At long last, the tipping point is nigh: For the first time in modern history, clean-energy technologies are becoming cost-competitive with their “dirtier” counterparts. While oil and natural gas prices remain stubbornly high and frustratingly volatile across the globe, and as nuclear and coal-based energy remain dogged by environmental and safety concerns, clean-energy prices continue their near-relentless downward march. Consider wind power. In certain regions, it is now one of the least expensive and most easily deployed sources of new generating capacity. Or ethanol, which has gained favor for vehicle use in both in the U.S. and abroad. Or biodiesel, made from a wide range of animal and vegetable oils, whose price is within striking distance of petroleum-based diesel. Even solar, still relatively expensive without subsidies, competes favorably in some places and is often the cheapest choice for power in remote regions. Suddenly, so-called “alternative” energy technologies are looking pretty mainstream. The growth of clean-energy markets reflects its growing acceptance. Global wind and solar markets reached $11.8 billion and $11.2 billion in 2005 — up 47% and 55%, respectively, from a year earlier. The market for biofuels hit $15.7 billion globally in 2005, up more than 15% […]