All fats have roughly the same caloric content, in the neighborhood of 100-120 calories per tablespoon, so if it really were a half cup of pure fat, it would be about the same calories as half a cup of oil (800 - 960).
BUT... It wasn't pure fat. Some of what you skimmed off was water from the vegetables, etc, and gelatine from the meat. It's still definitely useful to skim it (and you can do that even if you cook on the stove; just chill it in the fridge, skim, and reheat), but if you can't, you're not eating an extra 960 calories.