Vertical farming is a promising approach to help feed a growing world population using little water and land area. An IoT-networked prototype is used to demonstrate the technology to optimize lighting, irrigation, fertilization and climate control to achieve the highest yields and best quality.
A world population projected to be almost 10 billion by 2050 will require a 50 percent increase in global agricultural production, according to the UN Food and Agriculture Organization (FAO). Yet agricultural land has actually declined in recent decades, from nearly 40% of the world’s land area in 1991 to just 37% in 2018 [1]. To counteract these challenges, we need solutions. Part of this solution can be ‘Controlled Environmental Agriculture’ (CEA for short). This also includes ‘indoor vertical farming’. In ‘vertical farms’, fresh, nutritious food can be grown locally for people, e.g., in urban areas. This method of growing is also possible in regions of the world where conventional agriculture would not work. It supports traditional agriculture and does not compete with it.
These modern multi-level digitized greenhouses can only be successful if several key technologies like lighting, control and monitoring are mastered.
The most obvious advantages of indoor vertical farming are its small footprint, up to 95% less fresh water use, and energy savings up to 70% if energy-saving LED technology is used. Würth Elektronik offers a wide range of ‘horticulture LEDs’ [2] whose color spectrum is ideally matched to plant requirements. It also conducts its own research in this area to further establish suitable dynamic lighting recipes for the market [3].
A sample kit with horticulture LEDs and wireless connection exists to create optimal lighting conditions and keep energy consumption low with intelligent lighting control and optimized power supply [4, 5]. More on the subject of horticulture LEDs and their application can also be found in [6] to [11].
Besides optimal light conditions, other environmental factors are also important for plant growth including, the temperature, humidity or even the soil moisture. These parameters must be monitored, controlled and dynamically optimized.
The Internet of Things to automate agriculture
Complex automation, such as the smart factory of Industry 4.0, smart buildings, or even new agricultural concepts, require sensors and devices to be networked in an Internet of Things (IoT). We explain in the following how the use of horticulture LEDs and implementation of remote monitoring and control for plant growth in vertical farms can be realized quickly and cost-effectively using rapid prototyping tools. Fig.1 shows the prototype of an indoor farming box. All critical components of the prototyping solution are available from a single source, from Würth Elektronik.
The core task of any IoT solution is to transfer data from the field to the cloud, where it is analyzed to generate the desired added value for the application. An open-source hardware and software ecosystem was used and a complete IoT solution was created for this application. To this end, Würth Elektronik has combined Adafruit’s Feather M0 Express board with its own FeatherWings, i.e., the Feather form-factor development boards with various sensors, radio and power modules, LEDs and LED drivers and components (Fig. 2). Here the basic idea is to create a digital system that optimizes growth, on the one hand, and electricity and water consumption, on the other.
Controlled irrigation and lighting
The prototype consists of a vertical farming structure based on a soil substrate combined with a 4-channel LED driver and a horticulture LED design kit that makes it easy to mix the required light spectra to promote plant growth under different lighting situations. The drip irrigation system and water tank use recycled water whose pH and electrical conductivity (EC) (salinity) are measured, controlled and transmitted to the cloud through multiple communication modules from Würth Elektronik. A soil moisture sensor monitors soil moisture and a small pump supplies water to the system, if required. The excess water is collected, filtered and returned to the tank. The heart of the system is Adafruit’s Feather M0 Express board with relay wings used as switches. Data is sent to the cloud, where the information is processed, analyzed and used to control the farm.
Lighting system
The lighting system (Fig. 3) consists of a horticulture LED panel with four separate channels including special single-color horticulture LEDs, and the MagI³C multi-color LED driver. Both are included in the Lighting Development Kit from Würth Elektronik [2]. The LED driver with the MagI³C series step-down power module allows individual adjustment of the intensity and color of each of the four LED strands to meet the application requirements and match the light recipes to the plant profile. The horticulture panel consists of six hyper-red (660 nm), four far-red (730 nm), two deep-blue (450 nm) and four white ceramic LEDs. The system can be controlled via Bluetooth, WiFi or a cell-phone connection.
Irrigation
The water tank filling level is measured with the WSEN-PDUS differential pressure sensor. This is a very accurate MEMS piezoresistive sensor (Fig. 4). In addition, a 12 V pump moves the nutrient-rich water into the drip tray via a flow sensor. Water quality is monitored with the DFR-05874 (pH) and DFR-0300 (EC) meters from the DFRobot Gravity series. Most natural bodies of water have a pH value between 5 and 8. The generally accepted pH for irrigation water is between 5.5 and 7.5, but the best results were achieved with pH values between 5.5 and 7. Water in this pH range maintains its nutrient balance, provides effective chemical disinfection, and prevents calcification in irrigation systems [12]. ‘Fertigation’ is a blend word of fertilization and irrigation. As a result of the small substrate surface area, growing in substrates requires good irrigation and a lot of fertilizer, which is added to the irrigation water. An EC meter is used to detect an undersupply or oversupply of fertilizers in the irrigation water. Electrical conductivity (EC) is a measure of the concentration of ions in water and serves to measure the ability of water to conduct electricity. The purer the water, the lower the conductivity. The capacitive STEMMA soil sensor from Adafruit was used to measure soil moisture. Capacitive measurements use only one probe; there is no exposed metal that can oxidize, and no DC current is passed into plants. The pump is controlled automatically and directly via the cloud. Its operating time is calculated based on the number of plants, required soil moisture, and the pump flow rate (Fig. 5).
Acquiring environmental data
Carbon dioxide is required in large quantities for enrichment and extraction processes. These processes accelerate the growth of plants and CO₂ serves as a fumigant. In enrichment, a CO₂ content of 800 to 1500 ppm is usually set to accelerate growth by 20 to 30%. Increasing overall metabolic rate helps plants withstand the effects of heat. Larger, healthier and more robust plants tolerate extreme environmental influences better. An increased plant metabolic rate means additional requirements, however. The plants not only need more water and nutrients, but also additional ventilation. The CO₂ content of the system was measured and monitored online using the Adafruit SPG30 air quality sensor connected to the Würth Elektronik FeatherWing sensor. It should be borne in mind that the sensor measures the equivalent CO₂ content. This eCO₂ value is calculated based on the H2 concentration, so it is not a ‘real’ CO₂ sensor for laboratory use. A plant requires different light and heat conditions at each stage of growth. Most plants tolerate normal temperature fluctuations, and the optimal thermal conditions for plant growth can vary, not only between the respective phases, but also throughout the day. Optimization can be achieved by measuring the temperature and optimizing the daily cycles. When the light is switched off, the temperature should be a few degrees lower. Humidity is specified as relative humidity. Different plant stages require different levels of humidity. An overly humid environment can raise the potential for spreading disease. Both humidity and temperature are monitored with the WE FeatherWing sensor.
Communication options
Sensors and actuators are usually installed in devices with limited connectivity to the digital world. Today, there are many standardized and proprietary wireless solutions, whose selection isdetermined by a number of factors such as transmission range, throughput, frequency bandwidth, local regulatory requirements and energy budget. The prototype’s communication is implemented using two different approaches, firstly with a Calypso WiFi FeatherWing (Fig. 6) for environments where WiFi is available, and secondly with an Adrastea-I FeatherWing (Fig. 7) for environments without WiFi. Both boards are connected to the rest of the system via the Adafruit Feather M0 Express board. The Calypso board is a compact WiFi radio module based on the IEEE 802.11 b/g/n (2.4 GHz) WiFi standard. It has an integrated TCP/IP stack and an out-of-the-box MQTT (Message Queue Telemetry Transport) protocol. The Adrastea-I module is a compact LTE-M/NB-IoT mobile module with integrated GNSS and an Arm Cortex-M4 processor suitable for every IoT application. Both modules are suitable for simple and secure connection to the cloud. In this case, the choice was made for an external M0 processor and, because of its simplicity and ease of use, Microsoft IoT Central, a Platform as a Service (PaaS). IoT Central has a ready-to-use user interface and API for connecting, managing and operating IoT devices. With its telemetry, features and commands, it has been used to monitor and control all aspects of the vertical growing system.
The prototype shows on a small scale how vertical farming works and is in itself an application. A similar cabinet produces fresh herbs in the Würth Elektronik canteen. The electronic components of the prototype, from microcontroller control, communication with the cloud, to the power supply and LEDs, all come from a single source, Würth Elektronik.
About the Authors:
Alexander Gerfer is Managing Director and Chief Technology Officer of one of Europe’s largest manufacturers of electronic and electromechanical components. The graduate engineer (University of Applied Sciences) in Electrical Engineering and trained radio and television technician has been with Würth Elektronik since 1997 and started his career classically as a technical sales representative. The starting point for today’s eiSos Group product range was his knowledge of the many unanswered questions surrounding inductive components, as well as his practical experience in power management, and the need for standardized power inductors and suppressor ferrites. He is instrumental in building the company’s research and development as well as product, quality and supply chain management. Alexander Gerfer is a textbook author, lecturer and in-demand keynote speaker. With his experience and credo, he has helped shape the development and orientation of Würth Elektronik eiSos as a service-oriented manufacturer and promoter of technology.
Adithya Madanahalli graduated from the Technical University of Munich with an MSc in Communications Engineering. He went on to work for several years as a software engineer in the field of wireless connectivity and sensors. Since 2022, Adithya Madanahalli has been working as an IoT engineer at Würth Elektronik eiSos in the Wireless Connectivity and Sensors business unit. Here he is specialized in the design and development of IoT solutions with a focus on hardware, embedded software and end-to-end security.
Johann Waldherr graduated from the Technical University in Munich and Humboldt University in Berlin with a MSc. in Horticulture Science. He then worked for several years as a plant researcher, with a focus on how different wavelengths of the light influence different quality parameters of the plant. Since 2017, Johann has been a Business Development Manager for Horticulture LEDs at Würth Elektronik eiSos in the business unit eiPal Optoelectronic. There he specializes on the biological, optical and electrical parameters in the field of Vertical Farming and Horticulture Lighting. He supports the development of light concepts in the area of plant lighting.
