Whats the Difference between kW and kWh? And What Does Kilowatt & Kilowatt Hour Actually Mean?
No matter if you’re an engineer, elementary school teacher or an energy consumer like the rest of us, it’s important to understand the difference between Kilowatt (kW) and Kilowatt Hour (kWh) to help you fully grasp energy concepts, calculations and potential savings metrics. Not to mention, if you take the time and learn now, you might save yourself a few embarrassing moments in the future, when your head starts spinning after your solar installer starts speaking what seems to be Mandarin about your energy demand and consumption.
To begin…
kW is a measure of power, while kWh is a measure of energy
If you’re like most people, you probably don’t know what the difference is between power and energy, or even knew there was a difference to begin with, so let’s start there and work our way forward from the source.
What is Energy?
Well, in physics, energy is a property of objects, transferable via fundamental interactions, which can be converted into different forms, but cannot be created nor destroyed. In a simplified socioeconomic
application, that we could more easily understand, we could say that Energy is the amount of fuel
contained within something, and used over a long period of time. kWh is a specific unit of measurement for energy.
The Kilowatt Hour is a unit of energy, just like a Joule is a unit of energy, or a Calorie. One Kilowatt Hour kWh is equivalent to 3.6 million Joules. Other units of energy could be the British Thermal Unit (BTU), erg, or thermodynamic kcal.
For example, let’s say that you’re eating a pack of pretzel m&m’s and it contains 1 70 calories. What that really means is that your m&m’s, contain 1 70 units of caloric energy, Calories. Which is equivalent to nearly 0.2 kWh.
Energy can change in shape and form.
Since energy is transferable through fundamental interactions, when you ingest m&m’s, those Calories or units of Energy are transferred and utilized by your body, to perform different fundamental actions and create other reactions, changing shape and form. Another reaction, in which the m&m’s could change shape or form could happen if you were to burn it, transfer that energy into heat energy, and with the proper equipment produce electric energy, to run lights, your coffee pot, fans etc.
But would we really burn the m&m’s to attain heat energy, in order to transfer into electrical energy?
Probably not! The best option is going to open that pack of pretzel m&m’s and eat them one by one. But, this shows how energy can be converted into different forms through different reactions.
What is Power?
The Kilowatt is a measurement of power, meaning one thousand watts, while the Megawatt (MW) means one million watts. The watt is measured in terms of power, or at the rate at which energy is generated or used.
For our sake, power is a measure of how fast something is generating or using energy. Power is not
creating energy, it is only the measurement of its transferable conversion from one form to another.
The Watt is a unit of power. The Watt is the same thing as Joules per second J/s, except that the Watt is a measure of power and J/s is expressed as units of energy and time together. Why do we have the same measurement to represent one thing? Someone along the road, decided that power needed it’s own specific unit of measurement, that we could slap on our light bulbs, and refer to how big our amp size is. Well at least, that’s my guess!
Joules per seconds can be thought of similarly to miles per hour. Joules per second, uses as its
indicating rate, at which energy is being generated, transferred or used. Miles per hour uses speed as its indicating rate, at which distance is being traveled.
Therefore, Joules per second J/s is a unit measurement for power, Watt is a unit measurement for power, Kilowatt is a unit measurement for power and Megawatt is a unit measurement for power.
What types of equipment generate power?
Renewable energy forms such as Wind Turbines, Solar Panels, Underwater turbines, and Solar Attic Fans take a form of energy, wind, the sun, water currents etc., to produce electricity, and heat! Boilers and power generators are fueled by energy from coal, burned fossil fuels that create heat and transfer that heat into electricity.
The rate at which these types of renewable energy sources can produce energy, is how much power they may have. For instance, a solar panel can typically produce around 200 watts of power. If you have a solar array with five panels, your production capability at its optimum level would be 1 000 watts, or one Kilowatt kW of power.
You may ask, how long does it take to generate one kW? Wrong! That’s similar to asking, "How long does it take to travel 1 0 miles per hour?" It makes no sense.
1 kW is the at which the Solar panel array can generate energy, not the of energy that it can
generate in a certain period of time.
Energy Demand
Many times you will hear people talking about the energy demand or peak demand of their home, office, or warehouse. Energy demand is simply the amount of energy used over a period of time.
For example, one 1 00-watt light bulb burning for 1 0 hours consumes 1 ,000 watt-hours or 1 kWh. The entire time it is on, it requires or "demands" 1 00 watts or 0.1 kW from the utility.
Peak demand is the time of day, in which you’re using the most energy. If you’re at your home and you turn on a light switch in the bathroom, then you have Instantaneous demand. Instantaneous demand, Instantaneous power, and Instantaneous load are referred then to the utilization of energy at any one moment in time. The light switch you turned on may be 1 00 watts, which means that when that light switch is off, you have no instantaneous demand. However when you turn that 1 00 watt light back on, you have an instantaneous load, or demand of 1 00 watts of power, at that particular time. When it’s turned off you have an instantaneous demand of 0 watts of power.
Average Power
The average power of something, indicates how much power that particular energy source can produce over a given amount of time on average. A given amount of time could mean a day, week or even a year. Earlier, we noted that our solar panel array had the capability to produce 1 kW of power (1 000 watts). If that solar panel array was then producing energy at it’s optimum capabilities of 1 kW during 1 2 hours of the day, and 0 kW for the other 1 2 hours consistently for one week, then we could say that the average power of our solar panel array over a one-week time period, is 500 watts.
Conclusion
It can be daunting at times to calculate energy savings, average consumption, or demand. But by learning the basics, at least you can understand the fundamentals of power and energy, and the unit
measurements of Kilowatt and Kilowatt Hour, so that you can understand and interpret their true
meanings. It also makes for a good conversation piece.
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