Harnessing Sunlight: How a Tiny Panel Woke Up the Cortex-M — Part 3

February 23, 2024

Blog

This three-part series details a case study on the use of miniature solar panels in powering IoT Devices. Check out the bottom of the article for Parts 1 and 2!

Conclusion: The Objective Evaluation

Our research shows that photovoltaic panels can be useful in certain IoT scenarios.  In practical applications, compact solar panels show promise for a variety of IoT devices. For example, in smart agriculture, solar-powered sensors can monitor soil moisture and environmental conditions, leveraging sunlight available in open fields. In urban settings, solar energy can power smart parking sensors, which only require intermittent bursts of power. Additionally, in remote monitoring, such as wildlife tracking or forest fire detection, the minimal energy needs of these sensors align well with the capabilities of photovoltaic panels. Even in indoor scenarios, low-power devices like temperature or air quality sensors can function effectively in well-lit areas, utilizing indoor lighting. The key is to match the device's power requirements with the expected energy harvest from the PV panels, considering factors like device sleep modes and energy-efficient communication protocols.

However, their current capabilities are limited by daylight time and may not always provide reliable and continuous power for a broader range of IoT devices, especially in less ideal environmental conditions. But with the proper setup of the device's computing power algorithms, continuous operation solely on solar energy is feasible not only during daylight hours. Based on our study, we can draw important conclusions regarding the applicability of compact solar panels:

The Efficiency of Voltaic Panels

The Voltaic P121 R1L panel demonstrated high efficiency in strong sunlight, but its ability to sustain stable operation of IoT devices in less ideal conditions remains questionable. This is especially true if we want to use more complex device modes, where the IoT board's peripherals will be used more intensively, often with much higher power consumption.

The P122 R1J panel, while suitable for certain applications, has current limitations, particularly in less sunny weather, and may only be applicable in specific cases where the IoT device requires a combination of increased voltage with low current for rare and brief periods of peak activity.

Adaptability of the Epishine Module

This module proved efficient in low-light conditions, making it potentially suitable for indoor IoT applications. However, its ability to sustain long-term device operation without an additional power source is limited, especially considering variable indoor artificial lighting conditions. As with the Voltaic panels, uninterrupted power supply from a single module will primarily depend on the proper power consumption settings of the IoT device itself, to use its peripherals and performance capabilities only when truly necessary.

PV Panel Type	Epishine Light Energy Harvesting Module	Voltaic P121 R1L	Voltaic P122 R1J
PV Panel Characteristics	Optimized for 20-1000 lux, Output Voltage: 1.8V to 3.3V, Output Current: up to 300mA	Max Power: 0.3 W, Voltage: 5.9 V, Current: 60 mA	Max Power: 0.32 W, Voltage: 2.3 V, Current: 150 mA
Capacitor Type	Onboard GA230F 400mF CAP-XX SuperCapacitor	Voltaic C116 with Vinatech 250F VEL13353R8257G Capacitor	Voltaic C116 with Vinatech 250F VEL13353R8257G Capacitor
Capacitor Characteristics	Energy Storage: 1.9Ws at 3.3V to 3.4Ws at 1.8V	Output: 2.5 to 3.8 V, Capacity: 250 F	Output: 2.5 to 3.8 V, Capacity: 250 F
Indoor Performance	Efficient in low-light conditions. Stores up to 3.4Ws. Operational time with maximum NRF52832 load: ~35s at 3.3V, ~145s at 1.8V.	Maintains sufficient energy output indoors with artificial lighting.	Increased efficiency with the capacitor, providing continuous power to NRF52832 in low light.
Outdoor Performance	Maintained operation in outdoor sunlight. Efficiency confirmed in various lighting conditions.	Generated ~120 mA under sunny conditions, exceeding NRF52832's startup current of 70 mA.	Generated about 43 mA outdoors, insufficient to start NRF52832 without a capacitor.
NRF52832 Op Time with zero solar input (on the capacitor, hours)	More than 12	~6,5	~6,5
ATM3202 Op Time with zero solar input (on the capacitor, hours)	More than 18	~9	~9

Note: The operational time for each PV panel and capacitor setup without solar input (e.g., nighttime) was calculated based on the following working mode:

• Advertising Mode: The device enters this mode once per hour for 5 seconds.
• Connecting State: Immediately following advertising, the device operates in this state for 10 seconds.
• Sleeping Mode: The device is in a low-power sleeping mode for the remainder of the hour.

These consumption rates were used to determine the total energy usage per hour, which was then compared against the energy storage capacities of the capacitors paired with each PV cell.

Role of Capacitors and Batteries

The use of supercapacitors and additional batteries as auxiliary power sources proved crucial for maintaining 24/7 IoT device operation where PV panels cannot provide sufficient power supply. We believe that PV panels with such onboard capacities, combined with wide options for adjusting output current and voltage, have the most potential for further development and market expansion in the context of integrating one module into one IoT device.

Sirin Software: The Future and Prospects

In a market where IoT demands increasingly complex computing capabilities at the individual device level, research seeking the necessary balance between computational power and energy consumption will never end.

Solar panel manufacturers daily offer newer, more advanced, and efficient solutions. Such advancements will open up more opportunities for using miniature solar panels in IoT devices, inevitably leading to the exploration of utilizing greater computing power at the device level. Therefore, we see the ability to correctly select, configure, and even create IoT devices as a key factor in this endless race.

A testament to our commitment to this field is our recent success story. In this project, we provided a client with an innovative solar-powered IoT device for environmental monitoring in urban areas. This device, capable of measuring air quality, noise pollution, and weather conditions, represents a significant stride in our efforts to marry high-efficiency IoT solutions with renewable energy sources.

At Sirin Software, our goal is to develop IoT technologies that consume less energy while maintaining efficiency. This includes designing sensors and devices that work well with the energy provided by both current and future solar technologies. We continue to strive for future research to contribute to the development of renewable energy use for integrating eco-friendly technologies into our daily lives.

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Editor's Note: For more information, check out:

• Part 1
• Part 2