On March 20, the solar eclipse put the German power grid to the test. In recent years, renewables-friendly policies have led Germany to amass the largest base of installed solar generation capacity of any country in the world. Now, with the sun set to vanish, questions were being raised about whether the lights would stay on.

TenneT TSO, a subsidiary of Netherlands-based TenneT and one of Germany's four transmission system operators, was ready. In October 2014, it had launched a new trading desk