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

1. Enough panel to fully recharge the battery on a typical sunny day
2. 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 - 5–10 Ah for margin
ESP32 example:  (0.96 Ah × 5) / 0.8 = 6.0 Ah minimum → use 10 - 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 - 1–3W panel is more than sufficient
ESP32 example:  (3.55 Wh × 1.25) / 4 = 1.1W minimum → 5 - 5–10W panel recommended

Typical RegionMesh community build: $180 - 180–$300

This is the build specification widely used by community mesh networks including RegionMesh and CascadiaMesh:CascadiaMesh:

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