Performance
How much solar power do you get on cloudy or rainy days in South Africa?
On heavily overcast Cape or Highveld days, a rooftop array may produce only 10–40% of its clear-sky yield — sometimes a brief bump from bright cloud edge, sometimes near-zero in winter drizzle. That is why hybrids pair PV with batteries and, when needed, scheduled grid-charge before shedding. Design for annual self-use, not every afternoon looking like December.
Updated 27 October 2026
South Africa’s solar resource is excellent on an annual basis — and still moody week to week. Portals that show 28 kWh on Saturday and 4 kWh on Sunday are normal, not broken.
Order-of-magnitude expectations
| Sky | Share of clear-day yield (rule of thumb) | Owner move |
|---|---|---|
| Clear Highveld / clear Cape summer | 100% baseline | Shift loads into sun |
| Light haze / thin cloud | ~60–90% | Watch MPPT; still useful |
| Heavy overcast | ~10–40% | Lean on battery; delay laundry |
| Persistent winter rain | ~5–20% for hours | Grid import / grid-charge plan |
Coastal drizzle and Highveld thunderstorm afternoons behave differently — thunderstorms can include bright breaks with short production spikes. Site-specific monitoring beats memes.
Why the battery still earns its keep
Grey mornings before a shedding slot are when grid-charge before shedding is rational. On sunny weeks, keep that setting off so PV can refill. Essentials-board discipline matters more in weather weeks than in January — essentials vs non-essentials · battery for Stage 6.
Design implications
- Size arrays for annual kWh and self-use, then stress-test a 3-day low-yield stretch.
- East/west splits can smooth morning/evening shoulder cloud better than a pure west array on some roofs.
- Do not promise “off-grid through June” with a 5 kWh pack and a kettle addiction.
- Modest DC oversize on a hybrid is common; doubling the array only for three grey weeks rarely pays — sizing guide.
Heat pumps, geysers and grey days
Element geysers will happily flatten a battery on a rainy evening if left on the backup board. Prefer timers, heat pumps on sun hours, or keep water heating off backup — water heating hub · whole-home order.
Maintenance in the wet season
- Check for ponding on poorly pitched modules after first storms.
- Confirm trunking and roof flashing — penetrations.
- After dusty dry months, a clean can restore noticeable yield — cleaning.
- Watch inverter derating on hot humid days even when the sky looks bright.
Reading the portal without panic
Compare like-for-like: same weekday, similar weather. A single 4 kWh day after a week of 25 kWh days is weather. A week of 4 kWh days in January with clear satellite imagery may mean a string fault, tripped isolator, or severe soiling. Call the installer with screenshots, not vibes — fault codes.
Payback still works annually
Monthly savings swing with yield. Judge payback on 12 months and on tariff reality — monthly savings · payback by metro. Winter is when self-use discipline and heat-pump timing matter most.
Bill modelling on a grey week
Take last winter’s worst seven consecutive days of production (or your installer’s irradiance estimate cut by 40–60%). Re-run self-use: geyser timer still on sun hours, laundry deferred, EV charge delayed to the next clear afternoon. If the model only works on a perfect Highveld October day, the savings claim on the quote cover is marketing.
Export credits on grey days are tiny — Cape Town combined residential feed-in ≈152.93 c incl., City Power ≈143.29 c, eThekwini ≈184.60 c — so design around avoided import, not cloudy-day exports. Related: winter production · self-use · metro tariffs.
Battery behaviour when PV is thin
Set grid-charge / load-shedding calendars so the pack is not empty at 16:00 ahead of a Stage slot on a rainy Tuesday. Thin PV + empty battery + dinner load is how “solar does nothing in rain” stories start — usually a settings issue, not a panel failure. Monitoring checklist: numbers to watch · grid charge in shedding.
Keep the winter file next to the sunny marketing slide when you compare quotes — read a quote.
Quick questions
Does rain clean panels enough?
It helps, but sticky pollution and bird mess still need occasional manual cleaning.
Is my inverter faulty if production is low in rain?
Usually not. Compare to neighbours or a satellite irradiance estimate before calling out warranty.
Do bifacial panels help in cloud?
Slightly on bright ground reflections; they do not invent sun — mono vs bifacial.
Where this sits on the Solar News 24 desk
Read next: home solar pillar, costs & savings, metro tariffs 2026/27, and how to size a system. For EV households, pair with the EV charging guide (DriveElectric / SAEV cost cites). Always verify figures on your own bill and distributor schedule — municipal tariffs change every July.
Worked week — Cape winter example
A 6 kWp north array that averages 24 kWh on clear summer days might deliver 8–12 kWh on mixed winter days and 3–6 kWh on persistent drizzle. A 10 kWh usable battery that entered Monday at 40% SoC after Sunday shedding will not refill on solar alone by Tuesday evening. Schedule grid-charge before the next slot, keep the geyser off backup, and judge the plant on the month — not the gloomiest Tuesday.
Irradiance vs inverter faults
Before logging a warranty call, note ambient temperature, check DC isolators, and compare string voltages in the app. Many “broken solar” tickets are weather plus a tripped breaker. Keep a simple log: date, kWh, sky note, SoC morning/evening.
Tariff angle — cloudy weeks still cut the high block
Even a grey Cape week that delivers 30–40% of clear-sky yield can still shave the expensive upper Home User block. If your bill sits above 600 kWh at ~469 c/kWh, every daytime kWh the array still produces is worth nearly R4.70 avoided — far more than the ~153 c export credit. Size expectations down for June–August, not the business case. Pair with load shifting: run the dishwasher and heat-pump boost in the brightest mid-day window the portal shows.
Battery reserve policy for bad weather
Many hybrids let you raise the minimum SoC before a forecast multi-day front. Holding 30–40% overnight burns a little self-use arbitrage but keeps lights and fridge through a second Stage evening when PV recharge is thin. Grid-charge-before-shed remains the other lever when the metro is on — grid-charge guide. Do not empty the pack every sunny afternoon “because solar is free” if tonight’s Stage 4 slot is already published.
Coastal mist vs Highveld thunderstorms
Cape north-westers and False Bay mist flatten irradiance for hours; Highveld storms slash output in short violent bursts then return bright sun. The same “cloudy day” percentage therefore means different portal shapes. Owners in Durban humidity should also watch soiling — salt and pollution films compound soft-sky losses until the next rain. Panel care: cleaning & care.
Self-use vs export on a soft-sky day
When production is thin, every kWh should feed the house or the battery — not drip out as export at ~153 c while you later buy evening power at 320–470 c. Check the hybrid’s “zero export” or self-use-first mode. A cloudy-day portal that shows high export usually means the battery was already full and flexible loads (geyser, dishwasher) were off — fix the schedule before you blame the weather.
Related: monthly savings · bill still high? · sizing.
Keep expectations seasonal: Highveld summers can still deliver strong midday peaks between storms; Cape winters need honest battery reserve and geyser discipline. Annual payback averages the grey weeks — do not redesign the plant after one wet fortnight.
If production collapses while neighbouring roofs look fine, check for a tripped DC isolator, dirty bottom-row modules, or a shade tree that only bites at winter sun angles — weather is not always the culprit.
Owner checklist (print this)
- Write down your goal in one sentence (bill cut, fridge backup, EV, or all three).
- Pull 12 months of kWh from bills or the prepaid app.
- List essentials circuits with approximate watts.
- Photograph the DB, roof and meter before any site visit.
- Ask every installer the same three questions and file the answers.
- Do not pay a large deposit without a written scope, model numbers and compliance line items.
Related desk pages: home solar pillar · costs & savings · all answers · FAQ.