A year ago, Los Angeles set out to become the “Solar Capital of the World,” announcing that 100,000 roofs in the city would be covered with solar panels by the end of the decade. The city said it would reimburse people for half the price of a new solar system, which can run from $10,000 to $20,000, parts and labor included, before the rebate. Only 40 systems have been installed so far. Gulp. Why the slow pace? For one, the city’s lone panel manufacturer hasn’t been able to keep up with demand. Also, not that many L.A. contractors know how to install the things.