Power of Ten Multiplier

Green Button data units are based on international norms as well as regional units.  Whenever possible, the units use the most-base level of each unit.

For example, watts (W) are used instead of kilowatts (kW).  However, the kilowatt and the kilowatt-hour (kWh) are the typical measurements for billing purposes (for residential and small businesses, at least).

Further, the sent values (value) are represented as integers in the XML data fields of Green Button outputs—not represented as decimals or as floating-point values.

A power-of-ten multiplier is used to represent that the values being sent are different from the unit of measure.


powerOfTenMultiplier

The ESPI standard has a scaling device called the powerOfTenMultiplier, which as its name implies, handles the adjustment of base units to desired units.

What’s tricky is knowing when the multiplier should be applied.

When a Data Custodian (utility, aggregator, other provider of usage data) loads data into a Green Button output file or stream to share with a consumer or their agent, they include the unit of measure (uom), the measured or calculated (and then sent) value (value), and often a multiplier (powerOfTenMultiplier) to adjust their value to something other than the unit of measure.


For a ReadingType, a file/stream of usage data may have something like this:1

<content>
  <espi:ReadingType>
    <espi:accumulationBehaviour>12</espi:accumulationBehaviour>
    <espi:commodity>1</espi:commodity>
    <espi:flowDirection>1</espi:flowDirection>
    <espi:intervalLength>300</espi:intervalLength>
    <espi:kind>12</espi:kind>
    <espi:phase>129</espi:phase>
    <espi:powerOfTenMultiplier>3</espi:powerOfTenMultiplier>
    <espi:uom>72</espi:uom>
  </espi:ReadingType>
</content>

In this example, there are several fields/elements/tags that we’ll use for other examples, so let’s go into them here:

  • accumulationBehaviour is set to an enumeration of “12” — which means “instantaneous”: “Typically measured over the fastest period of time allowed by the definition of the metric (usually milliseconds or tens of milliseconds.)
  • commodity is set to an enumeration of “1” — which means “electricity Secondary Metered”: “All types of metered quantities. This type of reading comes from the meter and represents a ‘secondary’ metered value.
  • flowDirection is set to an enumeration of “1” — which means “forward”: “‘Delivered,’ or ‘Imported’ as defined 61968-2. Forward Active Energy is a positive kWh value as one would naturally expect to find as energy is supplied by the utility and consumed at the service. Forward Reactive Energy is a positive VArh value as one would naturally expect to find in the presence of inductive loading. In polyphase metering, the forward energy register is incremented when the sum of the phase energies is greater than zero.” (where “61968-2” refers to the IEC 61968-2 System interfaces for distribution management – Part 2: Glossary).
  • intervalLength is set to a value of “300” — which means 300 seconds for the particular interval measurement (five minutes).  For most residential applications, this value is usually “3600” (one-hour intervals).
  • kind is set to an enumeration of “12” — which refers to a MeasurementKind of “energy” (since currency, temperature, and other things could be the measured value).
  • phase is set to an enumeration of “129” — which refers to a PhaseCodeKind of “AN”: “Phases A to neutral.
  • powerOfTenMultiplier is set to a value of “3” — which means the actual value (let’s call it: V) equals the sent value <espi:value>4321</espi:value> (let’s call the sent value: VS) — multiplied by ten-to-the-3rd power:  V = VS × 103.  We’ll look at an example with a multiplier of “3” shortly (below).
  • uom is set to an enumeration of “72” — which means “Wh”: “Real energy, Watt hours, Wh.

The uom unit is used for the base unit-of-measure for readings of ReadingType in combination with the powerOfTenMultiplier to specify the actual value as it relates to the unit of measure.


Kilowatt-Hours v. Watt-Hours

Using kWh and Wh as examples, it’s easy to see how the value from the Data Custodian could be sent in different ways but the received actual value will be the same. 

✏️ — Before we proceed, please note the below example value of 4321.000 kWh is being displayed to you in YOUR locale numbering format2, therefore you should be reading this number as four thousand, three hundred, twenty-one kilowatt-hours.  If you are reading it as something other than that, your locale settings in the browser you are using are set incorrectly.

EXAMPLE… 

If a Data Custodian wanted to denote that a consumer used 4321.000 kWh — which is (four thousand three hundred twenty-one kilowatt-hours) in a given interval, they could send either of the following:

<espi:value>4321</espi:value>
...
<espi:powerOfTenMultiplier>3</espi:powerOfTenMultiplier>
<espi:uom>72</espi:uom>  /* a unit of “Wh”  */

or the equivalent: 

<espi:value>4321000</espi:value>
...
<espi:powerOfTenMultiplier>0</espi:powerOfTenMultiplier>
<espi:uom>72</espi:uom>  /* a unit of “Wh”  */

    
Either one would provide the receiver with an actual value of 4321.000 kWh (four thousand three hundred twenty-one kilowatt-hours).

The uom, however, is Wh (watt-hour) — there is no kWh (kilowatt-hour) option in the Green Button data format.  That lack of scaled base values prevents a receiver from having to handle multiple unit types for the same measured quantities of a particular resource.  The Third Party needs only to know that the sent value provided (VS) will be scaled by the powerOfTenMultiplier to know the actual value (V) in the provided uom unit type; then, is can be displayed as Wh or kWh as the application desires.


So, using our example, let’s first show our formula with a powerOfTenMultiplier of “3” and a sent value of “4321”: 

V = VS × 10x
V = 4321 × 103
V = 4321 × 1000
V = 4321000
V = 4321000.000 Wh (four million three hundred twenty-one thousand watt-hours)

That’s the same as 4321.000 kWh (four thousand three hundred twenty-one kilowatt-hours).


If we use a powerOfTenMultiplier of “0” instead with a sent value of “4321000”, we get:

V = VS × 10x
V = 4321000 × 100
V = 4321000 × 1
V = 4321000
V = 4321000.000 Wh
(four million three hundred twenty-one thousand watt-hours)

… the same actual value as above: 4321.000 kWh (four thousand three hundred twenty-one kilowatt-hours).


What if the powerOfTenMultiplier was “−3” with a sent value of “4321000”?  In that case, we would get:

V = VS × 10x
V = 4321000 × 10(−3)
V = 4321000 × 0.001
V = 4321
V = 4321.000 Wh
(four thousand three hundred twenty-one watt-hours)

… a very different actual value from what’s above: 4.321000 kWh (four and three hundred twenty-one thousandths kilowatt-hours).

The value field is a 48-bit integer, so this last example shows where the powerOfTenMultiplier is critical to the value to accurately express the actual value

“4.321” cannot be carried in a value field because it is not an integer.  There can be no decimal in the value field.


Often, the actual scaled value can be more-or-less verified by understanding the value, the uom, and the intervalLength, but out of context it may still be difficult to know if the actual scaled value is correct — especially if it still fits within expectations regardless of scaling direction.  When implementing, as a Data Custodian, it is important to be consistent and:

check the output of real data to be sure you are properly conveying what’s actually desired. 


    

Need more help with this?  Check-out our Technical Education offerings.


For examples of Atom’s relationship to ESPI for Green Button data,
see our page about Atom & ESPI.

  1. See the page on Atom & ESPI to understand the “espi:” notation herein.
        
  2. Because “thousands” and “decimal” placeholders vary in different countries and regions, please note that the examples here use your browser’s LOCALE information to format the example results into a locale-specific representation of numbers.  Therefore, in our examples that use a comma for marking thousands and a period (full-stop character) for marking decimals (like this: 9,876.543 kWh), you may see 9876.543 kWh — which is nine thousand eight hundred seventy-six and five hundred forty-three thousandths in any case.