Business Green: The US solar industry ticked off a major milestone last week with the unveiling of the country’s first solar thermal tower in southern California. The 5MW Sierra SunTower solar plant features 24,000 mirrors that have been positioned to concentrate the sun’s rays on two 160-foot towers containing water that is then turned into steam to drive turbines. The resulting energy is expected to provide power for more than 4,000 homes in California’s Antelope Valley. The plant has been …