An extra 36,000 solar panels have been added to the ACT's first "solar highway", with the completion of the Williamsdale solar farm on Friday.

There are now four solar farms by the side of the road that stretches down Canberra's eastern side, from the Majura Parkway to the Monaro Highway: Mt Majura, Mugga Lane, Royalla and Williamsdale.

ACT climate change minister Shane Rattenbury said the "solar highway extension" will "substantially boost" efforts to reduce green house gas emissions.

"The facility will generate 21,900 megawatt-hours of renewable electricity each year, enough to power around 3000 Canberra homes," Mr Rattenbury said.

Williamsdale was the last of the three projects from the ACT's large-scale solar auction to be completed.

But Mr Rattenbury was unable to say whether any more renewable energy auctions were on the cards

"The ACT government has secured contracts to provide 100 per cent of the ACT's electricity from renewable sources. I am pleased that we are on track to meet our 100 per cent renewable electricity target by 2020 and to become a zero emission jurisdiction by 2050," Mr Rattenbury said.

"There is a potential that, pending further approval, should there be substantial population growth in the future (and greater electricity consumption), further auctions may be used to secure more renewable energy generation."