[vectorwhat]

From your document it seems that the researchers ignored the most energy intensive part of the process!

From your document:

"Purifying and crystallizing the silicon are the most energy-consumptive parts of the solar-cell manufacturing process."

"To calculate payback, Dutch researcher Erik Alsema reviewed previous energy analyses and did not “charge” for the energy that originally went into crystalizing microelectronics scrap."

The way I understand it, the calculations don't charge the most expensive part of the process by arguing that, being scrap of the semi-conductor business, its already been paid.