From SolarReviews.com:
There are several different types of solar companies, and there are significant differences between them.
Large corporate solar companies
These are companies like Tesla, Sunrun and Vivint Solar with corporate ownership and wide geographical coverage. When residential solar took off back in 2012, they were the first to offer zero-down solar options and thus gaining massive market share. However, these companies grew too quickly and were unable to maintain the quality of their customer service; this is reflected in their poor review scores on SolarReviews and other sites. Furthermore, these large companies face stiff competition from local solar companies who now offer zero-down financing via specialist solar loan companies. Indeed, in a bid to stay competitive, in July 2020 Sunrun and Vivint, the largest companies by market share, announced they were merging.
Local and family-owned solar installation companies
These companies are typically one-stop shops that both sell and install solar systems. They are more likely to employ their own installation team rather than outsourcing the task. This is a good thing: our reviews indicate that customers are more satisfied with jobs performed by in-house crews.
Solar sales companies
These are companies that sell solar to homeowners over a large geographical area, but rely on outsourced installation labour to supply all the equipment, manage the permitting, and perform the installation. For example, they may sell you a solar system for $15,000, but then pay an EPC contractor $12,000 to supply and install the entire job. These companies also tend to have super-aggressive sales tactics, and we generally see low customer satisfaction for consumers who sign with them.