Returning to metropolitan France in 1878, Mouchot and his assistant Abel Pifre displayed Mouchot's engine at the Universal Exhibition in Paris, and won a Gold Medal in Class 54 for his works, most notably the production of ice using concentrated solar heat. However, the continuing economic benefits of the Cobden-Chevalier Treaty, combined with a more efficient internal transportation for coal delivery, meant that coal became increasingly cheaper in France, reducing the necessity for research into alternative energy. The French government assessed in a report that solar energy was uneconomical, deeming Mouchot's research no longer important and ending his funding.