A street light that worked last week and is dark tonight is rarely a total loss. In most cases one component has failed — battery, controller, panel or lamp head — and the others are fine. The trick is to test in the right order instead of replacing parts at random.
Start with the symptom
| What you see | Most likely cause |
|---|---|
| Completely dark, night after night | Battery or controller failure |
| Works for a few nights, then dark | Battery deeply discharged — long rain spell or under-sized panel |
| Lights up but very dim | Battery aged; capacity below roughly half of rated |
| Comes on and off at random | Loose terminal or poor controller contact |
Write the symptom down before touching anything. It narrows the fault faster than any instrument.
Test 1 — Panel voltage (daylight)
Measure the open-circuit voltage at the panel leads with a multimeter, in direct sun. A healthy 18 V nominal panel reads about 18–22 V. A reading near 0 V means the panel has failed or the leads are broken; a reading well below spec in full sun points to a cracked cell or heavy shading.
Test 2 — Battery voltage
Disconnect the battery and measure it after a few minutes of rest:
- 12 V system: healthy is above 12.6 V; below 11 V means deeply discharged or failed.
- 24 V system: healthy is above 25.2 V; below 22 V is the same diagnosis.
If the voltage recovers after a full sunny day and then collapses again within two nights, the battery has reached the end of its service life.
Test 3 — Controller indicator
Most controllers signal state with an LED: charging, battery full, or fault. A blinking fault light with correct panel and battery voltages means the controller itself is the problem. Photograph the indicator pattern — it identifies the fault code for the supplier.
Test 4 — Bypass the controller
With the panel disconnected, connect the lamp head directly to a charged battery of the correct voltage for a few seconds. If the lamp lights, the controller is faulty and the lamp is fine. If it stays dark, the lamp head or its driver has failed.
Keep this test short and never connect a lamp to a voltage above its rating — it converts a repairable fault into a scrap luminaire.
Fault, cause, fix
| Fault | Cause | What to do |
|---|---|---|
| Battery discharged | Rain spell longer than the designed autonomy | Allow 2–3 sunny days to recover; if it repeats, increase panel or battery capacity |
| Battery aged | Lead-acid after 2–3 years, LiFePO4 after 5–8 years | Replace with the same chemistry and capacity |
| Controller failed | Moisture, surge, over-discharge | Replace with the same model; observe wiring order |
| Panel failed | Impact damage, ageing, broken lead | Replace with the same wattage and voltage |
| Lamp head failed | LED or driver failure | Replace the head or the driver module |
| Intermittent | Loose terminal, corroded joint | Clean and re-torque; add dielectric grease |
Why lights fail after a rainy spell
Autonomy is designed for a stated number of consecutive rainy days. When the weather exceeds it, the battery runs flat and the controller's low-voltage cut-off keeps the lamp dark even after the sun returns — until the battery recharges enough. If this happens every wet season, the system was configured for 3 days in a 7-day climate, and the fix is capacity, not parts.
Five habits that prevent most failures
- Clean the panel once or twice a year — dust alone can cut generation by around 30%.
- Check terminal tightness annually; most intermittent faults start here.
- Specify LiFePO4 rather than lead-acid — roughly two to three times the service life.
- Keep trees and new buildings from shading the panel; shading is a design error that no component upgrade fixes.
- Record commissioning data (panel voltage, battery voltage, settings) so future comparisons have a baseline.
Warranty and spares
Lamp heads, batteries, controllers and panels are all replaceable individually — the fixture rarely needs to be scrapped. Under warranty, photograph the controller indicator and the multimeter readings; that is usually enough for the factory to ship the right part without a site visit.