Why is my solar controller showing 0W in daylight?

Check, in order: the PV disconnect/breaker between the panels and controller (is it on?), any inline fuses on the panel positive leads, the MC4 connections at the panels and controller, and whether the controller's display shows a fault code. A loose MC4 connector is one of the most common causes.

Why does my solar work sometimes but not others?

Intermittent charging is often partial shading (even a small shadow on part of a series string can disproportionately cut output), a loose connection that makes intermittent contact, or the battery already being full (the controller correctly stops charging at 100%). Check the controller's history/logs if it has Bluetooth monitoring.

How do I know if the problem is the panel, the controller, or the battery?

Use a multimeter: check the panel's open-circuit voltage directly at the panel in full sun (should be close to its rated Voc) — if that's correct, the panel is fine and the issue is downstream. Then check voltage at the controller's PV input terminals — if it's missing or low, the issue is in the wiring/fuses between panel and controller. If voltage reaches the controller but it's not charging, check the controller's settings and battery connection.

RV Solar Panels Not Charging? Troubleshooting Checklist

A solar array that stops charging — or never started — is one of the most common van electrical issues. Work through this checklist in order; it covers the vast majority of cases.

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1. Check the PV disconnect/breaker

If your system has a PV disconnect switch or breaker between the panels and the controller, confirm it's switched on. This is the single most common "solar isn't charging" cause after a fresh install or after working on the system.

2. Check inline fuses on the panel leads

If you have parallel strings with inline MC4 fuses, a blown fuse on one string cuts that string's contribution entirely (and can cause intermittent or low output if you have multiple strings). Pull and check each fuse.

3. Check MC4 connections

Loose or partially seated MC4 connectors — at the panels, at any extension cables, and at the controller — are a frequent cause of intermittent or zero output. Disconnect and reseat each connection, listening/feeling for the click.

4. Measure voltage with a multimeter

Work from the panel toward the battery:

At the panel terminals (in full sun, nothing connected): should read close to the panel's rated open-circuit voltage (Voc). If this is correct, the panel itself is fine.
At the controller's PV input terminals: should be similar to the panel reading. If it's missing or much lower, the issue is in the wiring or a fuse between the panel and controller.
At the controller's battery output terminals: should be close to battery voltage. If PV input is correct but there's no output, the issue is in the controller or its connection to the battery.

5. Check the controller's settings and display

If the controller has a display or Bluetooth app (e.g., Victron SmartSolar via VictronConnect), check for:

Fault codes — most controllers display a specific error.
Battery voltage setting — wrong nominal voltage (12V vs 24V) prevents proper operation.
Battery already full — the controller correctly stops/reduces charging near 100%. Check the battery monitor before assuming a fault.

Partial shading can look like a fault

A small shadow across part of a series string can disproportionately reduce the whole string's output — sometimes to near zero — due to how series strings work. If output recovers when the shadow moves, this is the cause, not a wiring fault.

6. Check the negative/ground connection

A loose or corroded negative connection from the controller to the battery negative bus bar can cause the controller to behave erratically or not charge at all, even if PV input looks correct.

Always cover panels or use the disconnect before working on wiring

Solar panels produce voltage whenever there's light, even on a cloudy day. Cover them or switch off the PV disconnect before disconnecting MC4 connectors or working on solar wiring, to avoid sparking under load.