Businesses will be asked to send central business district office workers home during heatwaves, and city residents will be offered cash to form solar panel collectives, in a desperate bid to reduce electricity demand with ageing cables predicted to fail by the summer of 2018.

Any new buyer of power company TransGrid, under the Baird government's privatisation push, faces a $430 million repair bill to build a new cable to supply electricity to inner Sydney.

Without it, the city risks blackouts that stop trains and traffic lights and paralyse business.

TransGrid will outline the problem facing the city to a meeting of stakeholders, including business groups, councils and consumer representatives on Friday.

''It is quite challenging,'' TransGrid general manager of strategy Greg Garvin said.