The taxi driver didn’t hold with all that stuff about windmills and recycling. “Waste of time if you ask me.” I hadn’t. “But you have to admit, they’ve kept it going. Not bad for a bunch of hippies.”

The visitor’s first experience at the Centre for Alternative Technology in Wales is the “water-balanced” cliff railway, which climbs a 180ft slope up into the heart of the project. The seven-acre site is dedicated to demonstrating the potential of alternative technologies and lifestyles. Power comes from wind and water generation and organically grown vegetables are nurtured by the recycled waste produced by residents and visitors. Small boys can watch their personal contribution make its way through plastic tubing and into the collection bucket.

There’s a lot to do, from making waves in the tidal energy tank to exploring the transport maze; inspecting the livestock in the smallholding or getting a mole’s eye-view of life beneath the soil. Buildings are examples of what can be done with alternative materials and designs, and none more so than the Eco Cabins. These are self-contained, self-catering residential units. Each has living space and classroom facilities - but the real educational experience comes when pupils make the connection between the power they are consuming and the slowly spinning wind turbines outside.

Additional power comes from solar panels and a hydro electric generator which feed a mains circuit and a 24-volt lighting circuit. At a consumption above 23.5 volts, lights and power circuits cut out, leaving emergency light only. For teenagers this can lead to a sudden appreciation of the possibilities of the off switch - something most, apparently, haven’t encountered before.

In emergencies a diesel generator can restore the comforts of civilisation, but most groups accept the challenge and work hard to live within their means.

Val Crank takes Year 7 pupils from Newcastle Community High School to the Eco Cabins every year. “All the water we use comes from a reservoir high above the centre and is piped down to taps. The children have to carry the water to a tank which supplies the cabins. They quickly learn about avoiding waste.” Val’s groups try to manage on the available power, which can be a problem if the weather is cloudy with little wind.

“We ran out one year,” she says, “but generally they manage very well. You can see the windmill and the solar panel output. There are no excuses - it’s down to them.”

Throughout the week everything is recycled. Cans are crushed, glass is saved and waste food is fed to the pigs. Val thinks that the cabins offer a “brilliant experience”, so brilliant in fact that Newcastle teachers take a staff-only trip to the centre earlier in the year.

This summer the centre is running a sustainable science project which promises to offer an insight into the way the planet works. “Sustainability is going to be the major force which shapes our world,” says CAT’s project director Paul Allen. “This project offers children a chance to explore the science which lies behind it.”

Aimed at 5-11s, the project will run during the school holidays alongside the centre’s usual programme of activities and displays.

The centre has come a long way from the collection of tents and huts which began the project in the early Seventies. For 1999 the site has been declared best holiday attraction and best environmental attraction in Wales, and beyond the public side the team of environmentalists are involved in government-funded research into materials and techniques which could determine how successfully we face the future.

Centre for Alternative Technology, Machynlleth, mid Wales. Tel: 01654 703743. Day trips or residential visitsdiscounts for school parties