The smaller the temperature difference, the worse the efficiency. The linked article said it got up to 85C, if you assume the cold end gets down to 25C, you cou

The smaller the temperature difference, the worse the efficiency. The linked article said it got up to 85C, if you assume the cold end gets down to 25C, you could only recover 16.753% of the thermal power as useful work, theoretical maximum Carnot cycle.