The winning Green Valleys team with contest judge Lord Puttnam
A group of 21 small communities has scooped £300,000 after winning a major environmental competition to cut carbon emissions.
The Brecon Beacons-based Green Valleys Project, one of three joint winners, was up against more than 350 other schemes in the Big Green Challenge.
Judges praised Green Valleys for the way it had cut carbon emissions by building 10 hydroelectric systems.
Event organisers said the Green Valleys team had "exceeded our expectations".
The Beacons project, made up of 21 small communities, plans to invest the prize money in other micro-hydroelectric schemes.
One of the other joint winners was Shropshire-based Household Energy Service, which offers a free environmental survey for households in Shropshire and a small part of Powys.
Grenville Ham, the founder of Green Valleys and an officer at Brecon Beacons National Park Authority, said the idea for the project was dreamed up over a pint in a pub.
"I am relieved - it's been a phenomenal effort and a great acknowledgement for the belief we've had in ourselves," added Mr Ham.
"We plan to use the money to invest in local hydro electric schemes, roll them out throughout the Brecon Beacons and make the area carbon negative.
"The team work has been phenomenal. When you think the two-year programme started with two blokes sitting in a pub, and now we've won a top UK environmental prize."
The Big Green Challenge is run by the National Endowment for Science, Technology and Arts (Nesta).
The aim of the competition was to cut carbon emissions and promote sustainability.
The final was the culmination of a two-year programme to encourage community groups in the UK to do their bit for the environment.
Jonathan Kestenbaum, Nesta's chief executive, said: "The Green Valleys team has exceeded our expectations of what communities can achieve in reducing carbon emissions and for this they should be congratulated.
"The success of the project proves that when communities are incentivised, empowered and supported they become a compelling force in solving some of society's biggest challenges."
Wales' Environment Minister Jane Davidson said she was delighted the effort and dedication shown by the Green Valleys Project had been recognised.
"Whilst many leaders are still talking about how to tackle climate change, the Green Valleys project is leading by example," she added.
In 2008, 355 groups came forward with a range of ideas aimed at reducing CO2 emissions in their communities.
Nesta selected 100 of the most promising ideas and chose 10 finalists, which included the Green Valleys Project - the only one from Wales.
Llangattock, one of the 21 communities involved in the Green Valleys Project, scooped £140,000 in November after winning a challenge set by British Gas to cut energy consumption.