1615  Energy Harvesting Cycle Animation

Interactive Visualization of IoT Energy Harvesting Systems

animation
energy-harvesting
power-management
design-strategies

1615.1 IoT Energy Harvesting System

This interactive animation demonstrates how IoT devices can operate indefinitely by harvesting energy from environmental sources. The system shows the complete energy flow: harvest from source, store in capacitor/battery, regulate voltage, and power the load.

1615.2 Understanding Energy Harvesting

NoteThe Promise of Energy Harvesting

Energy harvesting enables IoT devices to operate indefinitely without battery replacement by capturing ambient energy from the environment. This is crucial for:

  • Remote deployments where battery replacement is impractical
  • Sustainable IoT reducing battery waste
  • Maintenance-free sensor networks
  • Perpetual operation for monitoring applications

1615.3 Energy Harvesting Cycle

The energy harvesting cycle consists of four key stages:

%% fig-alt: Flow diagram showing the four stages of energy harvesting: environmental energy source feeds into harvester/converter, which charges storage element, then voltage regulator provides stable power to IoT load.
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flowchart LR
    subgraph Source["1. Energy Source"]
        S1[Solar]
        S2[Vibration]
        S3[Thermal]
        S4[RF]
    end

    subgraph Harvest["2. Harvester"]
        H1[DC-DC Converter]
        H2[MPPT Controller]
    end

    subgraph Store["3. Storage"]
        ST1[Supercapacitor]
        ST2[Li-ion Battery]
    end

    subgraph Regulate["4. Regulator"]
        R1[LDO/Buck]
        R2[3.3V Output]
    end

    subgraph Load["5. IoT Device"]
        L1[MCU]
        L2[Sensors]
        L3[Radio]
    end

    Source --> Harvest
    Harvest --> Store
    Store --> Regulate
    Regulate --> Load


%% fig-alt: Decision tree for selecting energy harvesting source based on deployment environment, showing solar for outdoor lit areas, vibration for machinery, thermal for body-worn or industrial heat, and RF for indoor range-limited scenarios.
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flowchart TD
    START[Select Energy Source] --> Q1{Outdoor<br/>Deployment?}
    Q1 -->|Yes| Q2{Sunlight<br/>Available?}
    Q2 -->|Yes| SOLAR[Solar Panel<br/>10-100 mW/cm2<br/>Best for outdoor]
    Q2 -->|No| Q3{Vibration<br/>Present?}

    Q1 -->|No| Q4{Body-worn<br/>Device?}
    Q4 -->|Yes| THERM[Thermoelectric<br/>Body heat ~30 mW<br/>Wearables]
    Q4 -->|No| Q5{Near RF<br/>Source?}

    Q3 -->|Yes| VIB[Piezoelectric<br/>Machinery vibration<br/>0.1-10 mW]
    Q3 -->|No| THERM2[Thermal<br/>Industrial heat]

    Q5 -->|Yes| RF[RF Harvesting<br/>RFID/Wi-Fi<br/>0.001-1 mW]
    Q5 -->|No| HYBRID[Hybrid System<br/>Multiple sources<br/>Reliability]

    style START fill:#2C3E50,stroke:#16A085,stroke-width:2px,color:#fff
    style SOLAR fill:#F1C40F,stroke:#2C3E50,stroke-width:2px,color:#000
    style VIB fill:#9B59B6,stroke:#2C3E50,stroke-width:2px,color:#fff
    style THERM fill:#E74C3C,stroke:#2C3E50,stroke-width:2px,color:#fff
    style THERM2 fill:#E74C3C,stroke:#2C3E50,stroke-width:2px,color:#fff
    style RF fill:#3498DB,stroke:#2C3E50,stroke-width:2px,color:#fff
    style HYBRID fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff

This decision tree guides energy source selection based on deployment environment. Solar provides highest power density for outdoor applications. Vibration harvesting suits machinery environments. Thermal harvesting works for body-worn devices or industrial heat sources. RF harvesting enables indoor applications near transmitters but provides very low power.

1615.4 Energy Sources Comparison

Comparison of Energy Harvesting Sources
Source Power Density Typical Power Advantages Challenges
Solar 10-100 mW/cm2 1-100 mW High power, predictable Light dependent, large area
Vibration 0.1-1 mW/cm2 0.1-10 mW Always available (machinery) Motion dependent, resonance
Thermal 10-50 uW/cm2 0.1-30 mW Body heat, industrial Low efficiency, needs gradient
RF 0.1-1 uW/cm2 0.001-1 mW Works indoors Very low power, distance

1615.5 Energy Balance Equation

For sustainable operation, the energy balance must be positive or zero:

\[E_{harvested} \geq E_{consumed} + E_{storage\_loss}\]

Average power requirement:

\[P_{avg} = \frac{E_{active} \times t_{active} + E_{sleep} \times t_{sleep}}{t_{total}}\]

Where:

  • \(E_{harvested}\) = Energy captured from environment
  • \(E_{consumed}\) = Energy used by the IoT device
  • \(E_{active}\) = Power during active mode
  • \(t_{active}\) = Time in active mode
  • \(E_{sleep}\) = Power during sleep mode
  • \(t_{sleep}\) = Time in sleep mode

1615.6 Storage Element Selection

%% fig-alt: Decision tree for selecting energy storage showing supercapacitor preferred for high cycle life and fast charging, battery preferred for higher energy density and longer duration storage.
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flowchart TD
    A[Storage Selection] --> B{High Cycle Life<br>Needed?}
    B -->|Yes| C{Fast Charge<br>Required?}
    B -->|No| D{High Energy<br>Density?}

    C -->|Yes| E[Supercapacitor]
    C -->|No| F[Hybrid System]

    D -->|Yes| G[Li-ion Battery]
    D -->|No| H[Thin-film Battery]

    E --> I["100k+ cycles<br>Seconds to charge<br>Lower energy density"]
    G --> J["500-1000 cycles<br>Hours to charge<br>Higher energy density"]
    F --> K["Best of both<br>Supercap + Battery"]
    H --> L["Flexible form factor<br>Lower capacity"]

1615.7 Design Guidelines

TipEnergy Harvesting Best Practices
  1. Oversize the harvester by 2-3x expected load for margin
  2. Use MPPT (Maximum Power Point Tracking) for solar to maximize efficiency
  3. Implement duty cycling to reduce average power consumption
  4. Size storage for expected periods without harvesting (night, calm weather)
  5. Add brownout protection to gracefully handle energy depletion
  6. Monitor energy budget in firmware to adapt behavior
WarningCommon Pitfalls
  • Undersized storage: Not enough buffer for consumption spikes
  • Ignoring leakage: Storage elements lose charge over time
  • No energy awareness: Software doesn’t adapt to energy availability
  • Wrong harvester for environment: Using solar indoors, RF in rural areas

1615.8 What’s Next

Now that you understand energy harvesting systems, explore these related topics:

Animation created for the IoT Class Textbook - ENERGY-001