This year, for the first time in the modern nuclear era, renewable energy has surpassed nuclear power as a percentage of U.S. energy generation. Nuclear power generation has been facing hurdles for a while: it’s expensive to expand, often politically unsavory, and not as competitive as the cheap natural gas that has flooded the market in recent years. But compared to its traditional rival, coal, nuclear power is significantly better for the environment. The worry, as costs and other pressures gradually diminished nuclear capacity, was that renewables wouldn’t be able to make up the difference. And instead, would lead to an increased reliance on fossil fuels.