Energy Densities

Energy Density

This graph shows system energy densities. By “system”, we are taking into account typical efficiencies of the systems that these chemicals are used in. Note that the closer a system reaction is to the upper right hand corner of the graph, the better the overall energy density. A direct methanol fuel cell (DMFC) can exhibit higher efficiency and comparable energy density, but problems like cross over tend to kill its ability to be a legitimate reactant. An ICE typically has poor efficiency (around 35%), and is mathematically limited to around 48%. This cannot compare with fuel cells that operate typically in the 60% to 90% range. Please note that a hydrogen fuel cell has excellent gravimetric energy density, but volumetrically is poor; it must be stored in high pressure tanks that are unsuitable in a vehicle.