Author: Zhao Xiaofei, Original
Passive IoT is projected to reach hundred-billion-scale connections over the next decade. Its most defining characteristic is enabling IoT devices and sensors to operate without batteries, achieving self-powering. Ambient energy harvesting technology is emerging as a transformative solution, allowing devices to autonomously harvest energy from their surroundings. By collecting external energy sources such as RF signals, temperature gradients, mechanical vibrations, and ambient light, it supplies the necessary power to the devices. This ensures that IoT nodes can operate for years or even potentially indefinitely, entirely eliminating the need for batteries.
For engineers, energy harvesting represents the convergence of ultra-low-power electronics, advanced materials, Power Management ICs (PMICs), and wireless communication technologies. As ultra-low-power electronics steadily mature, battery-less devices are poised to become standard in scenarios such as Industry 4.0, smart cities, medical wearables, and environmental monitoring systems.
Diverse Energy Harvesting Technologies Support Passive IoT
Energy harvesting technology is shifting IoT design from a "battery-first" paradigm to ultra-low-power, low-maintenance nodes that harvest energy from their surroundings. In practice, this means converting ambient light, RF energy, temperature gradients, vibrations, or motion into usable electrical power, which is then stored and regulated for use by sensors, MCUs (Microcontroller Units), and radio burst transmissions. The result is a class of devices that can operate in locations where wiring is prohibitively expensive or battery replacement is impractical.
Vibration-Based Energy Harvesting: Industrial machinery generates continuous vibrations, and piezoelectric materials convert this mechanical energy into electrical power—typically 10-100 µW/cm³, which is sufficient to support intermittent sensor transmissions. For example, sensors mounted on conveyor belt motors can monitor temperature and runtime without batteries, waking up only when vibrations are present. Several industrial IoT solution providers have already delivered similar deployments.
Thermoelectric (Heat-Based) Energy Harvesting: Thermoelectric generators utilize temperature gradients to generate voltage. A temperature difference of just 5°C can produce usable power, while industrial applications such as furnaces, boilers, and exhaust stacks typically provide temperature gradients of 20-50°C. Although the energy conversion efficiency of this method is relatively low, the energy is free and continuous.
Light-Based (Photovoltaic) Energy Harvesting: This is the most mature and widely deployed method. Outdoor solar energy provides power ranging from milliwatts to watts per square centimeter, which is sufficient to support the continuous operation of certain devices. Indoor photovoltaics have traditionally achieved efficiencies of 15-25% under office lighting, while in 2026, commercial perovskite cells have reached 32-38%. For instance, warehouse sensors operating under indoor lighting can transmit readings hourly, indefinitely.
RF-Based Energy Harvesting: Capturing ambient radio waves (Wi-Fi, cellular networks, dedicated transmitters) can generate a small amount of energy. Although the power levels in this method are extremely low (microwatt range), it is viable for ultra-low-power devices in high-RF environments.
Kinetic (Motion/Flow-Based) Energy Harvesting: This method goes beyond vibrations. In rotating shafts, fluid flow in pipes, or even human motion, electromagnetic or triboelectric generators convert this movement into electrical power. For example, some manufacturers have implemented pipe flow monitors powered by small turbines integrated into the pipelines.
For engineers working in energy harvesting, the critical shift is not just the harvester itself, but the entire power chain. A successful energy harvesting design requires the harvester, energy storage components, cold-start circuits, and PMICs to work in synergy. Vendors also emphasize Maximum Power Point Tracking (MPPT) and ultra-low quiescent current, as the harvested power is typically measured in microwatts or low milliwatts, rather than watts.
The most promising ambient energy harvesting technologies are highly matched to their actual deployment environments. RF harvesting is attractive for low-power tags and low-duty-cycle nodes because it can convert broadcast energy into a stable power source, even though the received power is usually small and varies with distance. Thermal energy harvesting utilizes temperature differences, including body heat or industrial thermal gradients, making it ideal for wearables and sensors located near machinery. Vibration and piezoelectric harvesting are natural choices for motors, pumps, rotating equipment, and transported assets.
Breakthroughs Needed in Multiple Areas of Energy Harvesting Technology
Energy harvesting technology also faces numerous engineering challenges, including power budgeting, energy storage, and efficiency.
Power Requirements vs. Harvesting Capability: In practice, many scenario designs are fundamentally unsuitable for energy harvesting because they consume tens of milliamperes or more under normal operating conditions. While some scenarios are viable with solar arrays, in many cases, size or location constraints do not allow for sufficiently large panels. Other harvesting forms, such as piezoelectric, RF, and thermoelectric, are unlikely to power such devices. Therefore, the first question is whether the application of energy harvesting technology is feasible. If a customer's product draws microamp-level current most of the time, with transmission pulses in the milliamp range, it could be an excellent choice.
Energy Storage: Energy harvesting does not eliminate the need for energy storage in most cases. For example, if a customer uses a photovoltaic power source but needs to operate in the dark, energy must be stored when light is available. In this scenario, the storage and photovoltaic sources must be sized not only to provide enough energy to power the device during the day but also to have sufficient margin to last through the night. Storage typically means capacitors or even batteries; the former is suitable for ultra-low-power devices, while the latter is for higher-power devices. Both require designing the rated capacity and size not just for the initial product lifespan, which often implies overdesigning.
Efficiency and Energy Conversion: Energy conversion efficiency remains a critical requirement for all harvesting technologies. Current thermoelectric generators typically have an efficiency of only 5-10%, while indoor photovoltaic cells can achieve 15-25% efficiency under optimal conditions. These limitations mean that harvesting systems must be meticulously designed to maximize energy capture and minimize losses. Here, the Power Management IC (PMIC) plays a core role in optimizing efficiency, as it must handle irregular and unpredictable energy inputs while maintaining a stable power output. Advanced PMICs specifically designed for energy harvesting applications have emerged, integrating features such as Maximum Power Point Tracking (MPPT) and ultra-low-power DC-DC conversion to extract the maximum available energy from ambient sources.
Environmental Variability: Industrial environments, in particular, are rarely stable, posing a challenge for harvesting systems that rely on consistent ambient energy sources. Vibration-based systems may encounter intermittently operating machinery, while light-based systems must cope with varying illumination conditions. This variability necessitates robust energy storage solutions, such as supercapacitors or small rechargeable batteries, to ensure continuous device operation when harvested energy is unavailable.
Ultra-Low-Power Design: Creating truly self-powered IoT devices requires a fundamental shift in design methodology. Every aspect of the device must be optimized for ultra-low power consumption, including microcontrollers that support multiple deep sleep modes, sensors with low sampling power and fast wake-up times, communication protocols optimized for minimal transmission power, and firmware designed to maximize sleep time while maintaining functionality. In many cases, this means rethinking data acquisition and transmission strategies. Instead of continuous monitoring, energy harvesting devices typically adopt event-driven sensing or scheduled wake-up modes to save energy while still providing valuable insights.
Size and Integration Constraints: Another practical challenge is the physical issue of integrating energy harvesting components into IoT devices. Harvesting mechanisms often require specific positioning or orientation to maximize energy capture; for example, vibration harvesters need to be aligned with the primary vibration axis, while photovoltaic cells need exposure to light sources. These requirements may conflict with other design constraints, especially for retrofit applications in existing equipment. Addressing these issues requires a holistic device design approach that considers not only the energy harvesting mechanism but also the entire power architecture from generation to storage to consumption. Successful implementation requires collaboration among mechanical, electronic, and software engineers to create truly optimized solutions that can operate reliably in industrial environments for years without maintenance.
Looking ahead, the convergence of energy harvesting, ultra-low-power electronics, AI (Artificial Intelligence)-enabled edge processing, and advanced semiconductor materials is creating a new class of passive IoT devices. Many pioneers are already developing systems capable of running continuously on harvested microwatt power while performing local machine learning inference. As device power consumption continues to drop, the vision of truly maintenance-free passive IoT networks is becoming increasingly realistic. In this process, energy harvesting micropower technology is rapidly becoming a foundational enabling technology for next-generation IoT systems.
Passive IoT nodes utilizing energy harvesting technology will first win out in asset tracking, smart buildings, wearables, industrial condition monitoring, shelf labels, and distributed sensing. This is because installation and service costs dominate in these areas, which is precisely the market segment that energy harvesting is poised to fill.