According to this Ars article, project sunroof was a 20% project: http://arstechnica.com/business/2015/08/here-there-be-photons-googles-project-sunroof-maps-sol

According to this Ars article, project sunroof was a 20% project: http://arstechnica.com/business/2015/08/here-there-be-photons-googles-project-sunroof-maps-solar-panel-savings/ http://arstechnica.com/business/2015/08/here-there-be-photon... (see next-to-last paragraph)