“It’s not going to handle a day, a week, a month, a season,” said Moniz

I believe that way solar thermal based approach is going to be future; energy stored in form of intrinsic heat of a liquified salt solutions (by the concentrated solar beam), or may be for that matter simply inside heated stones (by solar CSP), and then passing water to convert in steam and run turbines!! But ya that will be for grid level solution, not the mobile electronics' power source.