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Power And Demand

Jenn Maa
Demand Management 101

Understanding power of a time interval:

Instantaneous power (demand)
 

The instantaneous power (or instantaneous demand, or instantaneous load) is the quantity of power that something is using (or generating) at any one moment in time. Instantaneous power is measured in kW (kilowatts).

ex: Put your laptop on standby and its instantaneous power will drop immediately. Bring it back to life and its instantaneous power will rise immediately.

If, at any particular moment, everything in your home is switched on, your home might be using 20 kW of power. That's 20 kW of instantaneous power. If, at any particular moment, everything in your home is switched off, your home should be using 0 kW of power. That's 0 kW of instantaneous power.
The instantaneous power of most homes varies constantly.

 

Average power
 

The average power represents the amount of instantaneous power used over a specific period of time (e.g. 30 and 60 minutes). It is measured as kWh(kilowatt hours).

Average power enables you think of complicated things, like entire homes, as if they were simple things, like light bulbs...

The instantaneous power of a typical home varies all the time. If you try to monitor instantaneous power you get lost in the noise. And figures of energy consumption are meaningless unless you know the length of the periods that they were measured over. But average-power figures smooth out the constant fluctuations of instantaneous power, and make it possible to calculate to the rolling average that is read by the utility.

How Demand Rate Usage is Determined:   

Using the speedometer analogy; instantaneous demand is how fast you are going at this second. Average demand is the average speed you traveled over time, such as 30 minutes or 60-minutes.

What utilities do is capture the HIGHEST (of peak) demand for the period during on-peak hours. If you drove an average of 45mph the first hour, 50mph the second hour, 55mph the third hour, your highest average speed for the 3 hours is 55mph.

 

Your Monthly Demand Charge is based on the highest Average Demand measured in an interval based on the utility.

Inergy Demand Manager's are able to calculate at a very close approximation of your Utility Rate and Specifications, and help you from going over a Set Demand Limit.

This limit is initially set up based on general home and energy usage information, and can be tailored to suit your household best.

APS:

APS on-peak hours are 3-8pm M-F. The meter looks at the end of each on-peak hour to see if the demand over the hour was higher and if so, that becomes the new peak demand number (until reset).

Example:
4pm 4kWh used
5pm 5kWh used
6pm 5.5 kWh used
7pm 6.0 kWh used
8pm 6.5 kWh used

Since APS uses a 60-minute demand window they look at the accumulation over the hour. In this case the peak demand would be 6.5kW.

 

SRP:

SRP uses a 30-minute interval. Their meter looks at the :30 and :00.
They look at how much electricity was used during the 30-minutes period, which is multiplied by 2 to achieve the Average kilowatts per hour (kWh).  

1:30pm 2kWh used (times 2) 4kWh of 4 kW average
2:00pm 2.5kWh used (times 2) 5kWh or 5kW average
2:30
3:00
..
..
6:00pm
6:30pm
7:00pm 3.5kWh used (times 2) 7kWh or 7 kW average
7:30pm 3.0kWh used (times 2) 6kWh or 6 kW average
8:00pm 3.6kWh used (times 2) 7.2kWh of 7.2 kW average
The highest 30-minute demand is 7.2kW

We are always happy to help.
Contact us at: 
support@inergysystems.com

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Last Modified: Last Year
Last Modified By: jmaa
Type: INFO
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