Solar car speculation drives 2015’s hottest ETF

Technicians install solar panels on a house in Mission Viejo, Calif.
Mario Anzuoni | Reuters
Technicians install solar panels on a house in Mission Viejo, Calif.

With oil prices more than 40 percent lower than a year ago, you would think Americans would be buying giant cars, turning up the thermostat and ignoring solar power stocks and related exchange-traded funds.

Then why is TAN, the Guggenheim Solar ETF, up more than 14 percent over the past year—essentially matching the performance of the S&P 500—and up more than 40 percent year to date?