Why does my solar inverter overload when the geyser starts in South Africa?

Answer first: Check whether the geyser sits on the backup/essentials board, what element kW it is (often 2–4 kW), and what else was running when the fault logged. Then decide: move geyser off backup, diversify with a timer/sun schedule, or replace with a heat-pump on a planned circuit.

What the inverter is protecting

• Continuous AC output rating vs surge/peak windows.
• Battery discharge power limit (a 5 kW hybrid with a small pack can still trip on power, not only energy).
• Passthrough / grid-assist rules when the grid is present vs islanded in Stage.

Related: geyser on backup · essentials board · inverter size · fault codes.

Quick homeowner tests

1. Note the exact fault code and whether the grid was on.
2. Retry with geyser breaker off — does the overload vanish?
3. Check app loads at the moment of trip (stove, kettle, EV, pool).
4. Confirm element rating on the geyser nameplate.

Remedies that usually work

• Timer / PV diversion: heat water in sun hours on non-backup or when passthrough is healthy — self-use scheduling.
• Heat-pump geyser: far lower running kW for similar hot water — check payback — heat-pump vs geyser · water heating hub.
• Move geyser off essentials: keep lights/fridge through Stage; accept cold water during shedding.
• Staged loads: never coincide oven + geyser + kettle on backup — stove / oven.
• Right-size hybrid / battery power: only after load truth — replacement cost.

Induction, pool and borehole cousins

Same overload story appears with induction hobs, pool pumps and borehole motors — surge + continuous watts. Plan diversity before the next DB change — induction · pool pump · borehole.

Savings angle

A geyser that forces grid import every morning on a high TOU block burns the solar business case. Shifting or heat-pumping that load often beats buying export-centric extra panels — self-use · Cape Town TOU.

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.

Passthrough vs island behaviour

With a healthy grid, many hybrids passthrough geyser loads up to the main breaker. In Stage island mode, only inverter+battery power remains — that is when overloads appear. If trips only happen during shedding, the design failed the backup brief, not the sunny-day brief — solar during shedding · changeover / ATS.

Element size reality check

A 4 kW element on a 5 kW hybrid leaves 1 kW for everything else in island mode. Fridge start surges and a kettle will still win. Measure or read the nameplate; do not assume “geyser = 2 kW”.

Heat-pump electrical notes

Heat-pumps draw less continuous power but can surge on compressor start. Confirm soft-start options and whether the unit stays on backup. Payback vs resistive still depends on tariff and hot-water kWh — whole-home heat-pump path · install order.

DB labelling after the fix

If you move the geyser off essentials, update labels and the handover load list so the next technician does not “helpfully” move it back. Dual-supply and essentials labels matter for CoC — dual-supply labels · CoC · inspector tips.

When replacement is justified

Replace or upsize the hybrid only after load truth: measured essentials, geyser plan, EV diversity, and Stage goals. Buying 8 kW to run a wasteful 4 kW element all evening is an expensive way to heat water — replacement cost · hybrid brands.

Logbook template after each trip

1. Date/time and Stage level (if any).
2. Fault code verbatim from the app/display.
3. Which breakers were on (geyser, stove, kettle, EV).
4. Battery SoC and ambient temperature.
5. Whether the grid LED showed island or grid-tied.

Three logged events give an electrician a pattern; one angry WhatsApp does not — fault codes · monitoring.

Diversify hot water, do not only upsize silicon

Timers, smaller elements, heat-pumps, and solar thermal where appropriate often beat a pure inverter upsize. If you already planned a heat-pump, stop putting the resistive geyser on backup “temporarily” — temporary becomes permanent — water heating · payback.

Three-phase homes

Balance geyser and stove across phases. A single-phase hybrid on a three-phase DB can look fine until one phase carries the entire hot-water hit — single vs three-phase · inverter sizing.

Quote language to demand

“Geyser on non-essential” or “geyser on essential with X kW headroom proven” must appear in writing with the measured board list. Vague “whole house backup” marketing is where overload tickets are born — read a quote · red flags · check a quote.

EV and geyser on the same evening

A wallbox at 7 kW plus a 3 kW element is a classic island-mode disaster. Schedule EV charging for sun hours or post-Stage, and keep the geyser off backup if the hybrid cannot prove headroom. Load-management features on quality wallboxes help only when configured — EV load management · EV from solar · charger cost.

Generator assist myth

Adding a noisy genset to “cover the geyser” without interlock design creates backfeed risks. Fix the board and hot-water plan first; only then discuss generator input modes — generator interlock · diesel cost.

After the permanent fix

Update the essentials list, SoC policy, and insurance description. Retest one Stage simulation with the new board layout. File photos next to the CoC — SoC settings · essentials · insurance.

Summary decision tree

1. Confirm geyser kW and whether it sits on backup.
2. If overload only in Stage → redesign essentials or move geyser off backup.
3. If overload even grid-tied → check passthrough limits, main breaker and competing loads.
4. Prefer timer / heat-pump / diversity before blind inverter upsize.
5. Document the final board list and retest.

Keep this page beside geyser on backup, heat-pump payback, and SoC settings when you argue with a quote that promises “whole-house backup including geyser and stove” on a small hybrid. Related: stove · induction · check a quote.

Finally, teach everyone in the house which breakers are essentials-only. A guest who switches the geyser onto backup “just this once” during Stage recreates the overload you just paid to eliminate. Label clearly and keep a one-page house rule near the DB — dual-supply labels · essentials.

Why the element wins the fight

A 2–3 kW geyser element plus fridge surge and a kettle can exceed a 5 kW hybrid’s continuous rating even if the sticker “looks fine.” Overload trips mid-shower are a board-design problem, not a brand curse — geyser on backup · inverter size · essentials.

Fixes ranked by honesty

1. Move the geyser off backup; heat on cheap daytime solar or a timer.
2. Swap to a heat-pump with lower running watts — heat-pump vs geyser.
3. Upsize hybrid / split phases if coincidence peaks are permanent — phases · NMD.

Soft-start myths

Some elements and controllers reduce inrush; verify with a clamp meter at commissioning rather than trusting a brochure line. Related: fault codes · read a quote.

Derated continuous rating is the real ceiling

If Highveld altitude already trimmed continuous kW, a geyser start has even less headroom — size from derated continuous, not brochure surge — Highveld derate · inverter size · heat pump add.

Measure first — then size — then buy

Clamp the evening essentials, log a week of bill data, and only then accept a bill of materials. Quotes written from a sales average miss your house. Bring the measurement sheet to every installer meeting.

When the quote ignores your numbers, discard it.

Quick questions

Can soft-start fix a geyser overload?

Resistive elements do not soft-start like motors. Timers, board design or heat-pumps are the usual levers.

Is a 8 kW inverter enough for a 3 kW geyser?

Only when little else runs on that output and the battery can feed it in island mode. Add stove or kettle and the maths fails.

Should the geyser be on backup at all?

Only if hot water during Stage is a stated priority and the hybrid was sized for it. Many homes keep geysers off-backup on purpose.

Sources & related

• Solar News 24 — geyser on backup
• Solar News 24 — heat-pump vs geyser
• Solar News 24 — inverter fault codes