Nepalese villager Khinu Darai used to have to walk about five kilometres (three miles) every day to collect firewood so she could cook meals for her family.
Then two years ago, she bought a biogas plant under a government scheme to encourage villagers to convert to greener energy -- an event the 30-year-old mother of three says transformed her life.
"Biogas is a blessing for my family. These days I don't have to go into the jungle to collect wood," she told AFP outside her simple mud-brick home in the southern village of Badrahani.
"It is clean and safe, and we are healthier now as we are not breathing in smoke all the time." In all, 82 households in Badrahani have bought biogas plants at heavily subsidised rates under the scheme, which is funded by the Dutch and German governments.
Biogas is a mixture of methane and carbon dioxide produced by feeding cow dung, human waste and water into an airtight underground tank known as digester and allowing it to decompose.
Environmentalists say biogas has huge potential in Nepal, where nearly 80 per cent of the population of 27 million live in rural areas with no electricity, leaving them dependent on firewood for cooking and heating.
This means they live in smoke-filled houses, causing respiratory problems, particularly for young children, while the destruction of forests is also a major cause for concern.
Badrahani is situated on the edge of the Chitwan National Park, home to endangered species including the Royal Bengal tiger and one-horned rhino, whose habitat is threatened by villagers chopping down trees for firewood.
"Biogas has brought a green energy revolution to the country," said Prakash Lamichhane, head of research at the Biogas Sector Partnership (BSP), the government agency in charge of installing the plants.
"We have the capacity to build 1.9 million biogas plants, but we have achieved just 11 percent of our target so far. We still have a long way to go."
Over the past two decades, BSP has installed around 210,000 biogas plants at a cost of around 350 dollars each, with the government covering a third of the price.
BSP says each plant reduces the country's already low carbon emissions by around 4.7 tonnes a year.
"We are helping to reduce greenhouse gas emissions by 987,000 tonnes every year. It is helping us combat climate change," said Lamichhane, chief of the research department.
The biogas project has won plaudits as a rare environmental success in a country with one of the world's most polluted capital cities.
But BSP research and development officer Mahaboob Siddiki said it had not always proved easy to convert villagers.
"Because the gas is produced from cow dung and human waste, villagers thought it was impure, and that it would be shameful to cook food using it," said Siddiki, who has worked on the project since it began 26 years ago.
"Several times, we were chased away from some of the villages, but we never gave up," he said, calling the technology a "win-win situation" for villagers and the environment.
It is a view shared by Bibhimaya Tamang, a 45-year-old farmer from Badrahani who uses slurry -- a by-product of biogas -- to fertilize her crops, giving her higher yields and more income from the vegetables the family grows.
"Staying in a smoke-filled kitchen for hours was painful. It hurt my eyes and I used to cough a lot while cooking," she told AFP. "Using biogas has been so much better."
Sameer Thapa, coordinator of Nepal's Alternative Energy Promotion Centre (AEPC), said the country made 600,000 dollars in 2007 by trading a million tonnes of carbon emission reductions from biogas plants.
"We have huge potential to benefit from carbon trading as we lessen the use of firewood, which releases carbon dioxide into the atmosphere," said Thapa.
"Around 80,000 biogas plants are in the process of getting approval for carbon trading by next year." Thapa said the proceeds would be used to install more plants, enabling the government to increase its carbon trading capacity further.
"Many developing countries in Asia and Africa have used our expertise to promote biogas, and many others are asking for our help," said the BSP's Lamichhane.
"Nepal has always been known as the land of mountains. Now, developing countries are calling us the land of biogas."