1. A method to calculate energy demand in an energy generation, transmission and distribution network, comprising one or more power plants based on different energy source types including renewable energy, a communications system and one or more local consumption metering units, comprising: providing a customer demand profile for one or more customers, registering a customer-specified proportion of power demand to be supplied from a given energy source type, and calculating a total predicted energy demand dependent in part on the accumulated demand for the given energy source type.