Solar & Backup Sizing Calculator (SA)

Estimate inverter size (kW), battery capacity (kWh) and PV array (kW). Uses South African peak-sun-hours.

Inputs

Tip: start with essentials only
Essentials during outages (Wi-Fi, lights, TV, fridge cycling, a few plugs).
Maximum simultaneous watts your essentials will draw.
Peak-sun-hours (PSH) ≈ usable sun per day. Use winter PSH for conservative design.
Extra PV to recharge batteries within chosen period.
Assumptions: Lithium DoD 90% η 95%, Lead DoD 50% η 85%, PV losses per selection, inverter efficiency 92%. Results are indicative—use a qualified installer for final design and CoC.

Recommended sizes

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Inverter (continuous) kW (surge factored)
—
Usable battery needed kWh
—
Nameplate battery size kWh (chemistry adjusted)
—
PV array size kW

Runtime check

Average load used— kW
Estimated runtime on battery— hours
Runtime ignores PV during outage and assumes 92% inverter efficiency.

Next steps

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How we calculate

  • Inverter: peak load × surge factor (rounded up).
  • Battery (usable): (daily kWh ÷ 24) × autonomy hours.
  • Battery (nameplate): usable ÷ DoD ÷ round-trip efficiency.
  • PV array: daily kWh × (1 + daysPV) ÷ (PSH × system-loss factor).
  • Runtime check: usable × 0.92 ÷ average load.

These are indicative; site conditions, wiring, voltages, compliance (SANS/CoC) and winter sizing can change outcomes.