What Size Inverter (kVA) Do I Need?

The most common question we hear: 'I want a solar inverter — what size should I buy?' The answer lives in your appliance list, not in a generic recommendation. Here is the exact method our engineers use.

The Four-Step Load Calculation

• Step 1 — List appliances: write down every device you want the inverter to power simultaneously at peak usage.
• Step 2 — Note running watts: use the nameplate wattage or measure with a meter. Resistive loads (bulbs, kettles) = nameplate. Motor loads (fridge, pump, AC) = nameplate × 0.8 for running.
• Step 3 — Find the biggest surge: multiply the largest motor's running watts by 3 to estimate startup. A 200 W fridge motor surges to ~600 W; a 1.5 HP pump (1 120 W running) surges to ~3 360 W.
• Step 4 — Add 20 % buffer: sum all running watts, add 20 % for losses and heat derating, then ensure the inverter's surge rating exceeds your worst-case startup.

Quick Reference by Home Size

• Single room / studio: 2 fans, 1 TV, 4 LED bulbs, phone charging → ~300 W running → 1 kVA inverter minimum (1.5 kVA recommended).
• 2-bedroom flat: add 200 W fridge, 6 bulbs, laptop → ~700 W running, ~800 W surge → 1.5–2 kVA inverter.
• 3-bedroom bungalow: 1 fridge, 4 ceiling fans, 2 TVs, 6 bulbs, 0.75 HP pump → ~1 400 W running, ~2 500 W surge → 3 kVA inverter.
• 3-bedroom duplex with small AC (1 HP window unit): ~2 600 W running, ~4 800 W surge → 5 kVA inverter.
• 4-bedroom duplex / SME: 1.5 HP AC + pump + full lighting + multiple fridges → 5–6 kVA inverter.

Why Heat Derating Matters in Nigeria

Inverter manufacturers rate output at 25 °C. Harmattan or dry-season afternoons in Kano, Abuja, or Enugu regularly hit 38–42 °C in a poorly ventilated room. At 40 °C, most inverters derate to 85–90 % of rated output, and thermal protection may reduce this further. If your load calculation gives 3 kW, buy a 3.5–5 kVA unit — the headroom pays for itself in longevity and prevents nuisance shutdowns.

24 V vs 48 V — Which Battery Voltage?

• 1–2 kVA systems: 24 V is fine. Two 12 V 200 Ah batteries in series give 400 Ah at 24 V — plenty for a small flat.
• 3–6 kVA systems: 48 V is strongly recommended. Same 400 Ah capacity, but half the current → thinner cables → less heat → better efficiency.
• Never try to run a 5 kVA load on a 24 V system — cable sizing and battery discharge current become dangerously high.

Matching Inverter Size to Our Product Range

• 1.5–3 kW / 24 V: Gennex 3 kW 24 V MKS Plus (1 500 W MPPT built in) or Itel Hybrid 3 kW 24 V.
• 5 kW / 48 V: Growatt SPF 5000 Smart Hybrid (4 000 W MPPT), Dyness Hybrid 5 kW, or Gennex 5 kW 48 V MKS Zero (4 000 W MPPT).
• 6 kW / 48 V: Growatt SPF 6 kW 48 V with 8 000 W MPPT (best for rapid charging of large battery banks) or Itel Hybrid 6 kW 48 V.