SolarCity installed 29% of the residential solar PV capacity in the United States in the first quarter of 2014, according to a report by GTM Research. This is an increase from its 27% share over the full year 2013.

Vivint came in a distant second with a 9% market share, followed by Sungevity, Verengo and Solar Universe. GTM's U.S. PV Leaderboard finds that these top five installers made up 45% of the nation's residential market, up from around 42% in 2013.

Third-party solar providers have taken the largest share of the U.S. residential market in key states. And while other third-party companies work through networks of installers, SolarCity remains the largest in this space in any metric.

Report lead author Nicole Litvak also says that consolidation in the space is happening due to the organic growth of the larger companies, and credits effective sales strategies and a large referral potential from the base of existing customers.

Litvak also says that much of the reason for the success of third-party solar companies is due to factors other than the third-party financing model. “One of the reasons that we are seeing so much third-party ownership right now is because of the stronger sales capabilities of the installers and the companies who are offering third-party ownership.”

“SolarCity and Vivint have just been the best at reaching customers. And if they are the first ones to approach a customer and they can pitch them a lease or a power purchase agreement, then they won't bring up the loan option. I think as consumer awareness increases, and people become more aware of the options, then we could see more loans and direct purchases, or a change in the installer landscape and the market leaders.”

GTM Research expects the U.S. residential PV market to grow to over 1 GW in 2014, driven by expanding options for financing. The company expects the share of third-party financed solar to peak in 2014, with loans and cash purchases to become more prominent in coming years.