J eremy Leggett, earth scientist and campaigner, is an optimist. He sees a sunlit future. He sees sunlight crashing onto rooftiles which look quite like tiles but which are really just sheets of amorphous silicon backed by stainless steel: every one a photovoltaic cell.
A photon of light - whether from direct sunlight or reflected off clouds - still packs a punch. It can slam into the amorphous silicon to be converted by the magic of modern physics directly into electric current where it flows into the wiring, keeps the freezer at -15 C, chills the Chardonnay in the fridge, powers the domestic appliances and still leaves him spare current to sell to the electricity board and help the national grid.
On average, the sunshine that hits the earth has enough energy every square metre to run an electric hairdryer. Capturing that energy is a problem. Plants use photosynthesis to tap about 4%. Dr Leggett reckons amorphous silicon tiles harvest as much as 8%. He has the equivalent of 1.4 kilowatts on his little roof in Richmond, Surrey. Even on a cloudy day, he argues, his roof provides the current for 350 cups of tea, 70 episodes of Coronation Street and 800 slices of toast.
"With it, in the four months I have been connected to the grid I have generated 670 kilowatt hours of electricity," he says. "I'm 68% ahead. I've exported 68% more than I have consumed in that period. It's very efficient at low light conditions. It gives the lie to the widely held view that we need sun to make it work and is only suitable for the South of France."
He began as a researcher into the geological history of the oceans and acted as a petroleum geology consultant, walking in each day through the portals of the Royal School of Mines at Imperial College.
The Cold War was hotting up, so he joined Scientists Against Nuclear Arms. He began writing for the Guardian's science pages. As a seismologist, he watched Cold Warriors claiming that since there was no way of detecting breaches of a test ban, there was no point in a test ban treaty. So he set up Vertic, the verification technology information centre, a London-based group which detected and confirmed a Chinese test explosion in the Lop Nor desert and announced it even before Washington could, or Beijing would.
From there he become scientific director of Greenpeace International and spent a decade fighting the international battle over fossil fuel use and global warming. Then he became an entrepreneur and now heads a business called SolarCentury, on the principle that money talks: if you can produce reliable power at less cost and with almost no pollution and show people that it works then it's better than shouting yourself hoarse about the environment.
"We worked out that we can sell these systems at about £10,000 per kilowatt - that's about 16.5 square metres - fully installed, with all the wiring, the electrics, the converters, connected to the grid, warranties in place. There are various ways of looking at that.
"Is that price going to come down in years ahead? Yes. The economies of scale in manufacturing are spectacular. The global market is showing signs of taking off. It grew at 40% in 1997, 32% in '98. In the first quarter of this year most companies' sales were up 40%. Warehouses were empty and the investors are getting interested. If you think about it, the prizes are very big."
The vision - not just his - is of electricity made on the spot, courtesy of the sun, every day, with the surplus exported to industry. Why build fossil fuel power stations that will stoke up global warming and clouds of acid rain as well?
Why spend millions on nuclear power stations which run for 30 years but have to be guarded for another 120 years before they can be dismantled? The electricity supply business, he says, is well on the way to becoming a trillion dollar business. There are no known constraints on the supply of raw materials for his preferred form of solar power supply: anything could happen and fast.
When John Battle, energy minister, and Michael Meacher, environment secretary, were in opposition, he set up an industry solar task force at their request. BP were in on it, along with Eastern Electricity, the Natwest bank and Guardian Royal Exchange insurance company. Norman Foster, the architect, was in on it. The conclusions, he says, was that global warming was a threat to the British economy and that solar photovoltaic systems could be the "single most important long term means" of achieving the deep cuts in greenhouse gas emissions. These were remarkable conclusions for big companies to reach. The Germans have a government solar power initiative for 100,000 solar-tiled homes by 2005, and the Japanese are installing 10,000 photovoltaic roofs a year. The Americans will have one million solar roofs by 2010.
In Britain, there is a 100-roof field trial and that is all. Dr Leggett is still waiting for Messrs Battle and Meacher to do something about the recommendations.
"I can't begin to understand why they aren't being acted on. It's in danger of becoming a national embarrassment," he says.
His new book, The Carbon Wars (Penguin) is an account of a bruising decade as an international campaigner, trying to persuade governments to take the atmosphere crisis seriously, in the teeth of a wrecking campaign by representatives of the fossil fuel industries. Most of the grim warnings uttered a decade ago still hold. Most of the hottest years ever recorded have occurred in the last 15 years, and 1998 was the hottest ever. It was also the most costly for climate related disasters. Governments have agreed on a convention on climate change, but it isn't obvious that politicians take the issue seriously.
Dr Leggett remains an optimist. He just decided to take the battle somewhere else. "I just figured why not have a crack at a huge prize, which is to create an investment vehicle, or even a series of investment vehicles?
"Rather than talking to these people in principle about what they might do with their money I could create something that becomes irresistible. Whether it works or not is obviously an interesting question for me - but I am completely convinced the solar revolution is coming, and it is going to create a vast new business revolution."
• The Carbon War: Despatches From The End Of The Oil Century, by Jeremy Leggett, will be published by Penguin at £20 on August 26.
