The article's here if anyone's interested - http://www.guardian.co.uk/money/2008/apr/19/householdbills.consumeraffairs2?

The family of four have produced 92% of their electricity usage from the roof of a century-old terraced house in south-east London. The, "...system works by producing power - up to 3 kilowatts - during the day and exporting much of it to the grid because we are out at work and school most days. It's fun to watch our old-fashioned meter spinning backwards when the sun is shining."