Six configurations worked through end to end. Each starts from a measured load, states its assumptions, and ends with array, battery and controller figures. Treat the numbers as design starting points — the site survey always wins.
1. Four-camera CCTV site
| Item | Value |
|---|---|
| Load | 4 cameras × 7 W × 24 h = 672 Wh; NVR 15 W × 24 h = 360 Wh; 4G router 6 W × 24 h = 144 Wh |
| Daily energy | 1,176 Wh/day (+8% conversion = 1,270 Wh) |
| Assumptions | 4.0 worst-month PSH, 3 days autonomy, LiFePO4 |
| Array | 1,270 × 1.25 / (4.0 × 0.70) = 567 Wp → 3 × 200 W or 1 × 550 W + 1 × 100 W |
| Battery | 1,270 × 3 / 0.8 = 4,763 Wh → ~372 Ah at 12.8 V or 93 Ah at 51.2 V |
| Controller | 567 / 24 × 1.25 = 29.5 A → 30-40 A MPPT at 24 V |
| Watch out | IR draws more at night; NVR disk count changes the load; confirm PoE budget |
2. Water level monitoring station
| Item | Value |
|---|---|
| Load | Radar sensor 8 W × 5 min/day = 0.7 Wh; logger 0.5 W × 24 h = 12 Wh; 4G transmit 6 W × 10 min = 1 Wh |
| Daily energy | ~14 Wh/day (round to 20 Wh for design) |
| Assumptions | 4.2 PSH, 6 days autonomy (bridge access), LiFePO4 |
| Array | 20 × 1.25 / (4.2 × 0.70) = 8.5 Wp → practical minimum 50-100 Wp |
| Battery | 20 × 6 / 0.8 = 150 Wh → ~12 Ah at 12.8 V |
| Controller | Very small; 10 A MPPT is ample |
| Watch out | The calculated array is unrealistically small — real installs use 50-100 Wp for early-morning recovery and to survive soiling. The battery’s discharge rating must cover the transmit burst, which is the actual constraint. |
3. Weather station
| Item | Value |
|---|---|
| Load | Logger 0.6 W × 24 = 14 Wh; sensors 1.5 W × 24 = 36 Wh; telemetry 4 W × 1 h = 4 Wh |
| Daily energy | ~54 Wh/day (design at 75 Wh for winter margin) |
| Assumptions | 2.5 worst-month PSH (temperate winter), 7 days autonomy, LiFePO4 with low-temp charge cut-off |
| Array | 75 × 1.25 / (2.5 × 0.70) = 54 Wp → specify 120-150 Wp for snow and rime margin |
| Battery | 75 × 7 / 0.8 = 656 Wh → ~51 Ah at 12.8 V |
| Controller | 10-15 A MPPT |
| Watch out | Winter yield is half the summer value. Cold reduces lead-acid usable capacity sharply; specify low-temperature charge protection for lithium. |
4. GNSS reference station
| Item | Value |
|---|---|
| Load | Receiver 3 W × 24 = 72 Wh; radio 6 W × 0.5 h = 3 Wh |
| Daily energy | ~80 Wh/day |
| Assumptions | 3.8 PSH, 5 days autonomy, LiFePO4 |
| Array | 80 × 1.25 / (3.8 × 0.70) = 38 Wp → specify 100 Wp for ageing and soiling reserve |
| Battery | 80 × 5 / 0.8 = 500 Wh → ~39 Ah at 12.8 V |
| Controller | 10-15 A MPPT |
| Watch out | Uptime matters more than energy. Add coax surge protection at the antenna entry and keep the radio on a local capacitor bank to prevent brownout resets. |
5. 4G telemetry node
| Item | Value |
|---|---|
| Load | Logger 0.4 W × 24 = 10 Wh; modem idle/sleep average 1.2 W × 24 = 29 Wh |
| Daily energy | ~40 Wh/day |
| Assumptions | 4.0 PSH, 4 days autonomy, LiFePO4 |
| Array | 40 × 1.25 / (4.0 × 0.70) = 18 Wp → practical 60-100 Wp |
| Battery | 40 × 4 / 0.8 = 200 Wh → ~16 Ah at 12.8 V, but must sustain 2 A transmit bursts |
| Controller | 10 A MPPT |
| Watch out | Weak signal makes the modem transmit longer at higher power — the energy budget can double. Check coverage at the antenna position before sizing. |
6. Solar irrigation pump (tank-buffered)
| Item | Value |
|---|---|
| Duty | 12 m³/day at 45 m total head |
| Hydraulic energy | 12 × 45 × 2.725 / 1000 = 1.47 kWh/day |
| Electrical energy | 1.47 / 0.55 (wire-to-water efficiency) = 2.68 kWh/day |
| Assumptions | 4.5 PSH, no battery (tank buffered) |
| Array | 2,680 × 1.15 / (4.5 × 0.70) = ~975 Wp → 1 kWp class |
| Storage | Tank for 1-2 days: 12-24 m³ |
| Controller | VFD or MPPT pump controller matched to the pump, not a generic solar controller |
| Watch out | Irrigation has no autonomy requirement, which is why the battery disappears and the tank does the buffering. Friction in an undersized delivery pipe can add more head than the borehole depth. |
Reading these designs correctly
- Where the calculated array is far below the practical minimum, use the practical figure — small arrays have no room to absorb soiling, ageing or a run of cloudy days
- The battery is usually limited by discharge current, not by watt-hours, on sites with motors or radios
- Autonomy dominates cost. Going from 3 to 7 days roughly doubles the battery, which is often the largest single line item
- Every design here assumes no grid and no generator. Adding a small generator changes the economics completely but introduces fuel logistics
Use the calculator to run your own numbers, or send us the site details for a specification.