Defining kW & kWh
A Lightbulb Joke
A man walks into a hardware store and speaks to the cashier. “Do you have any two-watt bulbs?”
Cashier: “For what?”
Man: “That’ll do, I’ll take two.”
Cashier: “Two what?”
Man: “I thought you didn’t have any.”
Cashier: “Any What?”
Man: “Yes, please!”
Cashier: “Any What?”
Man: “Yes, please!”
“Kilo” is just a prefix that means 1000, so $1000W$ are equal to $1kW$, and $1000Wh$ are equal to $1kWh$. There are other prefixes as well, Mega ($M$) = 1,000,000, centi ($c$) = 0.01, these are part of the metric system. To see a whole list of prefixes just Google “Metric Prefixes”.
$ 1000W=1kW $
$ 1000Wh=1kWh $
When distinguishing between $kW$ and $kWh$, or Power and Energy, it’s important to understand how they are measured.
$kW$, power, is the rate at which electricity is delivered.
A $kWh$ is not a standard unit of energy and is only seen in terms of electricity. It is the amount of one $kW$ of power flowing for one hour. In many other applications energy is measured in Joules ($J$). Therefore,
$1kWh=3.6 \times 10{x}^{6}=3.6 \: Million \: Joules$
In summary, $kW$ is power and measured at a specific time. $kWh$ is energy and is the amount of power used during one hour, or during many hours.
Example 1
A $100W$ lightbulb used for 2 hours has used $0.200kWh$.
$ 100W=0.100kW $
$ 0.100kW\times 2hr=0.200kWh=200Wh $
Application in Utility Data
Utility companies look at both your power and energy consumption. Power is often referred to as “demand” because it is the amount of power at any given time you are demanding from the utility company. The electrical grid can only provide so much power at any given time which is why you may have experienced a power outage during a very hot day in the summer time. HVAC is often the highest consumer of demand and energy in a building. During 1:00pm on a hot and humid day while everyone is blasting their AC units, the utility companies charge you the most because they have high demand for electricity.
Let’s continue to dig…
Whether you receive your electricity data from the utility company or you are measuring it yourself, there are two important factors to consider: the unit you are measuring in and the duration you are measuring for.
Electricity meters can measure in either kW or kWh. Some typical time durations are hourly, half hour, or 15 minute. You can also measure in 10 or 5 minute intervals, but I always found that 15 minute was small enough, smaller than 15 minutes tends to be too much data to handle for little gain. This is same when receiving utility data from the electricity company. Depending on the meter on the house, there are different formats you can receive the data in and it is important to note.
Consumption vs Demand
So you have your data in hand by either measuring it yourself or from your utility company, and now you want to analyze it. The two main values that are used in anything electrical such as analyzing electrical usage, determining utility bill amount, sizing solar panels, saving energy, creating a building profile…the list goes on, are electrical consumption and demand.
Consumption ($kWh$) = is the total amount of energy consumed
Demand ($kW$) = is the max power
Data received in kWh
Measured by hour
Consumption ($kWh$) is equal to sum of all your data.
Demand ($kW$) is equal to your highest measurement of that day, week, month, or year, depending on the during of time you are analyzing.
So if your max kWh measurement was at 1:00pm, 34 kWh, max demand is equal to 34kW.
$\frac{34kWh}{1hr}=34kW $
Measured in 15 minute intervals
Consumption ($kWh$) is equal to sum of all your data.
Demand ($kW$) is equal to your highest measurement of that day multiplied by 4. This 4 is because there are (4) 15-minute intervals in one hour.
$ (4)15min=1hr $
$\frac{34kWh}{15min}\times \frac{(4)15min}{1hr}=136kW$
$\frac{34kWh}{\cancel{15min}}\times \frac{(4)\cancel{15min}}{1hr}=136kW$
$\frac{34kW\cancel{-hr}}{\cancel{15min}}\times \frac{(4)\cancel{15min}}{1\cancel{hr}}=136kW$
$34 \times4=136$
Data received in kW
Measured by hour
Consumption ($kWh$) is equal to the sum of all your data.
Demand ($kW$) is equal to your max measurement of that day.
Measured in 30 minute Intervals
Consumption ($kWh$) is equal to the sum of all your data divided by 2.
Demand ($kW$) is equal to your max measurement of that day.
Measured in 15 minute Intervals
Consumption ($kWh$) is equal to the sum of all your data divided by 4.
kW measured each 15 minutes, the sum divided by 4 is equal to kWh.
Demand ($kW$) is equal to your max measurement of that day.
Easy peasy.
Great, now you may be wondering, “Well, how do I get my data?” Great question!
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