kWh and kVA Explained
Kilowatt-hour (kWh) is the measure of energy consumption (power over time). As an example, a 60 watt light bulb burns power at the rate of 60 watts (or 0.060kW). In one hour, the bulb will consume 60 watts times 1 hour, or 60 watt hours). In 12 hours, that same bulb will have consumed 60 watts times 12 hours, or 720 watt hours (0.72kWh). kWh is a unit of energy.
When we talk in terms of power; there are two kinds: Real Power and Apparent Power.
Real Power: Kilowatt (kW) is also a unit of electrical power (equal to 1,000 watts), referred to as Real Power. This measure of power is also called demand. For a 60 watt bulb, the demand would be 60 watts.
Apparent Power: Kilovolt-Ampere (kVA) is a unit of electrical power, often referred to as Apparent Power. This is what the utility must supply to its customers on the primary side of the facility transformer and is the basis for sizing power plants.
Different customers may use the same amount of real power (kW), but different levels of apparent power (kVA) depending on the kind of equipment in they use. Equipment with lots of magnetic fields (like electric motors) will require more apparent power to feed the same real power demand. If you know the kilowatt demand (real power), then you can calculate the electrical energy consumed over time (kW x time = energy).
Lets use the analogy of a car: kVA or kW is like your spedometer, and kWh is like your Odometer. The more power you use at any given time, it will be like driving the car faster, making the odometer increase at a faster rate, or in this case, kWh will increase at a faster rate. Your odometer is how far you have driven, even if you turn everything off and shut the car down, you have still driven the kilometers indicated. Sometimes we drive fast, sometimes slow, and the odometer reading changes accoringly.
NOTE: kWh values shown live are the accumulated kWh since the meter was installed; various meters on campus have been installed at different times. To compare energy usage between different buildings, you need to compare the difference between the end of a given period and the kWh at the end of the period. So if you wish to compare the daily usage, record all the kWh values at the start of the day, and at the end of the day and subtract the two for comparison.