Tucked away in a wooded valley in west Wales, not far from the historic town of Machynlleth, lies one of the power-houses of the movement for sustainable development and `green' technology.

The Centre for Alternative Technology (CAT) first opened its doors to the public in September 1975. In the booklet Crazy Idealists: the history of CAT(*), written to mark its 25th anniversary, the founders recall the days when they first colonized the disused and overgrown Llwyngwern quarry. They, as well as their theories and technology, were then regarded as unarguably `alternative'.

It was the ready availability of water as a source of instant renewable energy that made the quarry particularly attractive to the pioneers. Today, appropriately enough, the seven-acre centre is reached up a steep cliff face by a water-balanced railway which uses little energy. The centre is now so awash with self-produced `renewable' electricity--from hydro turbines, wind turbines, solar (photovoltaic) panels and wood chip burners--that it sells the excess to the national grid. The site also boasts a flourishing organic garden, demonstrations of innovative composting combinations and ecological sewage disposal methods.

Over the years the emphasis has moved away from experimenting with a self-sufficient lifestyle to catering for the ever-increasing demand for `know-how' on sustainable technology. `We get around 12-13,000 enquiries a year,' says Phil Horton, Technical Information Officer. He came to the centre from being a systems engineer with the BBC. Job satisfaction must count for a lot as salaries are not high and all members of the 36-strong cooperative receive the same amount, whatever their qualification and whatever job they do. Besides cooperative members, there are 14 other full-time staff as well as casual staff in the busy summer months.

CAT receives more than 80,000 visitors a year, making it the largest tourist attraction in that part of Wales. School parties account for a high proportion of the visitors. There is a full education service including residential as well as day visits, training for teachers and material tailored for the needs of various stages of the National Curriculum. There is accommodation for 36 in two specially-designed `Eco Cabins'.

The latest addition to the site is the `sustainably built' Autonomous Environmental Information Centre. Like most things at CAT it serves more than one purpose. It houses the book shop and information room (where you can explore its award-winning web site--www.cat.org.uk). And it is also `a test bed for ecological building techniques'. A lime-based concrete was used for the foundations, which avoided using cement. The roof is supported by walls made of rammed earth, and low grade sheep's wool has been used for insulation. There are copious areas of glass, to let in as much natural light as possible, and a huge solar panel on the roof, all framed by locally-hewn wood.

`The cutting edge for ecologically sustainable technologies is now in integrating the different elements,' Marketing Officer Steve Jones told me. `It's this "joined-up thinking" that gives me a buzz.' He instanced CAT's heat main which links a wood chip burner with the information centre's solar water heater. This produces enough heat to be circulated to each of the site's seven major buildings. Crucially this includes the kitchen which serves the vegetarian (everything organically grown) restaurant. Another beneficiary of this `heat trading' is the Straw Bale Theatre, the walls of which are made entirely of straw bales, protected by a light lime covering.

CAT was called in to advise (on matters ranging from buildings to power provision and sewerage) those who volunteered for the year-long BBC programme Castaway 2000. This records the efforts of a community of 30 to survive on a deserted Scottish island. Indeed, so mainstream has CAT become that consultancies have included Amoco (UK) Ltd and British Rail. From the centre's Buy Green mail order catalogue you can order an amazing variety of items, including a solar fan cap, rustic pencils and a solar cook book.

There is no doubting the interest, both in Britain and overseas, in what CAT has to offer. `We are witnessing the most rapid growth in demand for information on green technologies we have ever known,' says Development Director Paul Allen. `This has extended our role beyond a research centre, or even a demonstration centre. We are now a large scale clearing-house for vast amounts of practical information, contacts and advice, often acting as first port of call for those beginning a search.'

Assessing the role of the centre over 25 years, Paul Holden, Director of the Soil Association (the UK charity which researches and promotes organic farming), says CAT has helped to reshape the attitudes of an entire generation. `To take action we need to be inspired and empowered,' he says. `That has been the greatest contribution of CAT. The centre has enabled countless individuals to take big ideas, simplify them and give them a practical application in our daily lives.'