That's a neat project. A key difference is the Google dataset resolves down to the address level (at least in the US). So it is able to account for tree cover over individual buildings, which can be determinative to the economics of a solar install.

DC uses Palmetto mapdwell, which is the solar potential analytics platform + api that pepco, comed, exelon, bge, peco, etc. all use.

https://mapdwell.com/en/solar/dc

This is the data that I took to my building's HOA board when proposing we retrofit our rooftop with solar.

The demo in the article is way beyond this. They have elevation models of each house and optimize number and placement of panels.

I believe OpenSolar.com is another alternative