Dublin Bus is to add 100 new hybrid buses to its fleet later this year.
The double deckers can run in zero emission mode for at least 2.5 kilometres.
The National Transport Authority is planning to order up to 600 of the buses over the next five years.
The Enviro400ER models are being made by one of the world's largest bus manufacturers.
ADL said it was chosen because it "provided the most economically advantageous offer".
The first 100 buses have been firmly ordered and are to be delivered in autumn 2020.
Some of the buses will run on Bus Eireann city services.
The Enviro400ER switches off its diesel engine at low speeds, during approach to and departure from stops, and when stationary.
The 11 metre long buses will seat 66 passengers, with separate spaces for wheelchair users and buggies.
Colin Robertson, CEO of ADL, said the buses "will reduce emissions and passengers will love the smooth journey experience".
"Drivers are bound to enjoy a great working environment in its spacious cab", he added.
