I always saw it as a very long-term solution. Once we have the lunar colonies, orbital space stations, asteroid mining, and the economic infrastructure to make interplanetary travel routine, we could begin building out SSP as a practically unlimited source of power. But, for the foreseeable future I have to agree with Musk. Considering how expensive launching stuff to orbit is right now almost any sort of terrestrial solar power coupled with an energy storage mechanism (e.g. pumped hydro, heat reservoirs for solar thermal) would be more cost-effective.