Abstract: A method of controlling an electrical power supply to a load, wherein said load has an associated power threshold, is provided. The method comprises using a first electrical power source to generate a first amount of power for supply to the load, wherein said first electrical power source comprises a renewable source, and determining whether to supply a second amount of power to the load from a second, different electrical power source. If it is determined that the second electrical power source should be used to supply a second amount of power to the load, controlling an output of the second electrical power source so that a combined amount of power supplied to the load from the first and second electrical power sources meets the power threshold associated with the load.