How to Choose a Solar Repeater for Meshtastic or MeshCore?

What is Mesh Solar Repeater?also known as a Solar Node, Meshtastic Repeater Node, or MeshCore Repeater Node, is an off-grid, autonomous LoRa mesh relay node designed to extend network coverage for Meshtastic and MeshCore systems. Integrated with a 4-in-1 solar power kit (solar panel, charge controller, battery, and LoRa module), this device is ideal for fixed high-mount deployments such as rooftops, poles, or towers. It enables 24/7/365 operation, even during low sunlight or winter months, by using solar energy for power. The solar repeater effectively forwards LoRa packets between network nodes, helping to eliminate range gaps and ensuring continuous operation without relying on grid power.

When selecting a solar repeater for your Meshtastic or MeshCore network, it’s essential to consider the following four key factors to ensure you choose the right device for your specific needs.

1) Solar Panel Power:

The solar panel power is a critical factor. In general, the higher the power of the solar panel, the faster the charging speed. However, panel power is not always directly proportional to its physical size, and the conversion efficiency rate must also be considered. Conventional solar panels typically have a conversion efficiency of about 18–21%, but BC solar cells can achieve up to 24% efficiency. Additionally, larger panels may present installation challenges and incur higher costs.

Technical Guidelines for Solar Panel Selection with LoRa Modules:

1. nRF52840 MCU + SX1262 LoRa Chip: The nRF52840 chip is ultra-low power, so a 5W solar panel is sufficient, even in winter.
   
   

2. ESP32 + SX1262 LoRa Chip: A 5W solar panel works well in summer, but power may be depleted in winter, especially with high-frequency use.
   
   

3. ESP32 + SX1262 LoRa Chip + GPS Module: A 7W solar panel is required, with a recommendation of a 10W solar panel. This is due to the high power consumption of the ESP32 WiFi module and the GPS module.
   
   

Key Recommendation: Integrating a GPS module into a solar-powered LoRa repeater is not recommended due to high power demands.

2) Controller:

Why Does a Solar System Need a Controller?

When choosing a solar system for your Meshtastic or MeshCore network, it’s essential to include a built-in controller. Without a controller, the output voltage from the solar system can become unstable, fluctuating with changes in sunlight intensity. This instability could potentially damage the LoRa module. Therefore, the controller is crucial for maintaining a steady and reliable power supply.

3.7V LoRa Module Voltage Compatibility:

Most LoRa modules support both 3.7V and 5V inputs. The controller should be capable of outputting 3.7V directly from the battery, allowing the LoRa module to accurately read the battery level and display it on the Meshtastic or MeshCore app.

Does the Controller Need MPPT?

Not necessarily. We tested various MPPT chips with different solar panel sizes: 5W, 10W, and 20W. Our results showed that the MPPT controller improves efficiency by 15-23% when working with a 20W solar panel. However, there was no significant improvement in efficiency when using 5W and 10W solar panels. Therefore, an MPPT controller is not necessary for panels less than 20W.

(Contact us for detailed testing results)

3) Battery: What Battery Capacity Do You Need?

The battery capacity required for your LoRa module depends on the specific module used.

• For an ESP32 WiFi BLE MCU LoRa module, we recommend a 10,000mAh battery (4 x 18650 lithium batteries).
  
  

• For an nRF52840 BLE MCU LoRa module, a 5,500mAh to 6,000mAh battery (2 x 18650 lithium batteries) is sufficient.
  
  

4) LoRa Module: Choosing the Best LoRa Module for Meshtastic/MeshCore

Heltec, RAKwireless, Seeedstudio, LilyGo, and Elecrow are the original contributors to the Meshtastic open-source project and were among the first to design and develop Meshtastic-compatible boards.

The most popular LoRa modules with ESP32 MCU + SX1262 LoRa chip include the Heltec ESP32 V3, Heltec ESP32 S3 V4, LilyGo T3, T3S3, and T Beam series. The Heltec ESP32 V3 is particularly noted for its simplicity, low cost (around $10-$15), and high cost-effectiveness, making it an excellent choice for Meshtastic beginners or starter kits.

The nRF52840 is a low-power Bluetooth chip. When paired with the SX1262 LoRa chip, it forms an ideal combination, especially for mesh network products and solar-powered nodes. RAKWireless produces LoRa modules such as the RAK19007+4631 and RAK19003+4631, which are highly favored for their outstanding low power consumption. Similarly, Seeedstudio's XIAO nRF52840 + SX1262 offers a compact design that is perfect for integration into other products.

In Summary:

• ESP32 + SX1262 LoRa modules consume approximately 150mAh, which is higher in power consumption but more affordable.
  
  

• nRF52840 + SX1262 LoRa modules consume approximately 20mAh, making them more power-efficient, although they come at a higher price.