Guardian: The “clean tech” sector has bounced back from the credit crunch with new global figures showing a resurgence of interest from investors in alternative energy – labelled a “green Klondike” that could reach $600bn annually by 2020. New Energy Finance, a specialist consultant which has compiled the latest figures for the United Nations environment programme, says money raised and spent during 2008 should be ahead of 2007, a banner year when annual investment levels …