Silicon Valley-based SolarCity announced today that it will extend its $0-down solar power purchase agreement (PPA) to the majority of its California residential service area until the end of July.

The program, called SolarLease, is the first installer-led residential solar leasing option available, according to the company.

SolarCity debuted its promotional program last week as a response to a challenge by San Jose Mayor Chuck Reed at the launch of the California Cleantech Open on October 5th, for a solar installer to offer a no-money-down leasing option to residents.

According to the company, SolarCity was the first to respond to the challenge and is extending the 100-day promotional offer to customers in most of its California service areas, but has not announced any plans to extend to its other service areas in Oregon or Arizona.

PPAs are traditionally offered to larger, commercial installations (for instance, see Ormat signs 20-year geothermal PPA with Nevada Power Company, or Eight cleantech developments to watch for in 2008) to remove the barriers to adoption of clean energy sources.

SolarCity said it hopes to allow families to begin generating a positive return on their solar investment, at an affordable price point. As an example, it said a homeowner with a $150 monthly electricity bill could switch to a 3.2 kilowatt solar system for $0 down, an initial monthly lease payment of $90 per month, with a greater than $100 monthly reduction in utility bill—making solar less expensive than tradition energy.

SolarCity’s residential PPA financing mimics programs made available to commercial customers, and allows residential customers the option to purchase the system, upgrade, or have it removed at the end of a 15-year lease.