Solar-Powered Smart Lock Kit: Panel, Controller, Buck — Done Right

Goal: 24/7 reliability with a panel so small it's almost rude.

1) Load Budget (Reality First)

Standby: 0.2–0.5 W × 24 h = 4.8–12 Wh/day
Actuation: motor bursts ≪ 0.1 Wh/day (usually negligible)
Converter loss: add ~15–25% buffer

Design target: 8–12 Wh/day total for most locks.

2) Panel Sizing (Peak-Sun Math)

Panel W ≥ Wh/day ÷ (sun hours × derate). For 8 Wh/day, 4.0 sun hours, 0.75 derate → 8 ÷ (4×0.75) ≈ 2.7 W. Use a 10–20 W panel to cover bad weather + winter.

3) Battery & Controller

Battery: 12 V sealed lead-acid or small LiFePO₄ (3–8 Ah). Capacity target: 7 days autonomy → ~8 Wh/day × 7 ≈ 56 Wh → ~4.7 Ah @ 12 V (round up).
Charge controller: PWM is fine at this scale; MPPT is nice-to-have in winter.

4) Buck Converter (12 → 5 V)

Place the buck near the lock to reduce drop; set output to 5.1 V.
Ferrules on terminals, heatshrink on exposed leads, and strain relief.

5) Protection & Wiring

Fuse at battery positive (1 A slow-blow) within 20 cm.
Inline fuse for the load side (0.5–1 A).
Drip loops on all exterior runs; IP67 glands; neutral-cure silicone.

6) Mounting & Angle

South-facing, tilt ≈ your latitude (seasonal tweak optional). Keep panel shaded-area-free; snow slides off better at steeper angles.

Tiny panel + honest math = set-and-forget power. Use the Energy Calculator with your sun hours.