Sterno is basically jellied alcohol. You can read about it on Wikipedia. Like liquid alcohol, it is a low energy per weight fuel; probably less than liquid alcohol because of the weight of the gel and some added water.

If you are looking for efficiency, Sterno isn't the ideal fuel. Simple, yes, efficient, no. The only time I recall seeing Sterno is under a chafing dish at a buffet.

If you want an alcohol stove, there are many good designs out there that require only modest skills to make, or you can buy one from a number of cottage stove makers.

Remember-making soup is not cooking-it's heating water.