Kilowatt and Kilowatt Hour Explained

 In Electric Utilities, EV Charging, EV Industry

***Updated November 30th thanks to great feedback from our readers.

As someone new to the electric vehicle (EV) industry, I know working and understanding measurements of energy can be very confusing.  To that end, two of the most confusing and misunderstood terms are the kilowatt and kilowatt-hour.  These terms are put into action all around us on a daily basis. Your electric bill is centered on these terms and how they are used to figure energy expense.  For those of us who wish to, or currently, own and operate an EV, understanding these terms and how they interact is crucial to truly understand the benefits of using electric energy for transportation in an economical way.

What is a kilowatt?

A kilowatt is a unit of power.

Now, we just need to know what power is. Simply put, power is the rate at which energy is generated or used and the kW is a unit of that power. If we break a kilowatt down even further to the base unit of a watt, we start to understand it better. A kilowatt is equal to 1,000 watts. A watt is also a unit of power and can also be expressed as 1 joule per second. All these terms start to get confusing, right? What if we think about it like this:

A joule per second, a watt, and a kilowatt are all measures of power. Just like a millimeter, centimeter, and meter are all a measure of displacement (length/distance). They are all just different ways to measure the same thing.

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A watt is a small number in comparison to most electronic applications, hence using kilowatt as the measure (it’s like saying, “I just spent $25 on that shirt” over saying, “I spent 2,500 pennies on that shirt”).  The output of engines, tools, machines, and even heaters are all measured in kilowatts. So for example, the more things you run in your home, the more power your home will draw from the grid and your energy usage(kW/h) will go up. The average American household typically uses roughly 10,000-kilowatt hours per year.

What is a kilowatt hour?

A kilowatt-hour (kWh) is a unit of energy.

Energy is a way of measuring how much fuel is contained within something, or used by something over a specific period of time. A kilowatt-hour takes the same things we know about a kilowatt and applies it over a constant load over a specific period of time.  As you may have guessed, that time period is one hour.  A kilowatt-hour is a unit of energy equivalent to one kilowatt of power that is sustained over a one hour period.

energy = power x time or kWh = kW x 1-hour

Sound confusing right? Using what we have learned to this point, we can use a heater as an example to really understand how a kilowatt hour is used. If we take a heater that is rated at 1,000 watts, or 1 kilowatt, and we run that heater for an hour, then we have used one kilowatt-hour of energy.  If we were to take a power tool that is rated at 2,000 watts or 2 kilowatts, and ran that power tool for one hour, then we have just used 2-kilowatt hours of energy.  

Common confusion of the terms

It is no secret that energy measurement and consumption can all get pretty confusing.  The most common confusion of these terms is simply what each one of them represents and how it is applied to everyday life.  The kilowatt is simply 1,000 watts.  A watt measures the rate at which electrical power is used or generated.  In comparison, a kilowatt-hour is a unit of energy equivalent to one kilowatt of power expended for one hour of time. The greatest mistake tends to be that most people will use the kilowatt-hour together with a kilowatt.  It is absolutely crucial to understand that a kilowatt hour is a separate unit of measurement that attached a time period to electrical energy usage.  This is how electric bills are figured.  A kilowatt-hour is dependent on a constant energy output being used over a one hour period.  It is a separate measurement.  

How many kilowatt hours to charge my electric vehicle?

We are finally down to the million dollar question here, huh? Understanding all of these terms is all well and good, but how does it affect me? Why is figuring the number of kilowatt hours I would be using to charge my EV be important? Well, the concept of electric vehicles is focused on economically friendly transportation that is both efficient, stylish, and conducive to a stable budget.  For those who are looking to purchase an electric vehicle, it is important to understand how it will impact a budget compared to an internal combustion engine (ICE) vehicle.

The simple truth is that it will be much cheaper to power and run your vehicle on electric power as opposed to a fossil-fueled powered vehicle. ICE vehicles typically measure efficiency in miles per gallon.  In Canda, EVs are typically measured in kilowatt-hours per 100 kilometers.  Calculating how much you can expect to spend is not difficult.  If we figure how much electricity cost in kilowatt hours as well as the efficiency of the vehicle, meaning how much electricity it will take to go 100 kilometers, we can figure it pretty easily.

If electricity costs $0.11 per kilowatt hour, and the vehicle consumes roughly 21-kilowatt hours to travel 100 kilometers, we can figure that the cost per mile is around $0.04.  To figure the cost of “filling up” your electric vehicle, simply take the battery size, which is measured in kilowatt hours, and multiply that number by the price of electricity per kilowatt-hour.  A 24 kilowatt-hour battery will cost between $2.10 and $2.75 to fully charge.  Economically speaking, it is a wise investment.  This cost to fill up a charge for an EV is equivalent to a central air conditioner running for 5 hours.  

Did this article help? Let me know in the comment section below. 

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  • LP

    Interesting, but after all the discussion of kW & kWh, doesn’t answer the question of calculating demand capacity or demand charge on filling vehicles. PS – I use the analogy of having a bucket of water be the energy used. You can fill with a garden hose or fire hose. The hose diameter is the demand capacity and you need to pay for the larger demand.

    • Steve Love

      I would like to see electric cars come with a triplog feature that shows a continuous readout of the cost of each mile (you would plug in your local rate and it would calculate the cost per mile as you go). Seems like this would be easy to do and would really impress drivers and possibly spur even more EV ownership. The public is slowly learning about the lower costs of EV ownership and most have yet to experience the superior performance and fun driving experience they offer.