SAN JOSE, Calif.  And California begat cars, and the cars begat asphalt parking lots. And the lots spawned electricity, transforming the hills and the deserts.

Ersatz roofs made of solar panels have sprouted above dozens of school parking lots in the state, altering vistas and promoting a philosophy of green thinking among the young. Yet the primary driver of the solar roofs is economic.

By forming partnerships with banks and other backers, school districts get guarantees of reliably cheap electricity for their buildings for as long as 20 years. The institutions, which finance the systems and sell the electricity back to the schools, also receive tax incentives from the federal and state governments.

So far, solar carports have been installed at some 75 elementary, high school and community college campuses in California, the majority of them in the San Francisco area. Some are designed as a broad fan of panels canting slightly upward and supported by a single pole; more often they are an ode to rectilinearity, parallel to the asphalt and supported by a line of poles between the rows of parking spaces.