How Tesla failed to maintain a huge lead in residential solar, and why Elon Musk is unlikely to win it back

· SolarCity dominated the rooftop solar industry in the years before it was acquired by Tesla in 2016.
· Now the firm, part of Tesla's energy business, has just about 5% of the market, according to the research firm Wood Mackenzie. 
· What happened? SolarCity was a huge solar installer, but it was struggling financially...