When we use electricity, the electricity is pushed through an electric device (anything that uses electricity to run) by the electric potential called voltage. The voltage is like pressure in a water system. The amount of electricity pushed through the device is the current, which is just like the flow of water in a pipeline. The power of electricity used is the voltage multiplied by the current. This simple relationship is defined by Amperes of current multiplied by Volts of pressure equals Watts of power. Any electrical device, generator or consumer uses this relationship of voltage and amperage to determine the power generated or used. Fundamentally, we make electricity by pushing (voltage) the electricity through the wires at some volume rate (Amperage).
Our electric using devices (“end uses” of electricity), were each designed to perform some function, anything from making a certain amount of light to making some sort of work, think of an electric motor, to making heat. Remember that most electricity is made from heat, so we can turn the electricity back into heat. By looking at the nameplate on any electric device in the US you can tell the voltage and amperage the device needs to do its job. Some nameplates also tell the wattage or power required by the device, but remember power in watts = volts * amps. So in order for this device to do what it is supposed to do, it has to have the volts and the amps to do the job. Because it has to have this power, it demands the power. This is why we call the power needed by the device the demand of the device. When we use a number of devices in our home, business, or industrial plant, this demand adds up by the individual demand of each device that is operating at the same time. Collectively, this is called the home’s demand, the business’ demand, or the industrial plant’s demand. In all of the cases, the demand is the same thing as the power needed, and this power needed is provided by the utility. Another word for power from the utility’s perspective is capacity. The utility has to have the capacity to provide the power demanded by the customers.