Batteries
What battery SoC settings should I use for load shedding in South Africa?
Set a dedicated reserve (often about 20–40% state of charge) for Stage slots, keep daily cycling above that floor for bill savings, and write both numbers on the handover sheet. Usable kWh on the quote is not the same as kWh left when Eskom trips at 20:00. Wrong SoC settings either flatten the pack every afternoon or leave you dark in Stage 4.
Updated 27 October 2026 · Illustrative ranges — not a formal quote, credit decision or legal advice.
Answer first: Ask the installer for two SoC figures — cycle floor for normal evenings and Stage reserve that the hybrid must not discharge below until the grid fails (or until you manually override). Then test one simulated outage before you trust the system.
Why one SoC number is not enough
Marketing DoD (depth of discharge) describes warranty maths. Load shedding needs a reserve so fridge, router, lights and a gas-ignition assist survive a 2.5–4 hour slot without hitting BMS disconnect. A pack warranted to 90% DoD that you empty to 10% SoC every sunny afternoon will not cover a late Stage 6 — DoD · usable kWh · Stage 4 sizing · Stage 6 sizing.
Practical starting bands (illustrative)
| Goal | Typical SoC idea | Watch-outs |
|---|---|---|
| Max bill self-use, mild Stage risk | Lower reserve (~15–25%) | Fine if shedding is rare and short; risky in winter Stage 4–6. |
| Balanced suburban hybrid | Reserve ~25–35% | Common homeowner brief — confirm against essentials kWh. |
| Backup-first / WFH / medical | Reserve ~35–50% | Less afternoon cycling; may need more sticker kWh. |
These are conversation starters, not engineering defaults. Essentials board watts × hours decide the reserve — essentials vs non-essentials · solar during shedding.
Grid-charge windows and TOU
On Cape Town-style TOU or Eskom Homeflex, decide whether the hybrid may grid-charge into the reserve before a published Stage slot. Blind grid-charge on a expensive peak block can erase bill savings; timed top-ups before evening shedding can protect WFH. Write the rule down — Cape Town TOU · Homeflex · grid-charge hub.
Geyser, stove and EV honesty
- Geysers and ovens on the backup board destroy reserves in minutes — geyser on backup · stove / oven.
- Most wallboxes should shed or sit off-backup during Stage — EV load management.
- Aircons on battery need explicit surge and kWh maths — aircon on battery.
Warranty and heat
Hot plant rooms and Highveld summer peaks stress packs. Keep ambient in the OEM band; Solar MD’s longer SA warranty examples (e.g. SS4160 12-year / 84 MWh class among Freedom Won, BlueNova, BYD, Pylontech peers) still assume correct install and SoC abuse limits — read the PDF, do not invent cycles — heat · warranty checks · cycles.
Handover sheet fields to demand
- Cycle floor SoC and Stage reserve SoC.
- Whether grid-charge into reserve is enabled, and on which tariff windows.
- Essentials board circuit list and measured watts.
- App screenshots after a 30-minute simulated outage test.
- Firmware version and who may change SoC later — firmware.
Document pack to keep with this answer
Store the handover SoC / load / tariff screenshots beside your CoC and SSEG reference. When a future installer or buyer asks why the system behaves as it does, that folder ends arguments faster than app folklore — read a quote · selling with solar.
Worked Stage evening sketch (illustrative)
Essentials draw 0.6 kW average (fridge, lights, router, laptops). A 2.5-hour Stage 4 slot needs about 1.5 kWh delivered. If your pack’s usable evening window above the Stage reserve is only 1.0 kWh, you will hit disconnect early — raise reserve, shed a load, or add parallel capacity. Do the same maths for Stage 6 nights stacked back-to-back.
Write the sketch on the quote cover next to sticker kWh. Buyers who only see “10 kWh battery” without SoC policy buy darkness — parallel expansion · add battery · fridge through shedding.
App schedules that fight each other
- Force-charge to 100% every afternoon “for safety” then enable heavy self-use can cycle the pack harder than the warranty desk expected.
- Calendar Stage prediction apps help only if the hybrid actually holds the reserve when the slot arrives.
- Guest mode / holiday mode that drains to empty before a trip leaves the house dark if shedding hits on return day — reset SoC before you leave — holiday home.
Installer red flags on SoC
- No written reserve — “the default is fine”.
- Reserve set to 5% to inflate marketed runtime.
- Grid-charge enabled on the most expensive TOU block with no explanation.
- No simulated outage test at handover.
Walk away or demand a revised brief — red flags · choose installer · check a quote.
Chemistry and peers
Most SA home packs are LiFePO₄. Cycle-life marketing still assumes moderate depth and temperature. Compare Freedom Won, Solar MD, BlueNova, BYD, Pylontech and peers on usable kWh, BMS limits and local claims desks — not on a single SoC screenshot — LiFePO4 vs NMC · batteries hub.
Morning sun recovery after a hard Stage night
After a deep Stage evening, the pack may wake at the reserve floor. Prioritise PV charge into the reserve before enabling heavy daytime self-use loads if another slot is scheduled. Homes that immediately run pool pumps and geysers at sunrise can enter the next shed under-charged. Align timers with the Eskom app forecast and your metro’s published slots when you can.
Hybrid grid-charge can top up before a known evening slot, but price it against TOU peaks — Cape Town and Homeflex customers should treat blind peak charging as a last resort — Cape Town TOU · Homeflex · pool pump.
Medical, WFH and security loads
List non-negotiable circuits: CPAP, networking, alarm, gate motor, fridge. Size reserve kWh to those first. Entertainment TVs and ironing boards do not belong on the same promise. If medical loads dominate, consider a longer autonomy target than the neighbour’s “lights and Wi-Fi” brief — and say so on the quote.
- Measure actual watts with a plug meter where safe.
- Photograph DB labels after essentials are final.
- Retest after any firmware or SoC change.
Related: UPS vs hybrid · runtime tool · load-shedding hub.
Seasonal retune
Winter production drops and Stage patterns change. Revisit reserve percentages at the equinoxes. A 25% reserve that worked in October may be thin in June if PV recovery is weak — winter production · cloudy days.
Share the SoC sheet with your insurer
Some household policies ask how long critical loads run. Your written Stage reserve and essentials watts answer that better than a brochure — keep both current after any change.
Reserve, grid-charge and export — three knobs
Min SoC / backup reserve protects Stage. Grid-charge windows refill before Stage on tariffs that allow it. Export limit caps what leaves the erf. Turning all three to “max comfort” without reading the bill is how fixed charges and peak TOU erase savings — grid charge · export limits · export vs self-use.
Worked evening reserve
If essentials need 2 kWh for a 2.5 h slot and you want 25% left at restore on a 10 kWh usable pack, do not arrive at 18:00 at 30% SoC. Pre-charge or shed earlier. Related: schedule strategy · Stage 4.
App vs reality
Photograph settings after every firmware update. Partners sometimes reset reserves during service visits — firmware · monitoring.
Altitude and heat as silent SoC thieves
Hot Highveld afternoons that derate charge current leave you below the reserve you thought you set — Highveld derate · battery heat · usable kWh.
Quick questions
Is 20% SoC reserve enough for Stage 6?
Only if essentials kWh fit. A large fridge + lights + Wi-Fi for four hours may need more usable kWh or a higher reserve — size the load, do not guess.
Should I drain to 0% every day for savings?
No. Hitting BMS disconnect regularly is hard on packs and leaves no Stage cushion. Use the warranty DoD as a ceiling, not a daily target.
Can I change SoC myself in the app?
Often yes, but record the change. After firmware updates, re-check that your reserve survived the flash.
Sources & related
- Solar News 24 — usable battery kWh
- Solar News 24 — Stage 4 battery sizing
- Solar News 24 — battery DoD