Power grid operators in the U.S. are looking forward to Monday’s solar eclipse as an opportunity to test the impact of renewables on the power networks. The eclipse offers a completely predictable stage for experiments. It’s not often that utilities get such precise and advance notice about more than 12,000 megawatts of solar power supplies set to suddenly drop off their systems. The test will help utilities prepare for the day when renewable energy becomes the world’s dominant source of power.