How many days of autonomy does a remote solar power system need?
Autonomy is the number of days the system can carry the load with no solar generation at all. AS/NZS 4509.2, the Australian standard for stand-alone power system design, gives the guidance most Australian designers work to: 2 days where an automatic generator is fitted, 2–3 days with manual generator control, and 4–5 days for a solar, wind or hybrid system with no generation backup at all.
ModX2 is configured with one, two or three LiFePOâ‚„ battery modules. As an indication, at a 100–200 W continuous load that gives roughly 1.5–2 days, 2.5–4 days and 4–6 days of autonomy respectively. Two modules is the standard configuration. Use the ModX2 calculator to enter your actual site loads and see the recommended battery configuration against your daily consumption.
Three things move those numbers. Any supplier who quotes autonomy without them is guessing:
- The maximum contiguous run of low-solar days at your latitude and season
- The capacity the battery will still have at end of design life, not when new
- The actual measured load, not the estimated one For rail applications, note that AS 7703 clause 4.2.3 requires solar battery sizing to explicitly account for both the cloudy-day run and end-of-life capacity degradation, an estimate that ignores either will not survive design review.