Off-Grid Satellite Power: Calculating 12V and Solar Requirements

Start with the measured load

The terminal is only one part of the power system. Include the router, Ethernet equipment, voltage converters and inverter standby consumption. Measure the assembled system over a representative period if possible. Average consumption, startup demand and maximum input rating describe different things. A supply that handles the average but collapses during a short peak can cause unexplained reboots.

Calculate daily energy

Energy in watt-hours equals power in watts multiplied by hours. For an illustrative 40 W load running eight hours, the devices consume 320 Wh. At an assumed end-to-end conversion efficiency of 85%, the battery must deliver about 376 Wh. At a nominal 12.8 V, that is approximately 29.4 Ah. These assumptions are deliberately explicit so you can replace them with measurements from your own kit.

Allow for usable capacity

A 12.8 V, 100 Ah battery has a nominal energy of 1,280 Wh. If you deliberately budget 80% as usable and assume 85% conversion efficiency, about 870 Wh reaches the load, or roughly 21.8 hours at 40 W. This is a planning example, not a battery specification. Chemistry, temperature, ageing, reserve requirements and the battery management system affect what is actually available.

Estimate solar production

Use peak-sun-hours for the location and season, not hours of daylight. An illustrative 200 W array with four peak-sun-hours and a 75% overall harvest factor produces 600 Wh in a day. That could cover the example load with some margin, but a cloudy winter day may deliver much less. Include the fridge, lights and charging loads before deciding the array is sufficient for the whole camp.

Plan consecutive poor days

Set a reserve target and decide which loads can be reduced. Turning broadband off when not needed may save more energy than changing a small accessory. Keep enough stored energy for essential communications and do not assume tomorrow's solar production will refill a depleted battery. Monitor voltage and state of charge with equipment appropriate to the battery chemistry.

Choose the right power path

For Mini, follow the manufacturer's supported input and cable requirements rather than adapting a random lead. Long low-voltage runs can lose voltage under load. A correctly designed DC setup may avoid some inverter losses, but polarity, fusing, cable size and connector sealing still matter. Permanent vehicle or building electrical work should be designed and installed by a suitably qualified person.

Commission before leaving

Run the full system from its real battery for several hours, including calls and downloads. Check temperatures and whether reboot events coincide with other appliances starting. Record consumption overnight if continuous operation is planned. The best battery calculation is still only an estimate until the complete system has passed this practical test.