Keep reading the thread. You'll see plenty of people who disagree (and even the PDF is inconsistent), and even a couple who tested it out and found it does indeed go well below 77 degrees. It simply doesn't allow full power operation below 77 degrees, but falls off to a lower power level. This means that in very hot, sunny conditions it might not go below 77, but it can at other times. In the PDF, see the very last page for a chart of AC power versus temperature. It never drops to zero.

Remember that the manual is translated from Japanese and sometimes things are lost in translation.