Planning permission for the supply poles was granted in June 2008
A remote mountain village with just nine properties has mains electricity for the first time.
The National Grid said Abergeirw in Gwynedd was the last village in its network area to be fully connected.
The last of 95 poles stretching five miles (8km) was erected earlier this month, meaning residents will enjoy their first mains-powered Christmas.
Gary Evans, of ScottishPower, said constructing the supply line had thrown up "many challenges".
Mr Evans, the company's new connections manager, was due to attend an official switch-on ceremony on Friday with Meirionydd Nant Conwy MP Elfyn Llwyd, representatives from the Snowdonia National Park and Gwynedd council.
He said: "The local community and county council worked extremely hard to get the funding for this connection and I am delighted that we have been able to deliver the project in time for Christmas.
"The processes involved in designing and constructing the line threw up many challenges and we worked very closely with all the parties involved to agree the best solution."
People might think we used to live in the dark - but it wasn't like that at all
Mary Margaret Jones
Until now, residents have used unreliable diesel generators which were noisy and could not provide constant power.
It meant many were unable to rely on fridges or freezers to store food.
However resident Mary Margaret Jones said her generator ensured she and her family had everything they needed.
"People might think we used to live in the dark - but it wasn't like that at all," said Mrs Jones.
"The generator meant we had everything we needed - as long as it was running.
"We had our fridge and freezer, even a dishwasher."
"All we had to do was get the generator running, and make sure it had fuel."
The group of residents scattered along the Afon Maddach river and its remote hillsides, farmers and local inhabitants alike, came together nearly five years ago to form their energy group, and raised £100,000 between them to pay for the electricity cabling work.
But it was another two years from handing over the cash and grants totalling £176,000, before the work was complete.
Snowdonia National Park granted planning permission for the supply poles in June 2008.
Engineers had to cross some of the most "arduous" terrain in the country
Construction of the overhead power lines and nine substations began in June and was completed by the beginning of December.
As the last of the homes are finally "turned on", it has come as something of a shock to the residents of this truly remote part of Meirionnydd.
"I find myself going round turning lights off all the time," confessed Mrs Jones.
"When everything was on the generator, if you went to bed and left the light on - you knew, because the generator wouldn't switch off until everything was off.
"Now, if you leave the light on, that's it - it can be on all night and we wouldn't know, because it is quiet."
But the generator at Bryn Llin Fawr is still put to regular use, explained Mrs Jones.
"We make sure it is started and run every week, and switch over to it to make sure everything is working.
"I know we've got mains now - but if it was to go down, it's good to know we can go back to the old generator for a while."
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