Power Budget Audit: Standby Math & Seasonal Sun Hours
Guessing kills batteries. Auditing buys freedom.
1) List Every Always-On Load
| Device | Standby W | Hrs/day | Wh/day |
|---|---|---|---|
| Smart Lock | 0.2–0.5 | 24 | 4.8–12 |
| Door Sensor | 0.05–0.2 | 24 | 1.2–4.8 |
| Router (if used) | 2–6 | 24 | 48–144 |
Add 15–25% conversion loss for bucks/controllers.
2) Seasonal Sun Hours (Peak-Sun Reality)
- Summer: 4–6 h/day
- Shoulder: 3–4 h/day
- Winter: 1.5–3 h/day (snow, angle, clouds)
Panel sizing: Panel W ≥ Wh/day ÷ (sun hours × 0.75). Design to winter.
3) Autonomy Target
Battery Wh ≥ Wh/day × days of autonomy (e.g., 7). Convert to Ah at system voltage.
4) Kill or Schedule
- Switch routers/cameras off at night.
- Use low-idle controllers and efficient bucks.
- Shorten cable runs to cut drop and waste.
5) Verify With a Meter
Measure DC current at the battery with everything "off". That's your baseline. Re-measure after changes. Numbers or it didn't happen.
A 10 W panel can power a lock forever — if the rest of your "tiny crew" behaves.
Related Reading
- Solar-Powered Smart Lock Kit — Panel sizing and controller selection.
- Battery Chemistry for Off-Grid Smart Locks — Battery capacity planning.
- Extreme Cold Starts — Winter power budget considerations.