Business Green: Thin-film solar cell manufacturer First Solar yesterday announced it has broken the $1 (70p) per watt cost barrier that is widely accepted as the point at which solar panels become cost competitive with fossil fuels. The company said that during the fourth quarter of last year, the manufacturing cost for its solar modules stood at 98 cents per watt, taking it below the $1 per watt mark for the first time. Mike Ahearn, chief executive at the company, hailed the achievement as a …