Inverter Sizing Calculator South Africa

🔋 Last Updated: May 2026 · SA Market Pricing · Load Shedding Optimised

🔋 Inverter & Battery Sizing Calculator — Enter Your Loads

Backup Hours Required

Size for the worst stage you experience

Battery Type

Lithium lasts longer but costs more upfront

Battery Bank Voltage

48V reduces current and cable losses

Appliances — tick ✓ to include in battery backup sizing

Appliance	Watts (W)	Qty	Backup ✓	Load (W)

✅ Sizing Complete — Recommended System

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Minimum Inverter Size

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Battery Bank Required

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Total Running Load

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Backup Load (essential)

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Energy Needed

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Battery Bank (Ah)

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× 100Ah Batteries

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Depth of Discharge

Approximate SA Market Cost Range (2026)

Inverter (supply only)

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Battery Bank (supply only)

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⚠️ For planning purposes only. All inverter and battery installations must be carried out by a registered electrician. A Certificate of Compliance (CoC) is required. Costs are indicative — obtain quotes from SESSA-registered installers.

Inverter and Battery Sizing for South African Load Shedding

Load shedding has made inverter and battery backup systems essential in South Africa. But an incorrectly sized system is either too small to handle your loads — leaving you in the dark during a 4-hour Stage 6 slot — or vastly oversized, wasting money on capacity you never use. Getting the sizing right requires two separate calculations: one for the inverter kVA and one for the battery bank capacity.

The Two Sizing Calculations — Formulas Explained

Inverter and battery sizing formulas

Total load (W) = Sum of all appliance watts × quantity Inverter kVA = Total load (W) × 1.25 (safety factor) ÷ 1000 Wh needed = Backup load (W) × Backup hours Battery Ah = Wh needed ÷ (Battery voltage × DoD) No. of batteries = Battery Ah ÷ 100Ah (round up) Lead-acid DoD = 0.50 (discharge to 50% for longevity) Lithium DoD = 0.80 (safe to discharge to 80%)

Why the 1.25 safety factor for inverter sizing?

Appliance nameplates show rated power, but motors — fridges, pumps, compressors — draw 3–5× their rated current at startup (inrush current). The 1.25 safety factor provides headroom for this surge. For motor-heavy loads, some installers use a 1.5× factor. Always round up to the next standard inverter size available in the SA market: 1kVA, 2kVA, 3kVA, 3.5kVA, 5kVA, 8kVA, 10kVA, 15kVA.

Lead-Acid vs Lithium LiFePO4 — Which is Right for South Africa?

Feature	Lead-Acid / AGM	Lithium LiFePO4
Upfront cost (100Ah)	R1,500–R2,500	R4,000–R8,000
Depth of discharge	50% (protect lifespan)	80% (safe limit)
Usable capacity (100Ah)	~50Ah effective	~80Ah effective
Cycle life	300–500 cycles	2,000–5,000 cycles
Charge time	8–12 hours	2–4 hours
Maintenance	Check water levels (flooded)	None
Weight (100Ah)	~28–30kg	~12–14kg
Best for	Tight budget, occasional use	Daily cycling, long-term value

For South African homes experiencing daily load shedding, lithium LiFePO4 batteries typically offer better 10-year value despite the higher upfront cost. At Stage 4 load shedding (2 slots per day, cycling twice daily), lead-acid batteries can reach end-of-life in 12–18 months if regularly discharged below 50%. Lithium under the same conditions can last 5–8 years.

Battery Voltage — Why 48V is Recommended for Home Systems

For any system above about 2kVA, a 48V battery bank is strongly preferred. Here is why: to deliver the same power, a 48V system draws one-quarter of the current compared to a 12V system. Lower current means thinner cables, less heat loss, smaller connectors, and reduced fire risk. A 3kVA inverter on 12V draws 250A from the battery — requiring very thick cables and heavy-duty connections. The same inverter on 48V draws only 62.5A — far more manageable.

SA load shedding rule of thumb: For a standard home wanting to keep lights, router, TV, fridge, and phone charging running through a Stage 4 slot (4 hours), a 3kVA inverter with 100Ah of lithium batteries at 48V is a practical and popular starting point. Many SA homeowners later add solar panels to the same hybrid inverter to reduce Eskom dependency further.

Popular Inverter Brands in South Africa (2026)

Victron Energy: Premium European brand, excellent local distributor support, modular and expandable. Industry standard for quality installations.
Deye: Popular hybrid inverter with built-in MPPT solar charger. Good value, strong SA market presence, compatible with most lithium batteries.
Sunsynk: Reliable hybrid inverter, large SA installer network, good app monitoring. Widely used in residential installations.
Solis: Competitive hybrid inverter, growing SA market share, good price-to-feature ratio.
Axpert / Voltronic: Entry-level budget options. Limited features compared to hybrids but reliable for basic backup without solar.

What Appliances Can You Run — Realistic Wattage Guide

LED lighting (per globe): 7–15W
WiFi router: 10–20W
Laptop: 45–90W
DSTV decoder: 30–50W
LED TV (50"): 80–120W
Fridge (modern, large): 100–200W average (cycles on/off)
Ceiling fan: 60–80W
Phone charger: 5–20W
Electric blanket: 100–200W
Microwave: 800–1,500W — high draw, use sparingly
Electric kettle: 1,500–2,400W — very high draw, use briefly
Air conditioner (9,000 BTU): 900–1,200W — very demanding on battery
Geyser (3kW): 3,000W — do not run on battery backup
Electric stove: 1,500–6,000W — avoid; use gas instead

Frequently Asked Questions

How do I calculate what size inverter I need in South Africa?

Add up the wattage of all appliances you want to run simultaneously during load shedding. Multiply by 1.25 for a safety factor. For example, if your essential loads total 2,000W: 2,000 × 1.25 = 2,500W minimum inverter output — requiring a 3kVA or 3.5kVA inverter. Always round up to the next standard size. This calculator does the calculation automatically based on your appliance list.

How many batteries do I need for my inverter in South Africa?

Calculate: Backup load (W) × Backup hours = Wh needed. Then: Battery Ah = Wh ÷ (Battery voltage × DoD). For lead-acid use 50% DoD; for lithium use 80% DoD. Example: 800W load for 4 hours at 48V lithium = 3,200Wh ÷ (48 × 0.8) = 83Ah — one 100Ah battery is sufficient. For lead-acid the same scenario requires 133Ah — two 100Ah batteries.

What is the difference between lead-acid and lithium batteries for inverters?

Lead-acid batteries cost less upfront (R1,500–R2,500 per 100Ah) but last only 300–500 cycles at 50% DoD — roughly 1–2 years of daily cycling. Lithium LiFePO4 costs more (R4,000–R8,000 per 100Ah) but lasts 2,000–5,000 cycles at 80% DoD — 5–10 years of daily use. For South African homes with daily load shedding, lithium typically delivers significantly better value over the system lifetime despite the higher upfront cost.

What size inverter do I need for load shedding in South Africa?

For lights, router, TV, phone charging and a fridge: a 2kVA–3kVA inverter is usually sufficient. To add a microwave or kettle (used briefly): 5kVA. To run a small air conditioner: 5kVA–8kVA, though this dramatically increases battery demand. Most South African homeowners choose 3kVA–5kVA as a practical balance for Stage 4–6 load shedding coverage.

Can I add solar panels to my inverter system later?

Yes — if you install a hybrid inverter (with MPPT solar charger) from the start. A hybrid inverter handles both battery backup and solar panel input, so you can add panels later without replacing the inverter. Pure battery inverters without MPPT cannot accept solar panels. Buying a hybrid inverter upfront is recommended even if solar panels are added later, as it avoids replacing the inverter twice.

Why is 48V recommended for home inverter systems in South Africa?

At 48V, a 3kVA inverter draws only about 62A from the battery — manageable with standard 35mm² cable. The same system at 12V draws 250A, requiring very heavy cable and connectors. Higher current means more heat, more cable losses, and greater fire risk. For any system above 2kVA, 48V is the practical and preferred choice. Most modern SA inverters (Deye, Sunsynk, Victron Multiplus-II) operate natively at 48V.

🔧 Related Artisan Tools

→DB Board Load Calculator — Check your board capacity before installing an inverter →Cable Size Calculator — Size the inverter feed cable correctly →Solar ROI Calculator — Calculate the return on a full solar + battery system

Inverter & Battery Backup Sizing Calculator — South Africa