A spokesperson said the vehicles had been ready to enter service in November last year, but the main infrastructure contractor had gone into administration.
Five diesel powered generators were being used to charge 20 electric buses until there was a permanent electrical connection, they added.
The company said the arrangement still delivered environmental benefits because the electric fleet vehicles produced zero tailpipe emissions when in service.
A spokesperson from East Yorkshire Buses said: “Due to unexpected and significant delays in commissioning the electrical supply we took the decision to power the charging points in the short term with generators allowing us to remove older diesel buses from our fleet.
“The use of the generators is only ever a short-term measure and we expect the power supply to be commissioned in the coming few weeks.”
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