Meshtastic Project

Solar Power Options for Meshtastic Nodes

Power Consumption Basics

Average Power Requirements

  • ESP32-based devices: ~0.1W (100mW) on average without Bluetooth, screen, or GPS
  • nRF52-based devices: Significantly lower power consumption than ESP32
  • Daily consumption: 100-1000 mAh per day (average ~400 mAh)
  • Power consumption varies based on duty cycle (percentage of time spent transmitting)

Measuring Power Consumption

  • Power is measured in watt-hours (Wh) or milliwatt-hours (mWh)
  • Formula: Volts × Amps = Watts
  • Example: 5V × 50mA = 250mW
  • For accurate measurements, test for 2-6 hours under realistic conditions
  • Consider background network activity in measurements

Battery Sizing

Capacity Requirements

  • Minimum recommended: 3000 mAh
  • Ideal for solar applications: 5000+ mAh
  • For 30-day operation without solar: ~10,000-15,000 mAh

Battery Types

  • 18650 Li-ion cells: Common, affordable, 2500-3500 mAh capacity
  • LiPo batteries: Lighter, flexible form factor
  • Both perform well in most climates (even cold temperatures)

Battery Protection

  • Over-discharge protection is critical for Li-ion/LiPo batteries
  • Many 18650 cells don't have built-in protection
  • Options:
    • Battery packs with built-in protection circuits
    • Dedicated battery protection modules
    • Charge controllers with low-voltage cutoff

Solar Panel Sizing

General Guidelines

  • Rule of thumb: 10Wp (Watt peak) solar panel for every 10Wh of battery capacity
  • Requires approximately 3 hours of full sunshine for a complete recharge
  • Example: 2500mAh (9Wh) battery needs ~10W solar panel

Practical Considerations

  • Oversize panels for winter/cloudy conditions
  • Panel angle matters for optimal solar collection
  • Maximum charging current is limited by battery (typically 1A for 18650 cells)
  • Maximum charging power for a typical 18650 cell: ~4.2W (1A × 4.2V)

Charge Controllers

Types of Controllers

  1. CN3791: True MPPT controller

    • Input voltage up to 28V
    • Charge current up to 4A
    • Trickle charges batteries below 66% capacity
    • Most efficient option

  2. CN3163: Pseudo-MPPT controller

    • Maintains minimum 4.4V solar input
    • Adjusts charge rate based on temperature
    • Good middle-ground option

  3. TP4056: Basic Li-ion charger

    • No special solar functionality
    • Common in low-cost solar chargers
    • Less efficient for solar applications

Voltage Regulators

  • 3.3V regulators needed for microcontrollers
  • Low dropout voltage important (ability to work with lower battery voltage)
  • Example: CE6260 has 0.12V dropout at 100mA (stops working at battery voltage below 3.42V)

Commercial Solar Solutions for Meshtastic

Integrated Solar Cases

  1. 4W Solar Panel with 18650 Battery Case

    • Integrated case for six 18650 cells
    • Built-in charging circuit
    • Provides space for Meshtastic hardware
    • Winter charging power limited to ~1W

  2. Solar-Powered Enclosures

    • Various commercial options with integrated panels
    • Often include mounting hardware
    • Weather-resistant designs

Complete Solar Meshtastic Nodes

  1. LowMesh Pocket-S

    • Built-in solar panel (6.6v/0.8W)
    • 2000mAh LiPo battery
    • MPPT-style solar charging
    • Portable design

  2. Atlavox Beacon

    • 5W ETFE Solar Panel
    • 5,000mAh LiPo battery
    • Multiple mounting options
    • Weatherproof enclosure

DIY Solar Configurations

Austin Mesh Recommended Setup (Version 5.0)

  • 12W solar panel connected to battery via USB
  • Voltaic Systems V25 battery with built-in charge controller
  • RAK Meshtastic Kit
  • Battery handles solar charging and provides overdischarge protection
  • Automatic reboot when sufficiently recharged

Lessons Learned from Field Deployments

  1. Don't rely on development board's built-in solar/battery management
  2. Bigger solar panels are better (10W+ recommended)
  3. Larger batteries provide more buffer (5000+ mAh)
  4. Fiberglass antennas are most durable for outdoor use
  5. Shade the battery compartment to prevent heat damage
  6. Disable unnecessary features (GPS, screen) to save power
  7. Proper sealing and drainage are essential for outdoor nodes

Environmental Considerations

Hot Climates

  • Heat can damage batteries and reduce lifespan
  • Shade battery compartments
  • Ensure adequate ventilation

Cold Climates

  • Battery capacity is reduced but still functional
  • nRF52-based boards perform better than ESP32
  • Charging creates heat which helps in cold environments

Coastal/Humid Environments

  • Use conformal coating on electronics
  • Ensure proper sealing and drainage
  • Consider silica gel packets inside enclosures