Supercapacitor Solar IoT for High-Power Actuation

Description

Most solar IoT systems can measure things.
Very few can do things.

This project shows a battery-free solar IoT system that runs for days without sunlight—and still delivers high-power bursts (9V–24V, up to 1.5A) to drive real-world actuators.

By storing energy in supercapacitors instead of batteries, it enables maintenance-free operation while bridging the gap between low-power sensing and high-power control.

Details

Overview

Heliotrax is a solar-powered, battery-less IoT platform designed for long-term outdoor operation. It enables reliable monitoring and control of sensors and actuators without the need for batteries or regular maintenance.

The system is built as a modular hardware platform for developers and system integrators, providing robust electronics and reference firmware while allowing full flexibility in software implementation.

The Problem

Many outdoor IoT systems rely on batteries, which introduce limitations in lifetime, reliability, and maintenance. In remote or hard-to-access locations, battery replacement becomes costly and impractical.

In addition, most solar-powered IoT nodes are designed only for low-power sensing. They can supply sensors requiring small voltages and minimal current, but are not capable of driving actuators.

There is currently a lack of compact systems that can:

harvest energy from small solar panels
store energy efficiently
deliver short, high-power bursts (e.g., up to 24V)

This limits the ability to control actuators such as latching solenoids, valves, or switching elements in autonomous outdoor system

The Solution

Heliotrax combines solar energy harvesting with efficient energy storage and controlled high-power delivery.

Energy is stored in two 22F supercapacitors connected in series, forming a storage stage up to 5V. The system accumulates energy over time and releases it as a controlled high-power burst when required.

This enables:

battery-less operation
long-term autonomous deployment
actuation of power-hungry devices

The platform bridges the gap between low-power energy harvesting and high-power actuation.

System Architecture

Transmitter Node (core hardware)

solar energy harvesting and storage
ultra-low quiescent current (~tens of µA)
sensor interfacing and data acquisition
controlled high-power output for actuators
wireless communication

Receiver Node

implemented on standard ESP32-C3 boards (e.g., XIAO, Dev Module)
receives data and triggers actions
requires only corresponding software

Performance & Technical Capabilities

Energy storage: 2× 22F supercapacitors (series, up to 5V)
Ultra-low quiescent current: a few 10 µA
No-light operation: up to ~5 days (foggy conditions, ultra-low-power mode)

High-power burst outputs:

24V @ 500 mA
12V @ 1 A
9V @ 1.5 A

Expandability:

Additional supercapacitors or Lithium-Ion Capacitors via screw terminals
External solar panel or alternative energy source input

Hardware Platform Features

Modular hardware design
7 Grove connectors for sensors and modules
Support for Grove ecosystem (e.g., LoRa modules)
Interface for SIM800L GSM/GPRS module
Designed for flexible integration and prototyping

Software Approach

Heliotrax follows a hardware-first approach.

The project provides:

reference firmware (Arduino-based PoC)
example implementations for transmitter and receiver

Users are expected to develop their own application software based on their requirements, ensuring full flexibility and independence from predefined ecosystems.

Why It Matters

Heliotrax extends the capabilities of autonomous IoT systems beyond sensing by enabling actuator control without batteries.

Key advantages:

maintenance-free deployments
operation in remote or hard-to-access locations
reduced environmental impact
ability to drive real-world devices (e.g., valves, relays, actuators)

This makes it suitable for applications such as:

water management systems
infrastructure control
distributed automation in outdoor environments

Documentation & Code

Reference firmware is available on GitHub: https://github.com/Nelectra/Heliotrax-reference-firmware

The repository includes transmitter and receiver implementations for testing and development.

Project webpage: https://heliotrax.io/

Technical Specifications

PCB No.1 – Control and Communication

Energy storage:

Onboard 2x supercapacitors 22F/2.8V
Expandable with an additional pair...

Files

j4g_24V1.pdf

Schematics for PCB No. 2: Power & Actuation

Adobe Portable Document Format - 419.58 kB - 04/24/2026 at 19:50

Preview

j4g1.pdf

Schematics for PCB No. 1: Control & Communication

Adobe Portable Document Format - 414.02 kB - 04/24/2026 at 19:48

Preview

spacers.stl

3D-printable spacers for spacing PCBs and aligning the solar panel.

Standard Tesselated Geometry - 941.63 kB - 04/24/2026 at 19:43

Download

Project Logs

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Day-Night Cycles

Nelectra • 15 minutes ago • 0 comments

A long-term measurement shows the typical charge and discharge behavior following day–night cycles. Even under cloudy conditions, the supercapacitors are charged close to their maximum voltage levels.

In this example, the ESP32-C3 operates in continuous deep sleep mode. Between February 19 and February 20, snowfall occurred in Bratislava, covering the solar panel. As a result, the supercapacitors could not be recharged for three days.

Despite this, the voltage did not drop below 4.1 V, demonstrating the system’s robustness under unfavorable environmental conditions.

Maximum Runtime Without Sunlight

Nelectra • 24 minutes ago • 0 comments

In a continuous deep-sleep scenario, the system can operate for several days without sunlight.

In this first experiment, a simplified firmware was used to keep the system in permanent deep sleep. The fully charged supercapacitors powered the ESP32-C3 through a DC/DC converter, operating down to an input voltage of approximately 1.5 V. Below this threshold, the converter disables output regulation and the ESP32-C3 can no longer maintain a stable supply.

Under these conditions, total runtime reached nearly 6 days.

This test demonstrates the feasibility of multi-day autonomous operation using only harvested solar energy stored in supercapacitors, without any battery buffer.

For data logging, a custom-built hardware device was used to measure the supercapacitor voltage. The data samples were stored and visualized using the Home Assistant environment.

Real-World Test – First Prototype

Nelectra • 41 minutes ago • 0 comments

In the first real-world test, the system was connected to a 9 V DC latching solenoid valve (Rain Bird) and a DHT11 temperature and humidity sensor.

The node communicated with a receiver (XIAO ESP32-C3) every 10 minutes. In addition, the solenoid was actuated in both directions every 30 minutes, with each switching event lasting approximately 1 second.

This setup was used to evaluate the energy of real actuator operation under typical outdoor IoT conditions.

The measurements show that each solenoid actuation caused the supercapacitor voltage to drop by approximately 11 mV, corresponding to an energy consumption of about 550 mJ at ~4.5 V.

These results confirm that even high-power mechanical switching can be supported within a supercapacitor-based, battery-free energy budget when duty cycles are properly managed.

This makes it suitable for applications such as remote irrigation systems where latching valves are used to minimize energy consumption.

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