Inverter & Battery Backup Sizing Calculator for South Africa
Size your inverter and battery bank for load shedding. Add your appliances, set backup hours, choose lead-acid or lithium, and get instant kVA and Ah results for the SA market.
Quick answer: Add up the wattage of all appliances you want to run during load shedding, then multiply by 1.25 for a safety factor to get the required VA. For example, 2,000W of essential loads needs approximately 2,500VA, sized up to the nearest standard inverter rating.
Inverter & Battery Sizing Calculator
Enter Your Loads
| Appliance | Watts (W) | Qty | Backup ✓ | Load (W) |
|---|
⚠️ 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.
How to Use This Calculator
- Select backup hours required4 hours covers most Stage 4 to 6 slots. Size for the worst stage you experience.
- Select battery typeLithium LiFePO4 for better long-term value, or lead-acid/AGM/gel for a lower upfront cost.
- Select battery bank voltage48V is recommended for most home systems above 2kVA, since it reduces current and cable losses.
- Add appliances and tick BackupEnter each appliance's watts and quantity, then tick the Backup column for anything you want running on battery during load shedding. Leave high-draw items like geysers and stoves unticked.
- Click CalculateResults size your inverter from total load with a 1.25 safety factor, and your battery bank from the backup-only load and hours at the correct depth of discharge, plus an approximate 2026 SA market price range.
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
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, such as fridges, pumps and 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, which is far more manageable.
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
Add up the wattage of all appliances you want to run simultaneously during load shedding, then multiply by 1.25 for a safety factor to get the required VA. For example, if your essential loads total 2,000W: 2,000 × 1.25 = 2,500VA (2.5kVA), requiring a 3kVA inverter. Always round up to the next standard inverter size.
Calculate the energy needed: Essential load (W) × Backup hours = Wh required. Then: Battery Ah = Wh ÷ (Battery voltage × Depth of discharge). For lead-acid batteries, use 50% DoD to protect battery life. For lithium (LiFePO4), 80% DoD is safe. Example: 800W load for 4 hours at 48V with 50% DoD = 3,200Wh ÷ (48 × 0.5) = 133Ah: two 100Ah batteries in parallel.
Lead-acid batteries (including AGM and gel) cost less upfront (approximately R1,500–R2,500 per 100Ah) but must only be discharged to 50% to achieve their rated cycle life of 300–500 cycles. Lithium LiFePO4 batteries cost more (R4,000–R8,000 per 100Ah) but can be discharged to 80%, last 2,000–5,000 cycles, charge faster and have no maintenance requirements. For most South African load shedding applications where the battery cycles daily, lithium offers significantly better value over a 5–10 year horizon.
For essential loads only (lights, router, TV, phone charging, a few plugs): a 1kVA–2kVA inverter is sufficient. To also run a fridge and one or two appliances: 3kVA–5kVA. To run a geyser, stove or air conditioner: 5kVA–10kVA, though these high-power appliances dramatically reduce battery runtime and require large battery banks. Most South African homeowners choose 3kVA–5kVA as a practical compromise for stage 2–6 load shedding.
Popular and widely supported inverter brands in South Africa include Victron Energy (premium, European, excellent local support), Deye (popular hybrid inverter with solar MPPT, good value), Sunsynk (reliable hybrid, strong SA distributor network), Voltronic (budget-friendly, widely used) and Axpert (entry-level, limited features). For a solar-ready hybrid inverter that handles both load shedding and solar panels, Deye and Sunsynk are among the most popular choices in the SA market in 2026.
Yes, if you buy a hybrid inverter (also called a solar inverter or MPPT inverter) from the start, you can add solar panels later. A pure battery/inverter system with a non-solar inverter cannot be upgraded to solar without replacing the inverter. If budget allows, buying a hybrid inverter with MPPT charge controller upfront is recommended, even if you add panels later, as it avoids double the installation costs. Check the inverter's maximum solar input (PV input voltage and MPPT capacity) before purchasing panels.
Running a 3kW geyser on battery power is generally not recommended: it drains a 100Ah battery in under 30 minutes at full load. Heat pump geysers use 900W–1.2kW and are more practical on a 3–5kVA inverter. Solar-only geysers avoid the problem entirely.
A 100Ah lithium (LiFePO4) battery stores approximately 1.2kWh of usable energy. Running a 300W load (lights, TV, Wi-Fi, fan), it lasts approximately 3–4 hours. A 150Ah lithium battery gives 4.5–6 hours at the same load. Lead-acid batteries provide 50–60% of rated capacity: a 100Ah lead-acid effectively gives 50Ah usable.
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.