While the fault is blamed on overcast skies in the past couple of days, depriving sunlight for battery recharge, some of these units have been crippled by a “system failure”.

On Sunday evening, dozens of solar lamps failed to light up while some of them were dim. The malfunction of the charge controller, which regulates the charge to be stored on the battery, has also been reported.

Nutan Dev Bhattarai, project manager at the Nepal Electricity Authority, said it was a minor problem and could be fixed promptly.

With a full charge, a unit can function up to 12 hours. Each set is equipped with a 40-watt LED light and 130-watt solar panel which can be charged up in seven hours of adequate sunlight. With mere daylight, 15 percent charging is possible. If proper care and maintenance is ensured, technicians said earlier that the technology could last over ten years. Enhanced technology dims down the lights automatically when it senses daylight.

According to Ram Prasad Dhital, an expert on solar technology who heads the Alternative Energy Promotion Centre, a unit is unlikely to malfunction in such a short period of time. “Either the unit has to be very low quality, or it’s the gloomy days,” he said.

Regular maintenance is necessary, as dust can blanket solar panels, curtailing their energy absorbing capacity, Dhital added. Most companies provide warranty on the units, which enables parts replacements.

The lights last a minimum of 50,000 hours. Each LED bulb receptacle comes with its own power backup system and solar panel for ease of maintenance and functionality. “The charge controller and battery are sealed and made weather proof,” said Dhital. If the charge is inadequate and the battery is always fully discharged, the life of the cell can decrease.

Besides major roads, the solar lights installed at Patan Durbar Square have started malfunctioning. Over 1,000 solar lamps were installed in Kathmandu Valley in the past few months.