Solar Relay v2
An always-on repeater you can bolt to a fence post, rooftop, or grain bin and forget about. It runs entirely on a small solar panel and a single 18650 cell, and it's sized to ride out a cloudy week without dropping off the mesh. This is the workhorse that fills the gaps between bigger gateways.
Prices below are ballpark examples and move around a lot by vendor and season. Treat them as a starting point and check current pricing where you actually buy. Buy wherever you like — nothing here is sponsored.
Bill of materials
| Item | Qty | ~Cost | Notes |
|---|---|---|---|
| Heltec WiFi LoRa 32 V3 | 1 | $18 | ESP32-S3 + SX1262 |
| 915 MHz antenna (3–5 dBi) | 1 | $8 | SMA, weatherproof base |
| 6 W solar panel | 1 | $14 | 5–6 V output |
| TP4056 / solar charge board | 1 | $3 | with protection |
| 18650 cell + holder | 1 | $7 | quality cell, not a no-name |
| Weatherproof enclosure | 1 | $10 | IP65 or printed (see manual) |
| Cable glands, wire, hardware | — | $8 | gland for the antenna lead |
| Approx. total | 14 | ~$68 | per node |
Power budget (why it survives the clouds)
A relay sips power because it mostly listens and forwards. Budget for the worst case — several gray days with little charging — and size the battery so the node keeps running while the panel barely keeps up. The full math (panel watts, daily charge, average draw, days of autonomy) lives in the solar power budget manual; this build targets roughly a week of autonomy on a single healthy 18650.
Assembly
- Flash first. Get Meshtastic on the Heltec before it goes in the box — see Flash a Heltec V3. Set the role to
ROUTERfor a dedicated relay. - Wire the power chain. Solar panel → charge board (IN) → 18650 (BAT) → board (OUT) → Heltec 5V/USB input. Double-check polarity before connecting the cell.
- Mount the antenna. Run the antenna through a cable gland so the seal stays intact. Keep the lead short and the antenna vertical and as high as you can.
- Seal the box. Panel and antenna outside, electronics inside, gasket seated. Add a little desiccant.
- Aim the panel. Face it toward the equator (south, in the Midwest) at a steep-ish tilt so snow sheds and low winter sun still hits it.
- Soak test. Leave it on the bench for 24–48h and watch the battery voltage recover each day before you climb anything.
Height beats power. The radio horizon grows with the square root of antenna height, so a relay 5 m up has roughly a 9 km horizon against about 5 km for one sitting on a desk — see the field notes on why height beats wattage.