Load Shedding Battery Backup Calculator

1. The Stage 6 Recharge Problem

Every load shedding calculator built for the US market assumes the same thing: a short, occasional outage followed by a long, guaranteed recharge window. That assumption breaks completely at Stage 5 and above. Eskom's Stage 6 schedule typically removes power for two four-hour blocks in a 24-hour cycle, which sounds survivable until you look at the gap between them. A home coming off a 4pm–8pm outage may only get four or five hours of grid power before the next block starts at 2am. If your battery didn't fully recharge in that window — from the grid, from solar, or both — you start the next outage already behind.

This is the recharge deficit problem, and it's the single biggest reason South African batteries fail years earlier than their datasheet suggests. A battery rated for 6,000 cycles at 80% depth of discharge is being tested against a very different reality: partial recharges, back-to-back deep discharges, and heat. Lead-acid and AGM batteries handle this badly. Their usable depth of discharge is genuinely closer to 50% if you want any meaningful lifespan, which means a "10kWh" AGM bank is really a 5kWh bank once you account for the buffer you need to protect it. Push past that repeatedly during Stage 6 and you're looking at battery replacement inside 18–24 months.

LiFePO4 (lithium iron phosphate) batteries change the math. A C1-rated LiFePO4 pack can be discharged to 80–90% depth of discharge daily without materially shortening its life, and it accepts a faster charge rate — meaning it can actually refill during a short four- or five-hour grid window where an AGM bank would still be topping up. Pairing that battery with rooftop solar removes the dependency on the grid window entirely: the sun doesn't care what stage Eskom has declared. For anyone planning around Stage 5 or 6 with any seriousness, LiFePO4 plus solar charging isn't the premium option — it's the only configuration that survives the schedule. If you're still comparing chemistries, our comprehensive solar battery selection guide breaks down cycle life, DoD and cost-per-cycle for every major chemistry sold in South Africa.

2. Stage-by-Stage Sizing Breakdown

Sizing correctly means working from two numbers: your continuous load in watts, and the number of hours you need to cover without grid power. Multiply load (kW) by hours to get kWh needed, then add a depth-of-discharge buffer so the battery isn't run flat every night.

Worked example: a medium home (650W base load) running lights, router, TV, fridge and phone charging draws roughly 430W continuous. At Stage 4 (8 hours off), that's 3.44kWh of raw draw. Add a 25% depth-of-discharge buffer and you're at 4.3kWh needed — but the 10kWh minimum in the table above still applies, because it accounts for fridge compressor surge cycles, an imperfect inverter efficiency (typically 90–94%), and the fact that Stage 4 can escalate to Stage 6 with a few hours' notice. Sizing to the bare arithmetic leaves zero margin; sizing to the stage-band minimum leaves room to actually live through an escalation.

Two variables move that worked example more than people expect: appliance duty cycle and ambient temperature. A fridge doesn't draw its rated 150W continuously — it cycles the compressor on and off, averaging closer to 35–40% of its rated draw over an hour, but the calculator above treats it as continuous because that's the safe assumption once an outage stretches past a couple of hours and the compressor has to work harder to hold temperature after the door's been opened a few times. Battery capacity also derates in heat: a LiFePO4 pack mounted in a garage or a north-facing storeroom in Gauteng summer can lose several percent of usable capacity compared to its rated figure at 25°C, which is one more reason the stage-band minimums in the table build in headroom rather than tracking the bare arithmetic.

The other number worth sitting with is inverter efficiency loss, because it compounds with everything above rather than sitting apart from it. A hybrid inverter converting DC battery power to AC household power typically loses 6–10% of the energy in that conversion. On a 10kWh battery that's roughly 700Wh to 1kWh you never actually get to use, before appliance duty cycles or temperature derating are even considered. None of these losses are dramatic in isolation, but stacked together they're exactly why the stage-band minimums in the sizing table sit meaningfully above what a first-pass wattage-times-hours calculation suggests, and why installers who quote strictly to the bare arithmetic are setting a household up to run flat before the outage actually ends.

If you're in a smaller footprint and want a tighter number specific to a flat or townhouse rather than a full house, our small house solar sizing tool runs the same math against a smaller base load profile.

3. kVA vs kW De-mystified

This is where more South African buyers lose money than any other single spec. An inverter's kW rating is its real, usable power. Its kVA rating includes "apparent power" — a figure inflated by the power factor of whatever you're running. Most home inverters are quoted at a 0.8 power factor, which means an 8kVA inverter genuinely only delivers about 6.4kW of continuous real power. Installers who quote kVA without explaining this aren't necessarily being dishonest, but the buyer who assumes kVA equals kW ends up with an inverter that trips under a load it should have handled comfortably.

The failure mode is predictable: a geyser element, a pool pump and a kettle switch on within the same few seconds, the real power draw exceeds the inverter's true kW ceiling even though the kVA number "should" have covered it, and the inverter trips and drops the whole house — including the fridge and router you were trying to protect. The fix is arithmetic, not a bigger budget: take your continuous load in kW, divide by 0.8, and that's the minimum kVA rating you need. Going the other direction — buying by kVA number alone — is how buyers end up spending thousands more on the "next size up" after their first inverter can't cope.

4. Battery-Only Backup vs. Solar Hybrid

Battery-only backup is cheaper upfront and simpler to install: a battery, an inverter or UPS, and a changeover switch. It solves Stage 1–4 reasonably well, provided the grid window between outages is long enough to fully recharge. Its ceiling is exactly the recharge deficit problem covered above — it has no independent way to top up when the grid itself is the constraint, so it degrades fastest exactly when you need it most, at Stage 5 and 6.

A solar hybrid system — panels, a hybrid inverter, and the same battery bank — costs more initially but breaks the grid dependency entirely. The battery recharges from sunlight regardless of what stage is declared, which means outage duration stops being the limiting factor. The trade-off is roof space, a longer install timeline, and a higher initial outlay. For a household already close to the top of the "battery-only" budget tier, the honest advice is usually to add panels rather than oversize the battery: a bigger battery with no independent charge source just fails slower, it doesn't stop failing.

Rural properties and smallholdings carry an extra wrinkle worth flagging here: borehole and well pumps draw a hard surge on start-up that a small inverter can't absorb even if its continuous rating looks fine on paper. If that's part of your load, size it separately using our solar well pump calculator rather than folding it into the household essentials figure above.

There's also a middle path worth naming, because most suppliers present this as a binary choice when it doesn't have to be one. A household can install battery-only backup now, sized correctly for Stage 1–4, and add panels later once budget allows — provided the inverter purchased upfront is a hybrid unit rather than a basic UPS-style inverter. A hybrid inverter has the charge controller and DC input already built in for solar, so panels can be added at any point without replacing the core of the system. Buying a non-hybrid inverter to save a few thousand Rand today is the most common regret we hear about a year later, once Eskom has escalated a stage and the household wants to add solar to an inverter that was never built to accept it.

5. Updated 2026 Rand (ZAR) Pricing Table

The COC is not optional and not a formality — insurers increasingly ask for it before paying out on any claim involving fire or electrical damage where a battery system is present on the property. Budget for it from the outset rather than treating it as an add-on once the install is already signed off. For a full breakdown of panel pricing by wattage and brand tier, see our 2026 solar panel cost guide, and to track what the system should be saving you monthly against Eskom's rising tariff, run the numbers through our monthly solar savings calculator.

Two pricing traps show up repeatedly in South African quotes. The first is a battery quoted without its Battery Management System (BMS) itemised separately — some suppliers bundle a weaker BMS to hit a lower headline price, and a weak BMS is what fails first under the deep, repeated cycling that Stage 5–6 demands, not the cells themselves. Ask for the BMS brand and its rated continuous discharge current specifically. The second trap is a labour quote that excludes DB board modification — if the geyser and stove strategy in section seven below applies to your install, splitting the distribution board is additional electrician time that some quotes leave out to look more competitive on paper, then add back in as a "variation" once work has started.

6. Section 12B Tax Rebate Guide (2026)

Section 12B of the Income Tax Act allows a 100% deduction in the first year for qualifying renewable energy assets — solar panels, batteries and associated inverters — when the asset is used to generate income. This means a registered business, a sole proprietor with a home office, or a landlord installing the system in a rental unit can deduct the full cost against taxable income in the year the system is brought into use, rather than depreciating it over several years.

The qualification hinge is trade use, not ownership type. A homeowner installing a system purely for a private residence with no business or rental activity attached does not qualify under 12B — this is a business incentive, not a household solar rebate. Where a portion of the home is used for income-generating work, practitioners typically apportion the deduction to the business-use percentage of the property. Because this determination affects real tax liability, treat the numbers in the calculator above as an estimate to bring to a registered tax practitioner, not a final figure to file with SARS.

Documentation matters as much as eligibility here. SARS wants proof the asset was brought into use during the tax year being claimed — keep the COC, the supplier invoice showing the commissioning date, and, where the deduction is apportioned, a record of the business-use percentage of the property (square meterage of a home office against total floor area is the common method). Claiming the deduction without this paper trail is the most common reason a otherwise-valid 12B claim gets queried on review, not the underlying eligibility itself.

7. Geyser & Heavy Appliance Management Strategy

The geyser is the single element that breaks more load shedding budgets than any other appliance in the South African home, purely because of its 3kW draw. Trying to keep a geyser on battery power through a Stage 6 outage means sizing an entire system around one element rather than the household. Three strategies solve this without that cost:

Timers. The cheapest fix. Set the geyser to heat only during Eskom's guaranteed on-window and switch it off before the next outage block — water stored in an insulated tank stays hot for hours with the element off, so you lose nothing in comfort while removing the 3kW draw from your battery calculation entirely.

Solar geysers and heat pumps. A solar geyser (or a heat pump running on a fraction of the element's wattage) removes the geyser from the electrical load conversation altogether, heating water directly from the sun or from ambient air instead of drawing from the battery-backed circuit.

DB board split-circuit setups. The structural fix: an electrician splits the distribution board so essential circuits (lights, router, fridge, plugs) sit on the battery-backed side, while the geyser, stove and other heavy elements stay on an unprotected circuit that simply goes off during load shedding, same as it always did before you had a backup system at all. This is the setup we recommend by default — it keeps the battery sized to what you actually asked for in Step 3 above, not inflated by appliances you were never planning to run off it. If your protection concern extends beyond the geyser to flood or water-ingress risk during outages, our solar sump pump power calculator covers sizing for that circuit separately.