Energy Harvesting for Embedded and IoT Devices

What is Energy Harvesting?

Energy harvesting (also called energy scavenging) is the process of capturing small amounts of energy from the environment and converting it into electrical energy to power embedded devices. Instead of relying solely on batteries, the device generates its own power from ambient sources like light, heat, vibration, or radio waves.

The goal is not to replace batteries entirely (though that is sometimes possible) but to extend battery life significantly or eliminate the need for battery replacement in remote, hard-to-reach devices.

Energy Harvesting Sources

1. Solar (Photovoltaic)

Solar cells convert light into electricity. This is the most mature and widely used energy harvesting technology.

Best for: Outdoor sensors, weather stations, agricultural monitors, solar-powered trail cameras.

Design considerations:

• Outdoor solar panels can easily power most IoT devices with a rechargeable battery as backup for nighttime and cloudy days
• Indoor solar harvesting generates very little power, only suitable for ultra-low-power devices (BLE beacons, e-paper displays)
• Use a solar charge controller IC (like BQ25570 or SPV1050) to manage charging

Typical outdoor solar IoT system:

  [Solar Panel 5V/200mA] ──── [Charge Controller] ──── [LiPo Battery]
                                                            |
                                                     [Voltage Regulator]
                                                            |
                                                       [MCU + Sensor]

2. Thermoelectric (TEG – Temperature Gradient)

Thermoelectric generators (TEGs) convert temperature differences into electricity using the Seebeck effect. A TEG placed between a hot surface and ambient air generates a small voltage.

Best for: Industrial monitoring on hot pipes, wearable devices powered by body heat, engine monitoring.

Challenge: TEGs produce very low voltage (millivolts). You need a boost converter with ultra-low startup voltage (like the LTC3108 or BQ25570) to step up to a usable level.

3. Vibration / Piezoelectric

Piezoelectric materials generate a small voltage when mechanically deformed (bent, compressed, or vibrated). Vibration energy is common in industrial environments (motors, pumps, vehicles).

Best for: Vibration sensors on industrial equipment, tire pressure monitors, structural health monitoring.

Challenge: Output is AC (alternating), so you need a rectifier and energy storage. Power output depends heavily on matching the harvester’s resonant frequency with the vibration frequency.

4. RF (Radio Frequency) Harvesting

RF energy harvesting captures energy from ambient radio waves (WiFi, cellular, TV broadcast signals) or from a dedicated RF transmitter.

Best for: RFID tags, NFC-powered sensors, wireless charging for small devices.

Challenge: Ambient RF energy is extremely low. Practical RF harvesting usually requires a dedicated transmitter nearby (like NFC/RFID readers).

Energy Storage for Harvesting Systems

Harvested energy is often intermittent and insufficient for continuous operation. You need energy storage to buffer the harvested energy:

Rechargeable Battery

LiPo batteries store large amounts of energy and can power the device when harvesting is unavailable (nighttime for solar, no vibration during downtime).

Supercapacitor

Supercapacitors (also called ultracapacitors) store less energy than batteries but can be charged/discharged millions of times without degradation. They handle fast charge-discharge cycles well.

Many designs use both: a supercapacitor for short-term buffering and burst current delivery, with a small LiPo for longer-term storage.

System Architecture

A typical energy harvesting system has these building blocks:

  [Energy Source] ──── [Harvester IC] ──── [Energy Storage] ──── [Regulator] ──── [MCU + Load]
  (solar, TEG,         (boost/buck,        (supercap or          (LDO or
   piezo, RF)           MPPT, rectifier)    LiPo battery)         buck)

The harvester IC is critical. It performs:

• Maximum Power Point Tracking (MPPT): Extracts maximum power from solar panels by finding the optimal operating voltage
• Voltage conversion: Steps up or down the harvested voltage to charge the storage element
• Charge management: Protects the battery from overcharging

Popular energy harvesting ICs:

Practical Example: Solar-Powered Weather Station

Components:
  - 6V/1W solar panel
  - BQ25570 harvester IC with MPPT
  - 500mAh LiPo battery
  - ESP32 microcontroller
  - BME280 temperature/humidity/pressure sensor
  - LoRa module for long-range data transmission

Operation:
  1. Solar panel charges LiPo through BQ25570 during daylight
  2. ESP32 wakes from deep sleep every 15 minutes
  3. Reads BME280 sensor (takes ~50ms)
  4. Sends data via LoRa (takes ~200ms at 100mA)
  5. Returns to deep sleep (5uA)
  6. LiPo sustains operation through nighttime and cloudy periods

Power Budget:
  Solar input (average, 6 hours sun): ~100mA x 6h = 600 mAh/day
  Device consumption (average 40uA): ~1 mAh/day
  Result: Solar generates 600x more than consumed. Battery mostly stays full.

When is Energy Harvesting Practical?

Good fit:

• Device average power is under 1mW (most of the time sleeping)
• Energy source is reliable (outdoor solar, constant vibration, hot surface)
• Replacing batteries is expensive or impractical (remote locations, sealed enclosures)
• Long deployment lifetime is required (5-20 years)

Not a good fit:

• Device needs continuous high power (WiFi streaming, displays always on)
• Harvesting source is unreliable or too weak
• Adding the harvesting hardware costs more than periodic battery replacement

Summary

Energy harvesting extends or eliminates battery dependence for embedded devices by capturing ambient energy from light, heat, vibration, or radio waves. Solar is the most practical and widely used source. The key to successful energy harvesting is designing an ultra-low-power device first: if your device sleeps most of the time and draws microamps on average, even a small solar cell or TEG can keep it running indefinitely. The combination of aggressive sleep modes, efficient duty cycling, and energy harvesting makes truly maintenance-free IoT devices possible.

Vivek Bhageria

Vivek Bhageria — Lead Firmware R&D Engineer, 12+ years. Ex-Bosch (automotive powertrain), MusicTribe (real-time audio), medical devices. M.Tech BITS Pilani. I write at NerdyElectronics — practical, register-level embedded systems for engineers who want to understand what’s actually happening under the hood.

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