Wow!  Two disagreements without any indication why.  
In 1960 the average efficiency of PV cells was 14%.  Today, 2017, fifty-seven years later, the average efficiency of a PV cell is between 15 and 17%.  In Maryland, where the church in this article is located, the efficiency is going to see a maximum efficiency of 11-12% in the summer months, assuming someone gets to them monthly to clear off dust, bird droppings, etc.
Carter was not prescient because solar water heaters were around at least a century before Carter's presidency.