Kowloon Motor Bus said 2,000 of its buses, or about half of its fleet, could be partly powered by solar energy by the end of this year.

The franchised bus operator said it has been installing thin-film solar cells on bus roofs, generating electricity to ignite the engine and power all electrical systems on board.

KMB said it has installed solar cells on around 1,300 buses so far.

Carmen Ng, deputy head of corporate communications at KMB, said each solar-powered bus will save five percent of fuel a day and reduce six tonnes of carbon emission per year.

Ng said the system comes in especially handy in the summer because it can cool down vehicles.

"When the engine of the solar bus is turned off and the temperature inside is over 35 degrees Celsius, the solar-powered ventilation system will activate to extract hot air from the bus, thereby effectively reducing the temperature by around eight to 10 degrees Celsius," she said.

Ng added that this is the first time KMB has adopted the renewable energy system extensively after testing its previous versions with prototypes since 2017.

The company plans to have solar cells fitted on all double-deckers by 2040.