Solar Sizing Guide

A correctly sized solar system keeps your repeater running indefinitely with no maintenance - an undersized system fails within days during cloudy weather. 

 The two goals of solar sizing 
 
 Enough panel to fully recharge the battery on a typical sunny day 
 Enough battery to run through several consecutive cloudy days (autonomy period) 
 

 Step 1: Calculate daily energy consumption 
 Use the power consumption tables on the previous page. For a typical optimized nRF52 repeater (6 mA average): 
 Daily consumption = 6 mA × 24 h = 144 mAh = 0.144 Ah
At 3.7V: 0.144 Ah × 3.7 V = 0.53 Wh/day 
 For an ESP32 repeater at 40 mA: 40 × 24 = 960 mAh = 3.55 Wh/day 

 Step 2: Size the battery 
 Rule of thumb: target 5 days of autonomy (no sun). Use 80% usable depth-of-discharge for LiFePO4: 
 Battery (Ah) = (daily consumption × 5 days) / 0.8

nRF52 example: (0.144 Ah × 5) / 0.8 = 0.9 Ah minimum → use 5 - 10 Ah for margin
ESP32 example: (0.96 Ah × 5) / 0.8 = 6.0 Ah minimum → use 10 - 20 Ah
 

 Step 3: Size the solar panel 
 Assume 4 peak sun hours per day (conservative for most of North America year-round). Add 25% for charge controller inefficiency and panel degradation: 
 Panel (W) = (daily Wh × 1.25) / peak sun hours

nRF52 example: (0.53 Wh × 1.25) / 4 = 0.17W minimum → 1 - 3W panel is more than sufficient
ESP32 example: (3.55 Wh × 1.25) / 4 = 1.1W minimum → 5 - 10W panel recommended 

 Typical RegionMesh community build: $180 - $300 
 This is the build specification widely used by community mesh networks including RegionMesh and CascadiaMesh : 

 
 Component Spec Cost 
 
 Solar panel 5W, south-facing, 30 - 40° tilt (match your latitude) $15 - 25 
 Charge controller 5A MPPT (e.g. Victron 75/5 or generic CN3791) $15 - 30 
 Battery LiFePO4 10 Ah (4S, 12.8V) or 3.2V single cell 10 Ah $25 - 60 
 Radio board RAK4631 or Heltec V4 or T-Echo $18 - 75 
 Enclosure IP65 ABS junction box, 200×120×75mm $10 - 20 
 Antenna 5 dBi fiberglass, N-female mount $15 - 25 
 Misc Cable glands, silicone, fuse, wiring $10 - 20 
 Total $108 - $255 
 
 

 Panel mounting orientation 
 
 Azimuth: Face south (in North America). A deviation of up to 30° east or west reduces output by only ~5%. 
 Tilt angle: Set to your latitude for best year-round average. Steeper tilt (latitude + 15°) optimizes for winter; shallower (latitude − 15°) for summer. 
 Avoid shading: Even partial shading of one cell can reduce output of the entire panel significantly. Use terrain and shadow analysis before finalizing mount position. 
 

 Charge controller: MPPT vs PWM 
 Always use MPPT for solar-powered mesh nodes: 
 
 MPPT controllers extract up to 30% more power from the panel under real-world conditions 
 On small systems (3 - 10W panels), this can be the difference between running indefinitely and failing in winter 
 PWM is only acceptable for large panels where the extra efficiency isn't needed to meet the load