Solar Power Calculator for IoT Field Sites

Off-grid solar power is essential for remote IoT installations. This guide provides a practical calculator with worked examples.

Step 1: Calculate Daily Energy Consumption

Sum the wattage of all devices × hours of operation per day. Example: RTU (1W × 24h) + 4G router (2W × 24h) + radar sensor (0.5W × 24h) = 84 Wh/day.

Step 2: Add Safety Margin

Multiply by 1.5 to account for inefficiencies, aging, and unexpected loads: 84 × 1.5 = 126 Wh/day.

Step 3: Size Solar Panel

Solar panel size (W) = Daily energy (Wh) / Peak Sun Hours / 0.8 (system efficiency). In Bangkok (4.5 peak sun hours), need 126 / 4.5 / 0.8 = 35W. Round up to 50W panel for headroom.

Step 4: Size Battery

Battery capacity (Wh) = Daily energy × days of autonomy / 0.7 (depth of discharge). For 5 days autonomy: 126 × 5 / 0.7 = 900 Wh = ~75 Ah at 12V.

Step 5: Verify Temperature Effects

Batteries lose capacity in cold weather. At 0°C, lead-acid batteries deliver only 70% of rated capacity. Lithium batteries perform better in cold but cost more.

Worked Example: Hydrology Station

Devices: 1 RTU + 1 4G router + 1 radar sensor + 1 rain gauge. Daily consumption: 84 Wh. Solar: 50W panel. Battery: 100Ah lithium (12V). Works year-round in tropical climate.