You sometimes see newspaper headlines to the effect that, say, a “50 megawatt solar power plant” is being constructed. But you shouldn’t count on getting anything remotely approaching 50 megawatts of power from such an installation. Energy expert Isaac Orr explains: Data from the U.S. Energy Information Administration (EIA) show that production from solar panels plummets in the winter. The graph below shows the percentage of electricity generated by solar panels in Minnesota compared to their potential output. This percentage is called a capacity factor in electricity-industry lingo. ... Isaac’s analysis applies specifically to Minnesota, but bear in mind that...