Quick answer Safety first The diagnosis order The six checks What lightning does Prevention FAQ
Quick answer
Post-storm solar failures are usually boring, in this order: a tripped DC breaker or blown fuse, a charge controller latched in a fault state after a surge, water in a connector or junction box, then — much further down — panel damage and battery problems. A multimeter and this six-step order find the overwhelming majority of causes in under an hour. The rule that saves money: diagnose before buying — the most expensive post-storm mistake is replacing a controller that just needs its breaker reset, or a panel that just needs its connector dried and re-seated.
Safety first: wet electricity deserves respect
Before touching anything: if the roof or array is wet and anything smells burnt or is visibly arcing, stop — that is a job for someone qualified. Working assumptions for the rest of this page: you are probing a low-voltage DC system (12–48V bank class) with dry hands, from the ground where possible. Cover panels with an opaque blanket or cardboard before disconnecting anything — a lit panel is always a live panel (the testing safety framing). And never disconnect a battery cable with a load running — spark plus hydrogen is how lead-acid banks become stories.
The diagnosis order
Work cheapest-first, exactly in this order. Each step either finds the fault or eliminates the cheapest class of causes before you touch anything expensive:
| Order | Check | Tool | What it means |
|---|---|---|---|
| 1 | Breakers, fuses, disconnects | eyes | The #1 post-storm cause is a protection device that did its job |
| 2 | Controller state and voltages | multimeter | Surge-faulted or latched controllers mimic dead arrays |
| 3 | Battery voltage and health | multimeter | A bank dragged low makes the whole system misbehave |
| 4 | Panel Voc in daylight | multimeter | Separates panel damage from everything upstream |
| 5 | Connectors and junction boxes | eyes + meter | Water ingress corrodes quietly and kills current |
| 6 | String wiring | multimeter | The deepest check — the full procedure |
The six checks in detail
1. Breakers, fuses, disconnects. Every properly built system has a DC disconnect or breaker between array and controller, and fuses on parallel strings (what belongs where). After a storm, check each one. A tripped breaker after lightning is not a failure — it is the system working. Reset once; if it trips again immediately, stop and go to step 2 with the meter, because something downstream is genuinely faulted.
Checks 2 through 6 of the diagnosis order: battery resting voltage, controller input and output, panel open-circuit voltage, and continuity through weathered connectors. A 600V CAT III rating covers hobby-scale DC safely (per manufacturer spec). Not for: residential string-system combiner interiors — licensed-electrician territory. The honest tradeoff: no Bluetooth logging — you write the readings down, which in a diagnosis is a feature; the notebook is the record.
Check price on Amazon (opens in a new tab) Price & availability shown on Amazon.com — we may earn a commission.2. Controller state. A nearby strike induces surges that can latch a controller into a fault state without destroying it. Symptoms: error codes, dead display, or input present but no charging. The meter sequence: panel-side voltage present at the controller’s PV input? Battery-side voltage present? If both read sane but charging current is zero, power-cycle the controller (disconnect PV first, then battery, wait, reconnect battery then PV — check your manual’s order). If it faults again, the controller took the hit protecting the bank — that is what it was designed to do, and the controller classes are compared here when you replace it.
3. Battery voltage. A storm usually means a dark day or three; the bank may simply be low, and low-voltage cutoffs make systems look dead. Measure resting voltage (nothing charging, loads off): a 12V lead-acid bank near 12.0V or a lithium bank at its BMS cutoff explains everything. Recharge gently and re-test — and if the bank sat flat through freezing weather, read the cold-chemistry page before charging a lithium bank.
4. Panel Voc. Daylight, panels disconnected, meter on DC volts: a healthy 12V-nominal panel reads near its label Voc (the full procedure). Hail or debris damage shows as healthy-looking glass but collapsed voltage — and the salvage triage table classifies exactly what’s worth keeping.
5. Connectors and junction boxes. Driven rain finds every connector that was never properly mated. Signs: green corrosion, water tracks, or a connector that reads voltage but delivers no current. Dry, clean, re-crimp or replace with proper MC4 tooling and technique, and re-seal the entry. If a string fuse blew here, replace it with the same rating — never higher:
Post-storm string-fuse replacements sized to the common 100W-class parallel string (per manufacturer spec) — same rating as what blew, which is the only correct rating. Not for: the battery-side main fuse; that's a Class-T/ANL conversation. The honest tradeoff: keep the spares with the tools, because the fuse that blows is always the size you didn't pack.
Check price on Amazon (opens in a new tab) Price & availability shown on Amazon.com — we may earn a commission.6. String wiring. Last because it’s deepest: the full diagnostic walks string voltage and current math per string. A single dead string in a multi-string array often changes nothing you’d notice without the meter — which is exactly why the storm is when you find it.
What lightning actually does to a system
Direct strikes destroy whatever they hit — no residential protection survives one. What protection does handle is the common case: induced surges from nearby strikes, which ride long wires into controllers and inverters. That is why grounding and surge protection is the boring page that saves the expensive box: SPDs at the combiner and controller, short straight ground conductors, one bond point. If this storm took out a controller and the system had no surge protection, the replacement budget should include the SPD, not just the controller.
Prevention before the next storm
In order of value: (1) Surge protection and grounding audit — one afternoon. (2) Connector mating check — every MC4 clicked to its detent, every junction box gasketed. (3) A winterizing pass before storm season covers the cold-weather failure modes. (4) Spares: one fuse kit, one spare controller if the system is your only power — the grid-down spares thinking applies to storm kits as much as anything else. And the complete grid-down guide frames all of it in one system view.