Batteries
What is battery depth of discharge (DoD) for solar in South Africa?
Depth of discharge (DoD) is how much of a battery’s rated capacity you are allowed to use in normal operation. Usable energy is roughly nameplate kWh × allowed DoD. A “10 kWh” pack at 90% DoD gives about 9 kWh usable — which is the number that should drive Stage 6 runtime maths, not the sticker.
Updated 26 October 2026 · Illustrative ranges — not a formal quote or legal advice.
Answer first: Sales stickers shout “10 kWh.” Your fridge cares about usable kWh. If the manufacturer specifies 90% DoD, plan on ~9 kWh. If another pack allows only 80% in the warranty fine print, a “larger” sticker can deliver less. Always convert before comparing quotes or Stage 6 runtimes.
DoD, SoC and cycle life
DoD is how deep you go; state of charge (SoC) is how full you are. Deeper daily cycling can wear some chemistries faster. Modern home LiFePO₄ packs are commonly warrantied for high DoD (often ~90–100% of usable) with cycle/throughput caps — read the PDF — cycles & warranty, LFP vs NMC.
Worked example
| Sticker kWh | Allowed DoD | Usable kWh | ~Hours at 1 kW essentials |
|---|---|---|---|
| 5 | 90% | 4.5 | ~4.5 |
| 10 | 90% | 9 | ~9 |
| 15 | 90% | 13.5 | ~13.5 |
| 10 | 80% | 8 | ~8 |
Inverter efficiency, low-temperature derating and surge loads shorten real runtime — runtime tool, Stage 6.
Why installers leave headroom
Holding a 10–20% SoC floor can preserve surge capacity and reduce stress. That operational reserve is another reason sticker kWh ≠ overnight comfort.
Warranty traps tied to DoD
Some warranties require staying inside documented DoD / current limits. Parallel mismatched packs, overheating garages, or firmware set to 100% every day against guidance can complicate claims. Soft Solar MD and peer LFP brands publish throughput figures — compare PDFs, not slogans. BlueNova SBB street prices (e.g. EcoHub BN52V-280-14.5k listings) still need usable-kWh conversion on the quote.
Lead-acid contrast
Legacy lead-acid hated deep daily DoD. If a quote still pushes lead for daily solar cycling, ask why. LFP dominates serious residential SA quotes for a reason.
EV packs vs house packs
Do not assume traction-battery DoD rules apply to stationary LFP. Different BMS, warranties and thermal designs. V2H dreams do not change house-battery maths today — V2H.
Quote checklist
- Usable kWh at the warrantied DoD stated in writing.
- Recommended daily DoD vs emergency DoD.
- Throughput / cycle clause summarised in plain language.
- Temperature limits for your install location.
SA caveats
Hot roof cavities and unventilated battery cupboards derate performance. Educational only.
Quick FAQ
Is 100% DoD safe? Only if the OEM’s usable capacity definition and warranty say so.
Does higher DoD mean better? Only with chemistry and warranty to match.
Can software change DoD? Installers set floors/ceilings — ask what they programmed.
How to read a quote without getting lost
Demand a single-line diagram, a clear labour vs hardware split, and the assumptions behind any “payback” number. If savings use last year’s crisis tariff increases forever, re-run the model flat. Ask what happens if export credits fall or fixed network charges rise at the next July schedule. Keep emails — verbal promises about municipal approvals evaporate when staff rotate.
Money first, then resilience
South African buyers often flip the order: they buy for Stage 6 anxiety and only later discover the bill maths. Flip it back. Size for self-consumption and tariff reality, then layer enough battery for the outages you actually live through. A slightly smaller compliant system that is registered and monitored beats a oversized grey-import stack that never finishes SSEG.
Documents to keep in one folder
CoC, inverter NRS certificate, battery warranty PDF, SSEG approval, as-built diagrams, serial numbers, and app login details. When you sell the house or claim warranty, this folder is worth more than another brochure. Photograph the DB before and after works. Store cloud copies — paper in a garage floods.
Common salesperson scripts to challenge
“Export will pay for the system,” “batteries are optional fluff,” “you don’t need municipal registration,” “this inverter is the same as the NRS one,” “V2G will make you money next year.” Each script has a grain of truth wrapped around a costly exaggeration. Ask for the primary metro PDF or certificate page, not a WhatsApp forward.
Maintenance that actually protects savings
Glance at the monitoring app weekly for unexpected grid import spikes. After hail or severe dust, inspect panels from the ground. Keep vegetation from shading the bottom row. Test the changeover / backup path before the next heavy shedding week — not during it. Replace surge devices after known nearby strikes if your electrician recommends it.
When to get a second opinion
Any quote that requires a supply upgrade, three-phase conversion, roof structural steel, or estate litigation risk deserves a second installer or an independent assessor. Comparison is why Solar News 24 pushes structured quote briefs — different firms catch different constraints on the same roof.
Putting this advice to work in a South African suburb
Start with last winter’s municipal bills and a simple spreadsheet: kWh imported, fixed charges, and any estimated kilometres if an EV is in the picture. Walk the DB with a registered electrician before you fall in love with a hardware brand. Confirm whether your roof needs structural sign-off and whether the estate has rules about visible conduit. If solar is part of the plan, decide export vs zero-export early because meter changes and prepaid migrations (especially City Power exporters moving to TOU conventional) alter the savings story. For batteries, insist on LiFePO₄ chemistry for home cycling unless you have a specialist reason otherwise, and read usable kWh and warranty throughput — not only the sticker kWh. For EV charging, default to a ~7.4 kW Type 2 wallbox with load management on a dedicated circuit and a CoC. Use public DC for travel corridors, comparing live app rates (DriveElectric’s documentation of SAEV Richmond near R3.49/kWh versus GridCars near R7.35/kWh is a reminder that prices diverge). Keep Stage 6 cover sized to essentials first; do not empty the house battery into the car unless the system was designed that way. Re-check July tariff annexures every year. None of this is glamorous — it is how SA households keep more rand while staying on the right side of SANS 10142, NRS 097 and municipal SSEG desks.
If you only remember four numbers from the wider Solar News 24 desk: metro export credits roughly 108–185 c/kWh incl. VAT in 2026/27; home EV energy often R53–R85 per 100 km at typical residential rates; wallbox all-in often R17k–R35k+; and NERSA’s ≤100 kW distributor registration vs above-100 kW NERSA path. Everything else is detail that belongs on your quote checklist and in your document folder.