100 square miles is small in the American southwest. And a solar farm would disrupt the ecosystem much less than many other land uses. Adding shade and cover will benefit many species.
Burning 10GW of fossil fuels for 20 years while waiting for the nuclear plants to finish building will do far more damage to the environment than 100 square miles of shade in the desert.
Environmentalists are just against progress. A few desert species going extinct is not a big deal. It's an arid wasteland. When we eventually terraform it (with desalinated water from solar / fusion) those species are going to die out anyway.
