*What DR JAM had given is absolutely correct, but i want to add more.
A one hundred watt light bulb, for example, is rated to consume one hundred watts of power when turned on. If such a light bulb were on for four hours it would consume a total of 400 watt-hours (Wh) of energy. Watts, therefore, measure instantaneous power while watt-hours measure the total amount of energy consumed over a period of time.
A megawatt (MW) is one million watts and a kilowatt (kW) is one thousand watts. Both terms are commonly used in the power business when describing generation or load consumption. For instance, a 100 MW rated wind farm is capable of producing 100 MW during peak winds, but will produce much less than its rated amount when winds are light. As a result of these varying wind speeds, over the course of a year a wind farm may only average 30 MW of power production. Similarly, a 1,000 MW coal plant may average 750 MW of production over the course of a year because the plant will shut down for maintenance from time-to-time and the plant operates at less than its rated capability when other power plants can produce power less expensively.
The ratio of a power plant's average production to its rated capability is known as capacity factor. In the previous example, the wind farm would have a 30 percent capacity factor (30 MW average production divided by 100 MW rated capability) and the coal plant would have a 75 percent capacity factor (750 MW average divided by 1,000 MW rated capability). Load factor generally, on the other hand, is calculated by dividing the average load by the peak load over a certain period of time. If the residential load at a utility averaged 5,000 MW over the course of a year and the peak load was 10,000 MW, then the residential customers would be said to have a load factor of 50 percent (5,000 MW average divided by 10,000 MW peak).
Knowing the peak and average demand of a power system is critical to proper planning. The power system must be designed to serve the peak load, in this example 10,000 MW. But the actual load will vary. The load might be 10,000 MW at noon, but only 4,000 MW at midnight, when fewer appliances are operating. The capacity or load factor gives utility planners a sense of this variation. A 40 percent load factor would indicate large variations occur in load, while a 90 percent load factor would indicate little variation. Residential homes tend to have low load factors because people are home and using appliances only during certain hours of the day, while certain industrial customer will have very high load factors because they operate 24 hours a day, 7 days a week.
· 1 decade ago