Hardware

What is MPPT string mismatch on a home solar inverter in South Africa?

Mismatch happens when paralleled strings differ in current or when mixed orientations/shade feed one MPPT — yield drops and inverters may derate; design equal strings or separate MPPTs per orientation.

Updated 27 October 2026 · Illustrative ranges — not a formal quote, credit decision or legal advice.

Answer first: Give the designer roof photos with orientations and shade. Equal string lengths on one MPPT; different faces on different MPPTs when the inverter allows — MPPT · shade / optimisers · string vs micro · cold Voc.

Mismatch symptoms

Symptom	Likely cause
One string always low	Shade, soiling, or bad MC4
Noon clip on one MPPT	Overcurrent / design error
Winter isolator trips	Voc too high for cold days

MC4 · soiling / dust · monitoring.

Desk close

Keep metro and OEM PDFs beside this page. When rand bands disagree with a live primary, the primary wins — metro tariffs · tariffs 2026 · choose installer · get quotes · check a quote.

Sources homeowners can open

Your metro SSEG / tariff PDF (live municipal site).
OEM inverter and battery installation + warranty PDFs for the quoted SKUs.
NERSA and municipal tariff schedules for the current year.
SANS / NRS notes via your registered electrician (earthing, dual-supply, grid interface).

Commissioning evidence pack

Serial photos, firmware version, export-limit screenshot, CT polarity photo, dual-supply labels, CoC number, guest monitoring login — with the invoice PDF — CoC · export limit · CT clamps · labels · firmware.

Tariff and fixed-charge reminder

Fixed charges remain after panels go up — fixed charges · monthly savings · export vs self-use · bill still high · costs & savings.

Safety do-not list

Do not DIY dual-supply boards, earthing, or MC4 strings.
Do not bridge RCDs or defeat BMS protections.
Do not ignore isolation or earth-fault alarms.
Do not disable export limits or grid-interface settings.

DIY risks · earth leakage · MC4 · DC isolation · red flags.

Stage-weekend reality check

Essentials first through your worst Stage window — essentials · Stage strategy · Stage 4 · SoC · load shedding hub.

Extra SA context 1

Keep this page next to your metro tariff PDF and the OEM warranty letter for the SKUs on your quote. When numbers disagree, the live primary wins. After any Stage-calendar change, revisit SoC floors and the essential board list — SoC · Stage strategy · Stage 4 · essentials · monitoring · choose installer · get quotes · check a quote · FAQ · about.

Extra SA context 2

Extra SA context 3

Extra SA context 4

Extra SA context 5

Extra SA context 6

Extra SA context note 2

Keep metro and OEM PDFs beside this page. When rand bands disagree with a live primary, the primary wins. Revisit SoC and essentials after any Stage-calendar change — SoC · Stage strategy · Stage 4 · essentials · monitoring · choose installer · get quotes · check a quote · FAQ · about · costs & savings.

Extra SA context note 2

Homeowner action list

Match quote SKUs to installed serial photos.
Confirm export setpoint and CT polarity in the handover pack.
Put fibre/router on essentials so monitoring and clocks survive Stage.
File CoC, dual-supply photos and guest login with the invoice PDF.

CoC · export limit · CT clamps · fibre backup · labels · check a quote · get quotes.

Bill maths before hardware

Pull three months of kWh and rand from your bill or prepaid tokens. Compare that to the quote’s self-use assumption at your metro’s published rates — monthly savings · fixed charges · export vs self-use · export credit vs self-use rand · metro tariffs · costs & savings · check a quote.

Mismatch that quietly steals Highveld yield

Mixing panel wattages, orientations or shade patterns on one MPPT forces the weak string to drag the strong. Prefer one orientation per MPPT, matched Imp/Vmp, and separate east/west where the inverter allows. After any roof change, re-check string Voc on a cold morning against the inverter max.

Record Voc/Isc at commissioning for each string.
Optimisers/microinverters only where shade is proven — not as default upsell.
shade options · cold Voc · east-west.

Homeowner close-out for mppt string mismatch sa

Keep OEM and metro PDFs beside this answer. Confirm Incl. VAT line items, NRS-listed SKUs where relevant, and who owns paperwork after deposit. Compare two written scopes before you pay — read a quote · choose installer · check a quote · get quotes · costs & savings · metro tariffs.

Quick questions

Can I mix panel wattages?

Avoid on one MPPT — keep Voc/Isc families aligned.

East-west on one MPPT?

Often poor — prefer separate MPPTs or accept loss.

Shade on one panel?

Hurts the string; consider redesign or optimisers where justified.

Winter Voc?

Cold mornings raise Voc — string length must still fit inverter max.