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Review

Energy Efficiency of Glasshouses and Plant Factories for Sustainable Urban Farming in the Desert Southwest of the United States of America

by
Md Obyedul Kalam Azad
1,
Nazim S. Gruda
2 and
Most Tahera Naznin
1,*
1
Department of Agriculture, Veterinary and Rangeland Science, University of Nevada, Reno, UNR Extension, 2280 North McDaniel St, Las Vegas, NV 89030, USA
2
Department of Horticultural Sciences, Institute of Crop Science and Resource Conservation, University of Bonn, 53113 Bonn, Germany
*
Author to whom correspondence should be addressed.
Horticulturae 2024, 10(10), 1055; https://doi.org/10.3390/horticulturae10101055
Submission received: 24 August 2024 / Revised: 18 September 2024 / Accepted: 24 September 2024 / Published: 3 October 2024
(This article belongs to the Special Issue Indoor Farming and Artificial Cultivation)
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Abstract

:
The extreme heat and water scarcity of the desert southwest in the United States of America present significant challenges for growing food crops. However, controlled-environment agriculture offers a promising solution for plant production in these harsh conditions. Glasshouses and plant factories represent advanced but energy-intensive production methods among controlled-environment agriculture techniques. This review aims to comprehensively assess how controlled-environment agriculture can thrive and be sustained in the desert southwest by evaluating the energy efficiency of controlled glasshouses and building-integrated plant factories. The analysis focuses on the efficiency of these systems’ energy and water consumption, mainly using artificial lighting, heating, cooling, ventilation, and water management through various hydroponic techniques. Approximately 50% of operational energy costs in controlled glasshouses are dedicated to cooling, whereas 25–30% of energy expenses in building-integrated plant factories are allocated to artificial lighting. Building-integrated plant factories with aeroponic systems have demonstrated superior water use and energy efficiency compared to controlled glasshouses in desert environments. Integrating photovoltaic solar energy and glass rooftops in building-integrated plant factories can significantly reduce energy costs for urban farming in the desert southwest.

1. Introduction

Most deserts are located between the 30th parallel north and the 30th parallel south, where heated equatorial air begins to descend [1]. The southwest regions of the United States of America (USA) fall in the 37th parallel north, including Arizona, New Mexico, Texas, Nevada, and parts of California (Figure 1). Typically, the 37th parallel north is characterized by moderate temperatures and sufficient solar radiation year-round, which is favorable for growing high-yielding fruits and vegetables [2]. However, the southwest of the USA is uniquely characterized as a desert belonging to the Mojave and Sonoran [3].
Due to a quasi-permanent subtropical high-pressure ridge, the southwest has low annual precipitation, clear skies, and a year-round warm climate. The southwest has an arid to semi-arid climate with high summer temperatures, very low annual precipitation, frequent droughts, and significant water scarcity challenges [5,6]. Intense heat increases water evaporation and demands more cooling and irrigation, while dwindling water sources like the Colorado River and groundwater struggle to meet the needs of urban and agricultural use in these regions. Prolonged droughts and excessive water use further strain resources, water conservation, and sustainable practices for the region’s agricultural future [7,8]. Immediate and concerted action is urgently needed to address these challenges. Climate models predict that the 21st century will experience increasing aridity and more severe prolonged droughts in the southwest [9] (Figure 2). The increasing temperature and reduced precipitation in these regions can pose significant challenges to food security and socioeconomic and environmental sustainability [10].
The southwest is expected to grow, reaching over 67 million people by 2030. Suburban populations in the southwest have surged, constituting 50–70% of the total by 2050, and these developments use 70% or more of their water for landscaping, increasing overall water demand [12]. Since 2020, extreme drought has significantly limited irrigation water availability, with Lake Mead at its lowest historical level. Future projections predict higher temperatures, reduced precipitation, and more severe droughts for these regions. Controlled-environment agriculture (CEA) is expanding quickly in the southwestern USA, fueled by the region’s harsh climate and growing demand for sustainable farming solutions. The biggest challenge is high energy demand, especially for cooling and ventilation, due to extreme heat. Many CEA facilities rely on efficient HVAC systems and heat-reflective materials to manage this. There is also a strong move toward renewable energy, particularly solar power, to cut costs and reduce carbon emissions. Innovations like LED lighting, energy-efficient fans, and geothermal systems further improve energy efficiency, with a strong focus on sustainability and resource conservation. This study examines the energy efficiency of glasshouses and plant factory systems, addressing the gap in comprehensive comparisons between them. It provides an overview of current controlled-environment agriculture (CEA) practices and explores energy-efficiency strategies that could enhance the sustainability and profitability of urban farming. Researchers, farmers, and policymakers can use this review to better understand and optimize energy consumption based on local climate conditions through thoughtful facility design and climate control strategies in the desert southwest of the USA.

2. Urban Agriculture/Farming

Urban farming is an option to increase agricultural production to mitigate the challenges of food and nutrition security, water scarcity, climate change, and urbanization [13]. Urban farming systems can enhance water use efficiency and optimize food production using resource-efficient CEA, such as glasshouse (greenhouse) and plant factory production [14,15]. Additionally, urban farming promotes economic growth, technological innovation, and community resilience, which are crucial for the cities’ sustainable future [16]. For instance, Nevada imports $93.8 million in vegetables and melons and $195 million in fruits yearly [17]. However, if five percent of these vegetable and melon imports were replaced by local production, it could create a $4.69 million industry [18]. Urban farms can help address food deserts, areas of a city where residents do not have access to healthy and affordable food [19]. The modern technology-equipped food production system suggested increasing urban resiliency by ensuring the nutrient demand of the urban residents [20]. Semi-controlled and fully controlled year-round greenhouse production, such as screen houses, greenhouses, and plant factories, maximize space, conserve resources, and promote sustainability [21]. Screen constructions use permeable, porous screens for passive climate control that reduce sunlight and wind depending on the natural environment. Greenhouses are covered with impermeable materials like plastic films or glass, allowing for active climate control, either semi- or fully controlled [22].
The production can be at least 10 to 20 times higher when plant food is grown in a CEA compared to an open field [23,24]. For instance, strawberries are produced at 0.5 kg m−2/annum in open fields, whereas in controlled environment greenhouses, it is 7.3 kg m−2/annum. Considering energy consumption, one kg of strawberries needs around 0.20 kWh of energy when grown in a controlled-environment, whereas open-field cultivation needs 0.26 kWh kg−1 [25]. In the open field, tomato production is 7.5 kg m−2/annum; in a controlled greenhouse, the production is 68 kg m−2/annum [26]. This increased yield is achieved due to energy-intensive climate control systems. In the desert southwest, 15% of the land is used for agricultural purposes. Of that, 38% consist of glass or poly greenhouses, 21% are indoor vertical farms, 17% are low-tech plastic houses, and 17% are container farms [27].
The CEA approach addresses the food demands of large populations and aligns with global climate goals by reducing the need for long-distance transportation and mitigating land-use pressures [28]. Glasshouses and plant factories as subsets of CEA are modern production methods that rely heavily on energy for heating, cooling, humidity control, artificial lighting, and irrigation systems [29].
Currently, CEA production makes up 70% of the market share and requires a significant percentage of energy demand. Plant factories are controlled buildings with integrated structures designed with vertically stacked layers where plants are grown under artificial lighting, with regulated temperature, humidity, CO2, and nutrients [30,31]. Plant factories are increasingly recognized for their potential to enhance food security, support local economies, and promote sustainability [32]. Moreover, growing crops in CEA (glasshouses and plant factories) has demonstrated feasibility across various applications [33,34]. However, the energy-intensive nature of CEA, including high start-up costs, limited crop variety, and the need for precise environmental controls, present significant bottlenecks [35] (Table 1).
The balance between the costs of heating and cooling and the benefits of solar radiation in CEA production is significantly influenced by the latitude and external climate of the location [36]. Energy demand, particularly for electricity, is projected to increase, and it is currently sourced from fossil fuels due to the slow transition to renewable energy [37]. Therefore, it is recommended that the production system be operated as energy efficiently as possible and the most suitable system for the local climate be selected [38,39].
The fundamental strategy for CEA’s sustainability is the cost of high energy consumption. It has been reported that as many as 49% of controlled-environment farms in the US were not profitable in 2017 [27]. This is likely because many of these businesses are paying off the substantial initial capital investments required to establish urban farms. High energy consumption poses a significant challenge to the environmental sustainability of glasshouses and plant factories.
The glasshouse and plant factory are advanced systems that have offered a new way of food production, even when more insight is still needed into their energy and resource-use efficiency. The resource-use efficiency of these two systems depends on the outdoor climate, structure properties, operating conditions, product types, geographical location, and latitude [40]. Graamans et al. [39] extensively studied energy efficiency in glasshouse and plant factories in different parts of the world. They reported that plant factories have higher energy efficiency (1411 MJ kg−1) than glasshouses (1699 MJ kg−1). The calculated energy load was 7000 MJ m−2 in the plant factory and 13,000 MJ m−2 for glasshouse lettuce production. The energy needed to produce dry matter in a plant factory is less than that required in a glasshouse in the United Arab Emirates. In cold regions (upper latitude), at least 50% goes to heating, ventilation, and air conditioning (HVAC) [38], whereas 28% of electricity goes to HVAC in plant factory production [41,42]. Nevertheless, plant factories demonstrated more efficiency than glasshouse production regarding overall energy consumption/kilogram of dry-weight lettuce [39]. A promising solution to the food issue is the plant factory, which is especially useful in urban areas and desert regions and has plenty of resources. In contrast to glasshouses, plant factory systems have significantly increased energy use [43]. Plant factories consume more energy than a greenhouse, primarily due to their use of artificial lights and HVAC systems. Graamans et al. [39] have found that a plant factory is more energy efficient than a greenhouse. In contrast, Harbick et al. [44] found that the energy use efficiency of plant factories is inferior to all greenhouse systems. Studies show varying factors of glasshouses and plant factories’ energy consumption and suggested potential strategies to reduce energy consumption (Table 2).

3. Artificial Lighting

The CEA provides many benefits, including year-round plant food production, high productivity, less water use, and minimum environmental impact. A plant factory creates a unique environment for the plant in an artificial environment [39,45]. However, the high purchase costs for artificial lighting in plant factories limit the benefits of plant production. The documented quantities of electrical energy generally required for horticultural lighting in plant factories vary between locations, ranging from 30–52% in lower latitudes [59] to 80% in higher latitudes [60] of the total energy. For example, to produce a single head of lettuce, the electrical energy required is approximately 1.0–1.6 kWh. However, plant factories require more purchased energy (247 kWh/kg dried lettuce) than glasshouse production (182 kWh/kg dried lettuce). Zhang and Kacira [40] studied extensive research on energy consumption, and it is reported that more electricity is required for artificial lighting than the cooling system in plant factories in Riyadh, Abu Dhabi, and Phoenix. According to Kozai and Niu [31], 53% of plant factory energy is consumed by artificial lights, 34% by HVAC systems, and 13% by other sources. According to Ohyama et al. [61], energy consumption for HVAC systems accounts for 16% of energy consumption; lighting accounts for 80%, and other uses for 4%. Shaari et al. [62] reported that 54% of energy is used for HVAC systems, 36% for lighting, and 10% for other purposes. The operation strategy, building design, and various local climates may cause variations in these outcomes.
Studies show that light-emitting diode (LED) technology has significantly enhanced horticultural lighting efficiency. Photosynthetically active radiation efficacies range from 1.3 to 2.1 µmol J−1, with some manufacturers achieving up to 4.0 µmol J−1 [63]. Recent advancements in LED technology enable precise targeting of plant leaves, thereby improving energy efficiency. Additionally, upward lighting systems have been developed to better illuminate outer leaves, delay leaf aging, and reduce waste [64,65,66]. Photosynthetic photon flux’s efficacy could be enhanced using a dedicated light lens integrated with a target light beam [67]. The more efficient the horticultural lighting system, the larger the ratio between the photon flux reaching the plant leaves. So, system effectiveness in horticultural lighting depends on the emission properties of the light sources and the exact distance between the plant leaves and the luminaire. Recent research demonstrated a novel targeted lighting strategy that enables the luminaires to adjust their light distribution dynamically to match adequate crop size at each stage of plant growth [68]. In addition, Graamans et al. [39] suggested an energy-efficient plant factory design called ‘façade design,’ which follows functions, façade construction, and local climate. The authors proved that their façade design reduces cooling, energy, and electricity demand by 18.8%, 6.1%, and 9.4%, respectively. However, as there is abundant sunlight in desert regions, the architectural design of the plant factory should be integrated in a way that makes use of natural sunlight along with supplemental artificial LED light.

4. Water Use Efficiency

CEA in the urban desert is becoming a widespread plant production practice as a local food supplier. In the USA, the plant food production system uses 70% of the country’s freshwater and 17% of fossil fuel and contributes 80% to pesticidal water contamination [69,70,71]. Generally, aeroponics, deep water, NFT, ebb and flow, and aquaponics are used as plant irrigation in CEA farming [72,73,74,75]. Closing the nutrient cycle in hydroponic systems maintains the utility and value of scarce resources [76] and regenerates the environment [77]. Carotti et al. [54] explored how hydroponic systems can recirculate nutrient-rich leachates into a crop’s irrigation system via a closed-loop irrigation system (CLIS). CLIS involves recycling and reusing irrigated water, showing better water use efficiency, reduced nutrient loss, and reduced water pollution through fertigation effluents [78,79,80]. Lettuce production in plant factories can achieve 80 g FW L−1 water, which is significantly higher than that obtained in glasshouses (up to 60 g FW L−1 water) and open fields (up to 20 g FW L−1 water) for the same crop [81]. Controlled-environment systems have a more negligible environmental impact than open-field crops due to higher production efficiency and lower resource usage. Greenhouses significantly reduce water consumption compared to open fields due to their soilless culture system. It is reported that nearly half the amount of water is required for tomato production in a soilless culture in a greenhouse compared to an open field, e.g., 24.2 L kg−1 in a greenhouse and 42.8 L kg−1 in an open field [82,83]. In the open fields, an average of 200 ± 100 L of water is required to produce one kilogram of tomatoes; however, about 60 L is necessary for the same amount of tomatoes when drip irrigation is used [84,85,86]. These performances are mainly due to modern soilless culture systems with a closed-loop irrigation system and reduced evapotranspiration in plant factories [81,87].
Water use in agriculture is critical in addressing food security on a global scale, particularly in regions where water scarcity poses significant challenges [88,89]. In hydroponics, a cascade system conserves water, captures excess nutrients, reduces waste, and minimizes environmental impact. Integrating water treatment, filtration, and nutrient recapture, a cascade system contributes to sustainable farming practices that enhance productivity while mitigating water and resource depletion [90,91].
Plant factories’ water use efficiency can be improved through adequate microclimate management and the ability to reuse water collected from the dehumidification system [91]. Air moisture from plant transpiration can be harvested through condensation and used for irrigation [92,93]. The harvesting of air moisture decreased water use by 67% and increased water use efficiency by 206% for lettuce production [53]. Orsini et al. [81] showed that when water was recovered by a dehumidifier and used for irrigation, the water use efficiency increased at least twofold. It is also acknowledged that sophisticated cultivation methods and thorough culture schedules catered to the requirements of the crop improve WUE [81,94]. Plant factory growing conditions can decrease the water required for the plant [95]. Carotti et al. [54] demonstrated that the water use efficiency for ebb-and-flow and aeroponic systems was 28.1 and 52.9 g L−1 H2O, respectively. Thus, the aeroponic system is about twice as efficient as the ebb-and-flow system [54]. Moreover, optimized aeroponics have reduced weight because they do not use growing media, showing further promise in such systems [75].
Aquaponics is another growing system (growing fish in nutrient tanks) for plant and fish production [96]. These systems are globally recognized for their production efficiency, quality, and food safety. Most aquaponics systems operate in a single-loop design, sharing and recirculating nutrients and water among all sections, including the vegetable production bed, fish tanks, and mechanical and biological filters [97]. Aquaponics reduces water consumption and repurposes waste from aquaculture [98]. This production system has been extensively studied and proven to be one of the most sustainable food production systems. Energy synthesis and life cycle assessment indicate that infrastructure materials are urban aquaponics’ main environmental and economic challenges. Practical strategies such as using rainwater instead of municipal water and replacing wood with iron in infrastructure can improve sustainability by up to 40% [56].

5. Energy Utilization by Humidity, Ventilation, and Air Conditioning

The local climate significantly affects the energy consumption of humidity, ventilation, and air conditioning (HVAC) systems in CEA, making site selection critical for energy efficiency [40,44]. Weidner et al. [29] evaluated the energy usage of a CEA. They found that cooling demands increased significantly when moving from colder regions like Reykjavik to hotter areas like Singapore and the UAE. For example, the specific energy needed for mechanical cooling in Reykjavik was less than 15 times that of the UAE. HVAC is the essential component of a CEA, and 25–30% of operational costs go to HVAC [99]. Advanced control systems that monitor and adjust humidity levels in real time can help minimize energy usage while ensuring optimal conditions for plant growth. The relative humidity is affected by the temperature of the air because plants constantly release moisture into the atmosphere through transpiration.
Ventilation is a crucial component in maintaining CEA air quality and temperature. Air exchange occurs between the indoor and outdoor environments, to remove excess heat, humidity, and pollutants while supplying fresh air [100]. Humidity control systems in CEA typically involve using humidifiers and dehumidifiers to adjust the moisture content of the air. Energy utilization for ventilation can vary depending on the type and size of the greenhouse.
Natural ventilation utilizes passive methods, such as windows, vents, or architectural designs, to circulate air without mechanical aid. As a result, it is far more energy-efficient, reducing the demand for mechanical systems and lowering energy consumption [101]. However, natural ventilation is dependent on external environmental conditions like wind, temperature, and humidity, and may not always provide adequate airflow or temperature control, particularly in extreme climates. This can lead to inconsistent indoor comfort levels and potentially increase the need for supplementary mechanical systems, negating some of the energy savings. However, mechanical systems provide more precise control over the internal environment, which can be critical in urban settings where space is limited and environmental conditions can be challenging [102]. Mechanical systems rely on fans, ducts, and sometimes heating or cooling elements to circulate air. Although these systems can efficiently filter and regulate indoor environments, they consume a significant amount of energy, especially in climates requiring extensive heating or cooling. This can lead to higher energy bills and a larger carbon footprint, making energy efficiency a key concern for mechanical ventilation. To optimize energy efficiency, hybrid ventilation systems, which combine both mechanical and natural methods, are often used. These systems can reduce energy consumption by relying on natural ventilation when conditions are favorable and switching to mechanical systems only when necessary. However, the initial setup and controls for such systems can be complex and costly [103].
Ventilation also controls humidity, which is vital for plant growth, nutrient and water uptake, and disease reduction. However, in tropical environments, the inside temperature is often higher than the outside, especially during warm seasons when cooling is most needed. Design factors such as the ratio of vent opening area to ground area, greenhouse volume to floor area, and vertical distance between air inlets and outlets are needed to optimize air exchange in high solar radiation [104]. Air distribution, air exchange capacity, and the static pressure differential that powers the ventilation are the main factors to consider when assessing a greenhouse’s mechanical ventilation system. Uneven temperature distribution can pinpoint problem regions using airflow visualization techniques [102]. Forced ventilation expedites air exchange and removal of the excess air by fans or blowers. Forced ventilation controls the even distribution of CO2 and high VPD and maintains lower temperatures [105]. This approach allows the intake air to be mixed and distributed more homogeneously inside the greenhouse [106]. Moreover, unlike natural ventilation, forced ventilation is not dependent on buoyancy or wind forces [107]. Forced ventilation, using mechanical fans or blowers and an air distribution system, provides better control over ventilation rates and ensures more uniform climate conditions inside the CEA [48].
Air conditioning systems provide precise temperature and humidity control in CEA, especially in regions where extreme weather conditions exist. Energy-efficient greenhouse air conditioning systems often incorporate variable speed drives, high-efficiency compressors, and advanced control systems to optimize performance and reduce energy consumption [46]. Integration with renewable energy sources, such as solar panels, can further enhance the sustainability of these systems [108,109]. Cooling pads are combined with ventilation systems to lower the temperature inside greenhouses [110]. The energy consumption of cooling pad systems depends on the size of the pads, the volume of water circulated, and the fans used to draw air through the pads.
Compared to a naturally ventilated glasshouse, a temperature differential of up to 11.6 °C was observed in a glasshouse fitted with evaporative pads; however, when utilizing a fog system, this difference was only 10.4 °C [111]. The pad-fan system’s primary flaw was its horizontal temperature gradients, varying from 11.4 °C between the pads and the fans. When operating continuously for an hour, the fog system needed more energy (7.2–8.9 kWh) than the pad-fan system (5.1 kWh). Unlike fog systems, which frequently require osmosis systems to prevent nozzle blockages, cooling boxes function independently of wind speed and do not require high-quality water. The cooling chamber’s packing material is essential for adequate heat and mass transfer because it offers a broad contact surface for quickly mixing water and air [112]. In plant factories, the envelope, such as sidewalls, roof, and floor, belong to traditional designs that enhance insulation to reduce reliance on external environments. However, too much insulation can trap heat, raising cooling demands and energy consumption.
The consistent and sufficient solar radiation in the desert southwest can readily generate sustainable electricity using traditional photovoltaics. The global horizontal irradiance over the southwest of the USA shows consistency with a daily mean ranging between 5.2 and 6.0 kW m−2. The photovoltaic power potential in these regions is 5.0–6.0 kWh/kWp daily, indicating the capacity to generate solar energy (Figure 3A,B). Urban agriculture in these regions is needed to reduce energy demands, particularly from cooling. Currently, greenhouses in the desert southwest USA incorporate several energy-saving techniques to combat the harsh climate and energy costs ensuring sustainability including passive solar design with thermal mass walls and natural ventilation to stabilize indoor temperatures, reducing reliance on artificial heating and cooling. Insulation, such as polycarbonate panels, helps minimize heat loss. Smart automation systems monitor and adjust conditions like temperature and humidity in real time, improving energy and water efficiency. Additionally, solar-powered fans and misting systems lower indoor temperatures without using grid electricity, making desert greenhouse production more energy efficient and sustainable [113]. Combining low-energy cooling systems with heat-reducing, energy-generating technologies will enhance CEA operational efficiency and facilitate their use in extremely hot regions.

6. Future Recommendations

Designing an Urban Plant Factory in the Desert Southwest

Urban farming is an uninterrupted, large-scale plant production system that operates throughout the year, which can reduce or completely avoid the effects of climate and environmental factors. This method guarantees a steady supply of fresh produce year-round, turning plant cultivation into a factory-like process. Due to energy costs and socioeconomic aspects, new energy-saving, controlled-environment plant production techniques are proposed to reduce greenhouse gases [115]. There are three designs of plant factories proposed: a 100% sunlight-based model, a sunlight and artificial light blended model, and a solely artificial-light-dependent model [31]. An effective way to utilize solar radiation in a plant factory in the southwest desert is needed to balance the abundant sunlight with effective heat management. Key strategies include using high-performance glazing and diffused glass to reduce heat gain while maximizing light transmission. Passive solar design and thermal mass help regulate temperature. Active solar energy systems, like photovoltaic panels and solar thermal collectors, can power and heat the plant factory. Renewable energy utilizes greener energy, potentially reducing costs and carbon emissions. Energy sources like photovoltaic panels, wind turbines, and small nuclear plants can be used for off-grid plant factory operations. Climate control with automated shading, natural ventilation, and evaporative cooling would be a heat management strategy.
Specialized LEDs provide precise control over light distribution and intensity, particularly effective for plant photosynthesis and energy savings. These systems offer customizable beam angles and shapes, ensuring uniform light coverage and targeted parts of the plant. These lenses improve energy efficiency and plant growth while allowing flexibility and scalability in different growing environments. These advanced emitting diode-light systems enhance the effectiveness of lighting in controlled agricultural settings.
An aeroponic system in a greenhouse in the desert southwest is an efficient and innovative way to grow plants while conserving water. In this soilless method, plant roots are suspended in the air and sprayed with a nutrient solution, making it ideal for the region’s arid conditions. Aeroponics employs up to 90% less water than traditional methods and supports faster plant growth due to high oxygen levels and direct nutrient delivery. The system is space efficient, reduces pest and disease risks, and can be powered by solar energy, making it sustainable and versatile for growing various crops.

7. Conclusions

Controlled-environment agriculture in the southwest of the USA holds significant promise for addressing food security, economic development, and sustainability challenges. Urban farming is a promising solution for continuous, large-scale plant production that addresses climate and environmental challenges. This method offers significant benefits over traditional farming practices by ensuring a steady supply of fresh produce year-round. The development of new techniques, including advanced plant factory models and energy-efficient systems, further enhances the sustainability of urban farming. Specifically, combined sunlight and artificial light systems provide flexible energy-saving options for building-integrated plant production systems. Employing advanced glazing, passive solar design, and active solar technologies like photovoltaic panels optimizes the use of solar energy, whereas specialized LEDs improve light efficiency and enhance plant growth. Additionally, an aeroponics irrigation system is well-suited to arid climates. Collectively, these strategies contribute to reducing energy costs, greenhouse gas emissions, and resource consumption, making urban farming a viable and sustainable approach for future agricultural practices.

Author Contributions

M.O.K.A. designed and drafted the original manuscript; N.S.G. improved the scientific soundness, added new content, reviewed and edited; M.T.N. Conceptualization, reviewed and supervised. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the United State Department of Agriculture (USDA) Multistate Project—NE2335: Resource Optimization in Controlled Environment Agriculture.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Ecological classification of the desert southwest, USA [4].
Figure 1. Ecological classification of the desert southwest, USA [4].
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Figure 2. The January 2020–August 2021 (a) precipitation rank and (b) temperature rank relative to equivalent January–August 20-month periods since 1895 from NOAA’s Monthly U.S. Climate Gridded Dataset (NClimGrid) [11].
Figure 2. The January 2020–August 2021 (a) precipitation rank and (b) temperature rank relative to equivalent January–August 20-month periods since 1895 from NOAA’s Monthly U.S. Climate Gridded Dataset (NClimGrid) [11].
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Figure 3. Horizontal irradiation (above) and photovoltaic electrical potential (down) of the United States of America. Adapted from https://solargis.com/ [114].
Figure 3. Horizontal irradiation (above) and photovoltaic electrical potential (down) of the United States of America. Adapted from https://solargis.com/ [114].
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Table 1. Distinguishing features of the glasshouse and plant factory.
Table 1. Distinguishing features of the glasshouse and plant factory.
ParametersGlasshousePlant Factory
Energy source Primarily relies on natural with supplemental artificial lightingUtterly dependent on artificial lighting
Energy efficiency (Electric and Fossil fuel)Generally, less energy efficientHighly energy efficient
Growing environmentSemi- and fully controlled environmentFully controlled environment, allowing precise management of environmental parameters
Production timeIdeal for crops that can thrive with seasonal variation Suitable for year-round production
Production methodMostly single-layer production Mostly multilayer vertical stacked production
Production density Low density per unit areaHigh density per unit area
External environment Influenced by the external weatherLess influenced by the external weather
Carbon footprint Carbon footprint is lowerCarbon footprint is higher
Operating costLower cost and less energy intensive Higher cost and energy intensive
Outlook/structureSingle glass structure Single- or multistory building envelope
Table 2. Major energy consumption and energy reduction factors of controlled-environment agriculture.
Table 2. Major energy consumption and energy reduction factors of controlled-environment agriculture.
Energy Consumption and Reduction FactorsResearch SummaryPotential StrategyReferences
Energy efficiencyThe use of energy and the carbon footprint are substantially elevated.A precise energy simulation model can reduce the energy costs.[44]
Controlled-environment agriculture is energy intensive. The energy cost depends on the facility’s location and the external environment.Appropriate design of the production methods for the specific location enhances the energy efficiency.[39,45]
Artificial lighting Lighting consumes up to 70% of electricity-controlled environment agriculture applications.A novel targeted light strategy can improve lighting efficiency.[46]
Façade design for solar lightTransparent façades enhance energy efficiency by utilizing natural solar energy instead of artificial lighting, reducing electricity consumption by 9.4% in the the UAE, 7.6% in the Netherlands, and 7.4% in Sweden. Façade design reduces energy demand.[31]
Harvesting solar cellIntegrating low-energy cooling systems with transparent infrared-harvesting solar cells that enhance energy generation and reduce temperatures.Low-energy cooling and infrared-harvesting solar cells increase solar energy efficiency. [45]
Ventilation Ventilation increases energy consumption by 18.4%, and on-off ventilation at a rate of one air renewal per hour increases energy consumption by 12.6%. Modeling and simulation of the dehumidification ventilation process reduce the greenhouse energy cost. [24,42,47]
Humidity and temperature control Dehumidification via controlled condensation recaptures latent energy for greenhouse heating, while hygroscopic materials convert condensation heat into usable warmth, lowering humidity and energy use.Adsorption of water vapor using hygroscopic material for the dehumidification process reduces operational costs.[48]
Temperature and humidity are crucial greenhouse controls that affect crop yield and energy use. Combining traditional control methods with AI algorithms has become a trend to reduce energy consumption and optimize greenhouse climates for crops.Numerical simulation and artificial neural network algorithms are strategies to reduce energy consumption.[49]
The pad-fan systems, fogging systems, and shading screens are effective processes for reducing the greenhouse temperature.The evaporative pad cooling system maintains more favorable conditions [50]
Greenhouse heating The solar rock bed (SRB) is the most effective energy-saving method in hot semi-desert areas. The night curtain system performs best in other climate zones, demonstrating climate sensitivity by lowering heating demand by 12% in very cold mountainous regions and 32% in dry climates.Solar rock bed modeling is the most effective system for reducing greenhouse heating costs.[51]
A different model for the energy efficiency Energy model algorithms such as the state space model, SQP, transfer function model, hybrid control, intelligence control, adaptive control, feedback, and feedforward control for the specific crop are essential strategies for reducing energy costs. Advanced control algorithm model increases energy efficiency. [38]
Hydroponic production Advances in platforms like Raspberry Pi and Arduino, along with new sensors and actuators, are set to revolutionize precision agriculture, making controlled-environment farming more affordable and efficient for small-scale producers.Hydroponic system increases water use efficiency. And aeroponic system is more water-efficient than hydroponic practices.[52,53]
Closed-loop systems save 40% of irrigation water and 35–54% of nutrients while reducing eutrophication, but they may cause nutrient deficiencies and require more infrastructure, raising environmental impacts.A closed-loop system is the most efficient for irrigation.[54,55]
Aquaponics enhance sustainability by mimicking natural processes in a controlled system, making it suitable for urban areas with limited agricultural land even though it is environmentally friendly.Aquaponics is a sustainable production system.[56,57]
The water use efficiency of aeroponics systems is higher than that of hydroponic systems.[53]
Solar energy Solar energy can aid climate mitigation, and photovoltaic energy may reduce this competition and provide benefits across the food–energy–water nexus. Photovoltaics enhance solar power efficiency and renewable energy application[58]
The presented table analyzes energy consumption and efficiency strategies in controlled-environment agriculture (CEA). Key points include the high energy use and carbon footprint of CEA, with potential savings through tailored production methods and energy simulation models. Efficient lighting and façade designs, such as transparent façades and solar cells, can significantly reduce energy demand. Optimizing ventilation, using AI for climate control, and employing solar rock beds for heating also enhance efficiency. Hydroponic and aeroponic systems improve water and nutrient use, and aquaponics offers a sustainable solution. Integrating solar energy further boosts efficiency, addressing climate challenges and resource management.
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Azad, M.O.K.; Gruda, N.S.; Naznin, M.T. Energy Efficiency of Glasshouses and Plant Factories for Sustainable Urban Farming in the Desert Southwest of the United States of America. Horticulturae 2024, 10, 1055. https://doi.org/10.3390/horticulturae10101055

AMA Style

Azad MOK, Gruda NS, Naznin MT. Energy Efficiency of Glasshouses and Plant Factories for Sustainable Urban Farming in the Desert Southwest of the United States of America. Horticulturae. 2024; 10(10):1055. https://doi.org/10.3390/horticulturae10101055

Chicago/Turabian Style

Azad, Md Obyedul Kalam, Nazim S. Gruda, and Most Tahera Naznin. 2024. "Energy Efficiency of Glasshouses and Plant Factories for Sustainable Urban Farming in the Desert Southwest of the United States of America" Horticulturae 10, no. 10: 1055. https://doi.org/10.3390/horticulturae10101055

APA Style

Azad, M. O. K., Gruda, N. S., & Naznin, M. T. (2024). Energy Efficiency of Glasshouses and Plant Factories for Sustainable Urban Farming in the Desert Southwest of the United States of America. Horticulturae, 10(10), 1055. https://doi.org/10.3390/horticulturae10101055

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