I'm currently trying out the new Google Solar API. I've been following the guide in the docs which gives me the described JSON as a response.
However, once I visit the returned links followed by &key=API-KEY, it most often returns a completely black TIFF Image, even with the example location written in the documentation (e.g. in case of the maskUrl or dsmUrl images). Only the RGB image (rgbUrl) is returned as a proper image: