That captures the most solar energy over the course of the day, which benefits the homeowner, but does so at hours that are not so helpful for the utility and the grid as a whole.

Mount them to catch the sunlight from the west in the afternoon, and the panels’ production over all would fall, but it would come at hours when the electricity was more valuable.

via Why More Solar Panels Should Be Facing West, Not South – NYTimes.com.