Public buses fitted with ultra-thin solar panels started plying the roads here yesterday in a six-month proof-of-concept trial by bus operator Go-Ahead Singapore.

This is the first time such solar panels, which are 1.6mm thick, flexible and shatterproof, have been installed on buses in Singapore.

They were installed on the roof of two Man A22 Euro 6 diesel-powered buses. The buses will be used on service 15, which starts and ends at Pasir Ris Bus Interchange, in a trial that runs until September.

Weighing less than 20kg, the solar panels will supply 1,000 watts of power. This will be used to charge the battery on the buses, which would otherwise have to rely on the vehicle's alternator. This will in turn reduce the load on the engine.

The bus battery is typically used for ignition and to power components like lights and security cameras when the engine is turned off.

The panels are expected to help Go-Ahead Singapore save 1,400 litres of diesel per bus per year.

This is about 3 to 4 per cent of the fuel that is typically consumed by such diesel buses, and translates to a reduction of 3.7 tonnes of carbon emissions per bus per year.

These figures are based on data from a similar trial that Go-Ahead Singapore's parent company has been conducting since 2019 in Southampton in the United Kingdom, where there are currently 18 buses fitted with these solar panels.

The six-month trial here aims to evaluate how effective the panels are in harnessing solar energy here and to ensure the panels can withstand the higher temperatures and daily washing of the buses.

The solar panel efficiency is expected to be higher in tropical Singapore, said Go-Ahead Singapore managing director Andrew Thompson.

He said: "If we see the sort of savings and benefits that we expect, then we would certainly be looking to fit them on more buses, including electric buses as well.

"A lot of the diesel buses in Singapore have still got many years of life left in them. By fitting the solar panels, we can make the diesel buses even more green and efficient."

The cost of the panels is expected to be recouped from savings resulting from the reduction in fuel consumption after four years.

In a Facebook post, Transport Minister Ong Ye Kung said the trial is "another small step towards a greener public transport system".

The Government has committed to phasing out and replacing all diesel buses with electric buses or diesel-electric hybrids by 2040.

Go-Ahead Singapore said the two buses with solar panels underwent rigorous safety assessments by the Land Transport Authority and are approved for public road trials.

The panels, which are at least three times thinner than some conventional solar panels, will be inspected weekly in the first two months. The operator will then do a review to determine the appropriate inspection schedule.

Said its engineering director Leonard Lee: "Typically, solar panels are big and very heavy." So there will be concerns if they are installed on top of the bus.

"The ones that we use are ultra-thin and very lightweight. So, we have no issues in this aspect."