With the current color scheme, the highest value data point is also the least visible. Yellow intuitively signifies solar potential, but the light grey background makes yellow very difficult to see.
Here's a mockup of the data with a dark blue background, which makes the data much easier to see. Built with Google's own map style maker, I used the following parameters: roads = 100%, landmarks = 0%, labels = 0%, color = "Aubergine"
If you're aware of any similar tools designed to estimate solar energy potential, please link to them in the comments below. I'll try to add them to AlternativeTo.com, my favorite site for finding alternatives to specific apps and services.