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Solved problems · Electrical · Crew answer

Why isn't my solar panel charging the batteries?

When solar output drops to zero or near it, check the controller's status first, then panel voltage, shading, connectors and fuses. Most faults are wiring, settings or shade.

Symptom

The solar charge controller shows little or no charge current in good sun, the batteries aren't topping up at anchor, or the controller display or app reports an error or 'off'.

Likely cause

An MPPT controller only charges when panel voltage is high enough above battery voltage. Victron's SmartSolar manual, for example, needs PV at least 5 V above the battery to start. No PV at the controller means an open circuit: a blown fuse or breaker, a corroded or unplugged MC4 connector, or a broken cable at a deck gland or arch. Partial shade from a boom, sail or mast can collapse output. Wrong battery settings, a full battery, or a BMS or remote signal disabling the controller also stop charging.

Stop now if

A connector, cable or the controller is hot, melted or smells burned, or you see damage to a panel. Disconnect the battery side and PV side as the controller manual directs and get help. Panels make voltage whenever light hits them, so cover them before working on PV wiring.

The fix, in short

  1. Read the controller status. Check the display or app for a charge state, error code or 'disabled' message. Victron publishes a full list of MPPT error codes, and many have a simple cause.

  2. Measure PV voltage at the controller. In sun, measure voltage on the PV terminals. Compare it to the battery voltage and the panel's open-circuit rating. Zero or very low readings point to the panel wiring, not the controller.

  3. Check shade and the panels. Look for shadows from the boom, mast, radar or rigging. Even a strip of shade across one cell can cut output sharply on some panels.

  4. Inspect connectors, fuses and breakers. Cover the panels first. Then check MC4 connectors, deck glands, fuses and breakers for corrosion, heat damage or loose pins.

  5. Check battery settings and full charge. Make sure the battery type and charge voltages match the batteries. A controller that shows float or very low current may simply have a full battery.

  6. Check the battery-side wiring. Long or thin battery cables or a loose battery terminal can make the controller see a false voltage and stop charging early. Measure voltage at the controller and at the battery while charging.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Solar charging: Solar panels, MC4 connectors, PV fuses or breakers, MPPT or PWM charge controller
  • Batteries: House bank

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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