amount of electricity generated per unit area basis was 47.7 kWh/m2 (satisfying 45.7% of the electricity consumption by greenhouse cooling, which was assumed to be the only factor consuming electricity) and the lettuce crop yield was 57.9 kg/m2, with an economic profit generated at 460.5 USD/m2. The simulation code developed also allows user or grower to evaluate alternative OPV coverage ratios and shade curtain deployments providing results on potential electricity generation, crop yields and economic profits. Although the profit made by electricity production with the current OPV film was much less than that of lettuce production, and further analyses should be conducted replacing various assumed values with available real data. The simulation result suggested some shading curtain and lettuce cultivation strategies in arid and semi-arid regions which had a potential to improve the profitability when OPVs integrated with a greenhouse system.
    • Optimizing Carbon Dioxide Concentration and Daily Light Integral Combination in a Multi-Level Electrically Lighted Lettuce Production System

      Kacira, Murat; Caplan, Brian Akira; Giacomelli, Gene; Cuello, Joel (The University of Arizona., 2018)
      There are many issues that will make producing sufficient food for the growing global population a difficult task. Controlled Environment Agriculture (CEA), integrating environmental control and hydroponic technology, can efficiently produce more food with less inputs. The new production practices of vertical farms have precision environmental control and subsequently more consistent and higher productivity with the advantage of being located almost anywhere, especially closer to population centers. A vertical Farm can be described as a fully indoor production system that uses electrical lamps for photosynthetic lighting and high density crops grown in multiple layers. CEA technology of supplementing atmospheric carbon dioxide (CO2) in greenhouse applications to compensate for low light levels, maintain plant photosynthesis, and enhance profits is practiced. However, due to the amount of ventilation generally required in greenhouse environments, maintaining CO2 concentrations can be expensive and impractical. The closed configuration of vertical farms can enhance CO2 use efficiency, however, the use of electrical lighting results in a large electrical power requirement. The goal of this study was to evaluate the level of daily light integrals (DLI) and atmospheric CO2 concentrations that would provide savings of electrical power usage and CO2 supplementation while producing a marketable head lettuce (Butterhead, cv. Fairly) product. Experiments were conducted in a 45 m2 environmentally controlled (air temperature, PPF, DLI, CO2, DO, EC and pH) vertical farm research facility with six values of DLI (9, 11, 13, 15, 17, 19 mol m-2 d-1) and six CO2 concentrations (400, 550, 700, 850, 1000, 1300 ppm), which were maintained constant from transplant through harvest. Plant shoot fresh and dry weights were measured at harvest and compared with resource use accounting of electrical energy for LED lighting, heat pumps for air conditioning, water pumps for nutrient solution circulation, and air pump to maintain dissolved oxygen in the nutrient solution for the roots. It was demonstrated that 1) a linear relationship of increase biomass to increase of DLI existed for all treatments; 2) plants within the 850 ppm CO2 concentration yielded the largest average fresh and dry shoot weights and yields decreased as CO2 was further elevated; 3) the physiological disorder tip burn was more pervasive and appeared sooner for either larger CO2 concentrations and larger DLIs. No tip burn was observed at 400 and 550 ppm CO2 concentrations within any DLI; 4) lettuce grown in lower light intensities had larger physical size dimensions, but were less dense and had less biomass, compared to lettuce grown in higher light intensities which had a smaller physical dimension, but were more dense and thus greater biomass; 5) the metrics for the average overall resource use efficiencies of plant production for fresh weight edible biomass were 69 gfresh kWh-1, 147 gfresh LCO2-1, 20.7 LH2O kgfresh-1 y-1 , and 86.0 kgfresh m-2 y-1; 6) the potential electrical savings from changing the DLI (mol m-2 d-1)/CO2 (ppm) combination from 17/400 to 13/850 in the small scale research facility, to which this study was conducted, is $59 per harvest and $762 for the year (14.4% savings). Larger commercial vertical farm operations lowering the DLI and increasing CO2 concentrations could have a much greater electrical savings potential.