 THREE years ago, Ranbir Gill decided to transform a corner of Hounslow Heath in west London. The heath had once served as a royal hunting ground, but Gill's spot had been a landfill site in the 1970s and then became a hangout for drunks.  The 47-year-old property developer came up with a plan to turn the area into a community activity centre, with landscaped grounds. The design was centred on two manmade hills built with fly ash - the grey powder that is left over when coal is burnt in power stations.  He discovered that piling coal ash on landfill stops methane - a greenhouse gas - escaping into the atmosphere.  His redevelopment plan fell through, but Gill, an engineer by training, has put his new-found knowledge to good use.  He realised that if the methane could be trapped, it could be tapped and used to produce energy. Now the 47-year-old wants to generate power at landfill sites across the country - using more of the ash from coal-fired power stations.  "Every year, Britain's coal-fired power stations produce about 6m tonnes of ash. Half goes into cinder blocks or tarmac but 3m tonnes sit in big piles behind power stations around the country. We want to put some of it to good use," Gill said.  There are 22,000 uncapped waste dumps in Britain leaking methane, according to the Environment agency. about 1,500 produce enough to worry the regulator.  as a result, Gill reckons his new business, Lichen Renewal, has a big market to tap. Success will depend on the support of the industry - Gill wants the power stations to deliver the ash to him. He thinks they will get involved if the government agrees to o 