Elon Musk is expected to unveil a new solar roofing product for his energy company, SolarCity, this week. Based on what Musk has already said about the product, his solar roofing would put the photovoltaic cells used to generate electricity from the sun in the shingles themselves, instead of in a system of solar panels on a roof. When the billionaire tech titan teased the product in August, he vowed it would be all but unrivaled ― “a different ballgame.” On that claim, Robert Allen is calling Musk out. Allen is the president of Luma Resources, a solar roofing startup based in southern Michigan.