A solar system can be installed on a slate roof, weak or unusual tiles, however, even the most careful installer may occasionally break tiles and the home owner should anticipate this and have spares available. As per the NRCA Roofing and Waterproofing Manual (Fifth Edition), they recommend that “roof deck slopes intended for the application of steep-slope materials at 4:12 (18 degrees) or greater”. I have been looking for a company that can help with the selection and installation of a roof for a long time. Chose SunPower. Looked at various company reviews at https://solwiser.com/best-solar-companies/, they can give advice.