Real power

Most appliance and consumer equipment manufacturers rate their equipment in units of real power. In the electric industry, the standard unit used to quantify the amount of electricity used by a device, or its ability to do work, is the watt or wattage of the device. The symbol used to represent wattage is W.

Let’s look at an example. If you have a hair dryer that operates at 1200 watts, that hair dryer is consuming 1200 watts of power from the electrical system every instant it operates, and in turn it is capable of providing a certain amount of flowing air and heat. So how does a 900 watt hair dryer compare with this 1200 watt dryer? You would expect the 1200 watt dryer to dry your hair faster because it produces more heat and flowing air than the 900 watt dryer, assuming the two devices operate at the same efficiency. This is because the dryer that consumes more power does more work. In terms of real power and appliance ratings, the higher the rating of the appliance, the more work it can do. Devices such as incandescent light bulbs and heaters consume only real power. And since they consume no reactive power, their apparent power is equal to their real power. Other devices such as motors and fluorescent lights consume both real power and reactive power.

While appliance manufacturers rate their equipment using the watt, power suppliers typically find watts to be too small of a quantity and measure real power using kilowatts (kW) or megawatts (MW). A kilowatt is 1,000 watts and a megawatt is 1,000,000 watts. 

Most electric power suppliers use the kilowatt to quantify how much power, or demand, commercial and industrial customers consume at any given time. Here you can see customer usage or demand over a 24-hour period, with midnight represented as Hours 0 and 24. As you can see, from midnight until about 6 a.m., this customer’s demand is steady at about 10 kilowatts. At 8 a.m., however, the demand from this customer increases dramatically. This is typically due to workers beginning their day by turning on various equipment at the facility. At about 4 p.m., this customer is at its peak demand, which today is around 37 kilowatts. The higher the demand, the more power the customer is using at that particular time of day. Later in the day, as workers shut down equipment and return home, demand continues to drop until the customer’s demand again reaches the baseload level of 10 kilowatts. Demand, then, is the amount of power a customer consumes at a given point in time.