If I understand the article correctly, there is no boiling water, it uses hot air only. It says the concentrated solar generates air up to nearly 1000 degrees, and that's used to heat up compressed air to run through a turbine, with the eziting air at around 250 degrees. Burning fuel would replace the initial source of hot air. Burning fossil fuels to get hot air and then dumping 250 degree air to the environment doesn't seem very efficient, but the article doesn't mention anything about the efficiency of the process with either source.

Does say the hot air at the end can be used for industrial processes, so it might not be completely lost