How does the energy efficiency of fuel cells compare with the energy of other methods of producing electricity?
On paper they are quite good - 90% theoretical efficiency is attainable for selected chemistries. In the real world, water-based fuel cells are remarkably awful for an impressively large number of reasons. Molten salt cells are much better. The trick to Enviro-whiner arguments is where to start keeping the books. An engineer starts with fuel source to get true net energy production, mining raw materials to rubber on the road. Enviro-whiners start with engine output, thereby slathering lipstick on pigs.
