One further difference between the two has to do with their emergent properties. From the demand-side perspective, the emergent property based on the system output is of particular importance. RES distinguishes between several types of outputs, while the load curve handles the variations of one output over time. According to Marcuse et al. The terminology points out the stepwise conversion of energy from source to consumer.
Primary energy is an available energy source.
Secondary energy is energy that is converted in a central conversion unit, e.g. a refinery, and that requires further conversion to final energy before delivery to the end-use sector. The final energy is then converted in end-use appliances to useful energy. The useful energy is the energy part of the utility that the customer demands e.g. illumination, kinetic energy, and heat. The model is a flow chart in which all energy flows in the energy system can be traced. Thus, the model obeys the first law of thermodynamics.