This study aims to develop a PV-driven smart islanded microgrid capable of managing both critical (such as heating inside the electric panel in cold climates) and shiftable (such as LED light bulbs) loads. The main advantage of the proposed prototype is its affordability as it utilizes two Arduino Uno microcontrollers that are available worldwide, along with a photoresistor for measuring light intensity and two relays for connecting/disconnecting the shiftable load and minimizing the time without the power supply of the critical demand. The control algorithm is based on three-input hysteresis with the counter of loops in Arduino sketch with high intensity of light (over 1002 - direct sun rays; the counter is incremented if the load has a power supply on the solar charge controller) and the correcting variable that doubles once per 24h if the load is OFF on the solar charge controller: the shiftable load is ON while the counter is positive during the night time; the value of correcting variable is subtracted from the counter. Arduino Uno microcontrollers transmit data via I2C protocol. Experimental results conducted at the Naryn campus of the University of Central Asia in Kyrgyzstan have shown that the proposed microgrid prototype minimizes the time when the critical load is OFF and allows limited power supply to the shiftable load.
The islanded microgrid (µG) driven by photovoltaic (PV) energy [
Numerous commercial products and prototypes, such as the West Virginia Super-Circuit
project with multiagent system architecture [
This study presents the ad hoc project, the solar electric system with two power lines at the Naryn campus of the University of Central Asia in Kyrgyzstan. The Naryn region is well-known for its low ambient temperatures (sometimes -400C) during the cold season, and hence the outdoor installation of the µG control equipment requires the internal heating of the electric panel. Therefore, two power lines must be installed: one for the heater, which is critical, and the other for the shiftable load, which in this prototype is a 12 V / 10 W light-emitting diode (LED) light bulb. The shiftable load is turned on if there is enough power generated by the solar panel and the photoresistor value is below the predetermined threshold value; it is turned off otherwise, i.e., the demand side energy management [12] should be implemented. The hysteresis switching adaptive control algorithm uses three inputs to manage the shiftable load with the Arduino relay [13, 14]: the current light intensity from the photoresistor, the counter of loops in the Arduino sketch with high intensity of light (direct sun rays) measured by the photoresistor, and the solar controller discharge stop voltage. Two Arduino Uno microcontrollers communicate via the Inter-Integrated Circuit (I2C) protocol [15, 16]. The architecture of the proposed PV-driven smart islanded µG is shown in Figure 1: Arduino Uno microcontrollers use 5 V relays to connect / disconnect power lines; the emergency power supply, which is not discussed in this study, is an independent source of electrical power that supports the critical load (the heater in this study) on the loss of normal power supply from the solar charge controller; other equipment is discussed throughout the paper.
The main contribution of this study is the development of an affordable solar electric system with two power lines, for the critical demand (the portable heater in this study) and the shiftable load (the LED light bulb in this study), adapted to the environment with low ambient temperatures like the Naryn region. Analysis of existing commercial products shows that the presented low-priced prototype of µG with the adaptive control algorithm and the hardware based on the 100 W solar panel, 30 A solar charge controller, and two Arduino Uno boards connected via the I2C protocol to manage critical and shiftable loads does not have analogs under USD 100 on the market.
The number of Web of Science papers related to µGs has significantly increased from 2010 to 2021 [10]. Many papers, such as [6, 12], discuss the design and analysis of µGs employing simulation tools like Matlab / Simulink. However, this study focuses on the physical implementation of μG, with the goal of improving the power supply system for critical loads and minimizing power loss while providing electric energy to the shiftable demand. This approach emphasizes the use of IoT soft-/hardware and control algorithms.
The open-source Arduino-based soft-/hardware, such as Arduino Uno
[9, 11] / Mega [
In [
Analysis of previous studies shows that µG is built according to the existing infrastructure, customer needs, and various load types, and hence it should be capable of operating under varying power grid conditions. Therefore, there is no fixed cost and / or structure for µGs, but the minimization of expenses is the priority for customers.
Relays (HW-482 in this study) [10, 13] are commonly used to connect / disconnect DC and AC power lines, regardless of the type of control technique. The relay 2 (see Figure 2) position, whether ON or OFF, depends on the control algorithm, which is based on a three-input hysteresis system in the µG prototype: 1. If the photoresistor value, i.e., the light intensity, is less than 300, then the normally closed pin is ON. If the photoresistor value is greater than 350, then the normally closed pin is OFF. 2. If the counter of the photoresistor values over 1002 (direct sun rays) is positive, then the normally closed pin is ON; otherwise, it is OFF. 3. If the lead-acid battery voltage is less than 10.7 V (the discharge stop voltage measured by the solar charge controller), then the normally closed pin is OFF; otherwise, it is ON.
The third condition is implemented without the DC voltage sensor since it consumes additional power using the voltage divider technology. When the battery voltage drops to 10.7 V, the loads are disconnected, and as a result, the Arduino Uno microcontroller (I2C peripheral receiver) connected to the solar charge controller does not have the power supply required to operate. Because of that, another Arduino Uno microcontroller (I2C controller writer) is unable to send data. This setup allows the I2C controller writer to detect whether the loads have a power supply or not. Additionally, the Arduino I2C peripheral receiver is used as a terminal to access the data on the Arduino I2C controller writer: if the power supply is OFF or the serial monitor starts in Arduino IDE, then the sketch is reloaded on Arduino Uno microcontroller. After analyzing the related works and considering the prototype requirements, the proposed bare µG wiring is presented in Figure 2.
Figure 2 shows that the solar charge controller receives the power from the 100 W monocrystalline solar panel and then distributes it between the battery and the load. The discharge stop voltage is 10.7 V, the discharge reconnect voltage is around 11.5 V (experiments showed that it varies between 11.2 V and 11.5 V for the controller W88-C), and the equalization voltage is 14.4 V as four lead-acid batteries are employed in the prototype. The Arduino I2C controller writer is powered by a 12 V power supply from the batteries, which means it is always ON. It is connected to the Arduino I2C peripheral receiver through pins SCL (a serial clock pin), SDA (a serial data pin), and GND (ground). The Arduino I2C peripheral receiver is powered by a 5 V power supply from the solar charge controller USB port and is only ON when the load has a power supply on the solar charge controller. The relays are powered by the Arduino I2C peripheral receiver, and hence they are disconnected if the load is OFF on the solar charge controller. Relay 1 input is the digital pin 8 on the Arduino I2C peripheral receiver. Relay 2 input is the digital pin 7 on the Arduino I2C controller writer. The shiftable load is the 12 V / 10 W LED light bulb. The critical load is the portable 5 V heater. The photoresistor connected to the analog pin A0 on the Arduino I2C controller writer measures the light intensity: the value over 1002 represents the direct sun rays. MicroSD card module is employed to save the data used in calculations; its pins CS (Chip Select), MOSI (Master Out Slave In), MISO (Master In Slave Out), and SCK (Serial Clock) are respectively connected to digital pins D4, D11, D12, and D13 on the Arduino I2C controller writer.
The research question is what heater power is needed to keep the temperature above 0 0C inside the electric panel. The assumption is that 0 0C is the normal temperature for the prototype hardware and that the electric panel is winterized (i.e., heat insulation is added internally and/or externally) and has dimensions 0.5 m×0.5 m×0.3 m=0.075 m3. In general, 1000 W is suitable for heating a space of 25 m3, and hence 4 W, the power provided by the portable 5 V / 3.5 W heater and the hardware inside the panel, should be enough for 0.1 m3 which is larger than the discussed volume of the electric panel (0.075 m3). Table 1 presents the approximate power consumption of 4.3 W for two Arduino Uno microcontrollers (measured by the USB charger tester) and other equipment inside the electric panel in the presented prototype.
In the presence of critical and shiftable loads, the specified amount of total energy is expanded [17], which is characterized by the following relations on each day: , + (1 − ) , ℎ ≤ ≤ , the time step around 1.8 s at the Arduino sketch loop function resolution, critic and shift for the demand response, and represent the critical and shiftable loads,
= {0,1} is the decision of engagement, DR stands is the maximum power energy that can be generated for 24h.
depends on the amount of power energy received from the solar panel: = 0, 24 > 0; 1, ℎ , where 24 is the counter of loops in Arduino sketch with high intensity of light (over 1002 – direct sun rays; the counter is incremented if the load has a power supply on the solar charge controller) measured by the photoresistor.
The flowchart for the µG shiftable load management (i.e., relay 2 is ON or OFF) using the hysteresis with three inputs is shown in Figure 3. is the correcting variable that doubles once per 24h if the load is OFF on the solar charge controller. the flowchart in Figure 3, which are calculated out of the presented algorithm. and 24 are two inputs for
– the USB charger tester and the digital multimeter QHTITEC 830Plus. Two Arduino Uno boards in enclosures were prepared for the outdoor installation. In future, the equipment is going to be installed outdoors inside the electric panel, and it will work with two 330 W solar panels (see Figure 5; the photo was taken at the Naryn campus of the University of Central Asia in Kyrgyzstan on December 12, 2023). These solar panels will be reinstalled to change their position on the roof of the summerhouse because they get covered with snow during snowfall.
No No No No
Relay 2 is OFF The photoresistor value is less than 300
Yes respective decision elements on the right.
USB charger tester Solar panel
Photoresistor Two Arduino Uno boards in enclosures Portable 5 V heater (critical demand) LED light bulb (shiftable load)
The horizontal axis represents the dates of the experiment: days 1-14 correspond with March 6-8 and 11-21, 2024, respectively.
The right vertical axis represents the maximum number per day (blue line) of photoresistor values that are larger than 1002 (i.e., the direct sun rays). The left vertical axis represents the battery voltage (green line), the ON (1) / OFF (0) status of the load on the solar charge controller (red line), and the value of the correcting variable (black line). The measurements were taken hourly.
The experimental results show that the proposed control method with hysteresis and correcting variable effectively minimizes the time when the critical load (red line) is OFF and allows for the power supply of the shiftable load. The energy produced by this prototype is sufficient to power floodlights with a passive infrared (PIR) sensor.
16,0 14,0 12,0 10,0 8,0 6,0 4,0 2,0 0,0 1 1 2 2 2 3 3 4 4 4 5 5 6 6 7 7 7 8 8 9 9 9 101011111212121313141414
Days
In this study, a new µG prototype has been proposed for managing the critical and shiftable loads. The control algorithm is based on hysteresis with three inputs and adaptive adjustment of the correcting variable. Experimental results demonstrate that the approach proposed in this study is operable. However, the selection of hardware components, software, and control 7000 6000 5000 4000 3000 2000 1000 0 s e u l a v r so 002 t i s 1 e n r too tah h r p e
g fro lra e t n u o C algorithms used in the prototype are empirical and, therefore, open to discussion. In particular, two concerns were discussed in the Department of Computer Science at the University of Central Asia:
How the correcting variable is changed.
How the amount of the solar power energy is assessed using the counter of loops 24 in Arduino sketch with high intensity of light measured by the photoresistor.
A new PV-driven smart islanded µG is proposed in this study for managing critical and shiftable loads. The control algorithm employs a three-input hysteresis, I2C communication between Arduino Uno microcontrollers, analysis of solar energy using a photoresistor, and adaptive additive adjustment of the correcting variable. This system is shown to be operable under different weather conditions, such as cloudy or sunny.
The main advantage of the developed prototype is an affordable solar electric system with two power lines, one for the heater (critical load) and the other for the shiftable demand, adapted to low ambient temperatures. Analysis of existing commercial products shows that the presented low-priced prototype of µG, equipped with a 100 W solar panel, 30 A solar charge controller, and two Arduino Uno microcontrollers, has no analogs under USD 100. Experimental results from the Naryn campus of the University of Central Asia in Kyrgyzstan have shown that the proposed µG prototype minimizes the time when the critical load is OFF and allows limited power supply to the shiftable load. In this soft-/hardware configuration, the prototype can provide power to floodlights, equipped with a PIR sensor, which serves as the shiftable load.
The most likely prospect in developing this study is to design a box solution that is ready for outdoor installation.