# Node-red-contrib-watt2kwh
**URL:** https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157
**Category:** Share Your Nodes
**Created:** [11 July 2019 09:41 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157 "2019-07-11T09:41:24Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [11 July 2019 09:41 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/1 "2019-07-11T09:41:24Z")
I've just published v0.1.0 of [node-red-contrib-watt2kwh](https://flows.nodered.org/node/node-red-contrib-watt2kwh) which is specifically written to convert power (watts) to energy (kWh).
It carries out the conversion by measuring the interval between consecutive inputs, and multiplying it by the power value - **interval x power = energy**.
The output is then scaled to deliver units of Joules, Watt hour, Kilowatt hour or Megawatt hour which is selectable in the node's configuration.
Hope it's of use!
---
### Author:  [@SuperNinja](https://discourse.nodered.org/u/SuperNinja)
#### Post date: [11 July 2019 10:10 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/2 "2019-07-11T10:10:53Z")
I test it immediately for my photovoltaic production 😛
---
### Author:  [@Urs-Eppenberger](https://discourse.nodered.org/u/Urs-Eppenberger)
#### Post date: [11 July 2019 12:56 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/3 "2019-07-11T12:56:28Z")
Installed and worked. I use it for my PV production and house consumption.
The node replaced a rather cumbersome flow with global variables.
Thanks.
---
### Author:  [@x375993](https://discourse.nodered.org/u/x375993)
#### Post date: [12 July 2019 10:49 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/4 "2019-07-12T10:49:11Z")
Hi Paul...
Just a small coding trick to compact those big switch-statements.
> formats = {"j":1e-3, "kj": 1, "wh": 3.6}
> output = formats["jk"]
---
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [12 July 2019 18:52 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/5 "2019-07-12T18:52:34Z")
> [@x375993](#):
>
> Just a small coding trick
So.. instead of the switch statement, use this instead?
```auto
const formats = {"j":1e-3, "kj": 1, "wh": 3.6, "kwh": 3600, "mwh": (1e3*3600)};
this.output = formats[config.format] || 0;
```
It seems to work ok, is there a trade off?
---
### Author:  [@x375993](https://discourse.nodered.org/u/x375993)
#### Post date: [12 July 2019 19:53 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/6 "2019-07-12T19:53:55Z")
There are many ways of doing things - no one is more correct than others.
The advantage with the associative array is that if you do lookups with many key-value pairs then your code will be much more compact this way.
I don't think there are any trade offs.
---
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [12 July 2019 19:56 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/7 "2019-07-12T19:56:44Z")
In that case I'll update the node shortly
Thanks @x375993 Alex.
---
### Author:  [@x375993](https://discourse.nodered.org/u/x375993)
#### Post date: [12 July 2019 20:13 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/8 "2019-07-12T20:13:15Z")
Btw... you can also do it with your timeunits
> const unitfact={"secs": 1, "mins": 60, "hours": 3600}
> this.maximum \*= unitfact[config.maximumunit]
---
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [12 July 2019 20:14 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/9 "2019-07-12T20:14:46Z")
Yes, already updated it, thanks
---
### Author:  [@Teryeahh](https://discourse.nodered.org/u/Teryeahh)
#### Post date: [23 November 2021 15:44 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/10 "2021-11-23T15:44:45Z")
Hi. How can i use this in more than one flow? Og i use it in more than one i get the same values out of every watt2kwh node..
---
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [23 November 2021 16:35 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/11 "2021-11-23T16:35:15Z")
> [@Teryeahh](#):
>
> i use it in more than one i get the same values out of every watt2kwh node..
If you are feeding in the same data, I would expect every watt2kwh to produce the same output.
Can you post a flow to demonstrate the problem, using inject nodes & debug nodes, because I'm not really sure what you are describing.
---
### Author:  [@Teryeahh](https://discourse.nodered.org/u/Teryeahh)
#### Post date: [23 November 2021 19:15 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/12 "2021-11-23T19:15:47Z")
These two flows. It has different input values. but still the watt2kwh gives the same output
---
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [23 November 2021 19:47 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/13 "2021-11-23T19:47:31Z")
Try adding a debug node to each of the watt2kwh outputs, and show a screenshot of your debug panel (like below)
If you add names to the debug nodes, we can see which watt2kwh produced it.
---
### Author:  [@RichdeCrep](https://discourse.nodered.org/u/RichdeCrep)
#### Post date: [24 November 2021 03:20 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/14 "2021-11-24T03:20:36Z")
Thanks Paul,
That's a simple great tool that I needed and is in good use now.
Thanks again
Rich
---
### Author:  [@Walt\_Dod](https://discourse.nodered.org/u/Walt_Dod)
#### Post date: [22 October 2022 03:04 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/15 "2022-10-22T03:04:47Z")
Hello,
I have been testing the watt2kWh node, I cannot figure out the following :
I downloaded the flow advised by Paul-Reed and injected zero kW every second. The stored result is not zero...
Can you please have a look ?
Kind regards,
Walt
```auto
[
{
"id": "72985628cd69b236",
"type": "function",
"z": "4fe759c01b309d0a",
"name": "Store kwh",
"func": "var inputVal = msg.payload;\nif (inputVal == \"reset\"){\n flow.set(\"energyVal\",0); \n } else {\nvar savedVal = flow.get('energyVal')||0;\nsavedVal += inputVal;\nflow.set(\"energyVal\",savedVal);\nmsg.payload = savedVal;\nreturn msg;\n}",
"outputs": 1,
"noerr": 0,
"initialize": "",
"finalize": "",
"libs": [],
"x": 620,
"y": 2520,
"wires": [
[
"2f7c403dc696f005"
]
]
},
{
"id": "f0342efc1df3ec36",
"type": "watt2kwh",
"z": "4fe759c01b309d0a",
"format": "kwh",
"maximum": "60",
"maximumunit": "mins",
"name": "",
"x": 380,
"y": 2480,
"wires": [
[
"72985628cd69b236"
]
]
},
{
"id": "8a6d0f53c496353c",
"type": "inject",
"z": "4fe759c01b309d0a",
"name": "",
"props": [
{
"p": "payload"
}
],
"repeat": "1",
"crontab": "",
"once": false,
"onceDelay": 0.1,
"topic": "",
"payload": "000",
"payloadType": "num",
"x": 180,
"y": 2540,
"wires": [
[
"f0342efc1df3ec36"
]
]
},
{
"id": "2f7c403dc696f005",
"type": "debug",
"z": "4fe759c01b309d0a",
"name": "",
"active": false,
"tosidebar": true,
"console": false,
"tostatus": false,
"complete": "payload",
"targetType": "msg",
"statusVal": "",
"statusType": "auto",
"x": 910,
"y": 2520,
"wires": []
}
]
```
---
### Author:  [@Walt\_Dod](https://discourse.nodered.org/u/Walt_Dod)
#### Post date: [22 October 2022 03:24 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/16 "2022-10-22T03:24:44Z")
I further my point : 2 identical flows, one injecting 1 kW/s, the other 2 kW/s. they give the same energy stored. Please help !
```auto
[
{
"id": "72985628cd69b236",
"type": "function",
"z": "4fe759c01b309d0a",
"name": "Store kwh",
"func": "var inputVal = msg.payload;\nif (inputVal == \"reset\"){\n flow.set(\"energyVal\",0); \n } else {\nvar savedVal = flow.get('energyVal')||0;\nsavedVal += inputVal;\nflow.set(\"energyVal\",savedVal);\nmsg.payload = savedVal;\nreturn msg;\n}",
"outputs": 1,
"noerr": 0,
"initialize": "",
"finalize": "",
"libs": [],
"x": 620,
"y": 2520,
"wires": [
[
"2f7c403dc696f005",
"62fc58e95b92ba3f",
"75c409b68ba81ef1"
]
]
},
{
"id": "f0342efc1df3ec36",
"type": "watt2kwh",
"z": "4fe759c01b309d0a",
"format": "kwh",
"maximum": "60",
"maximumunit": "mins",
"name": "",
"x": 380,
"y": 2480,
"wires": [
[
"72985628cd69b236"
]
]
},
{
"id": "8a6d0f53c496353c",
"type": "inject",
"z": "4fe759c01b309d0a",
"name": "",
"props": [
{
"p": "payload"
}
],
"repeat": "1",
"crontab": "",
"once": false,
"onceDelay": 0.1,
"topic": "",
"payload": "1000",
"payloadType": "num",
"x": 180,
"y": 2540,
"wires": [
[
"f0342efc1df3ec36"
]
]
},
{
"id": "2f7c403dc696f005",
"type": "debug",
"z": "4fe759c01b309d0a",
"name": "",
"active": false,
"tosidebar": true,
"console": false,
"tostatus": false,
"complete": "payload",
"targetType": "msg",
"statusVal": "",
"statusType": "auto",
"x": 910,
"y": 2480,
"wires": []
},
{
"id": "400ccdd38c87a58a",
"type": "function",
"z": "4fe759c01b309d0a",
"name": "Store kwh",
"func": "var inputVal = msg.payload;\nif (inputVal == \"reset\"){\n flow.set(\"energyVal\",0); \n } else {\nvar savedVal = flow.get('energyVal')||0;\nsavedVal += inputVal;\nflow.set(\"energyVal\",savedVal);\nmsg.payload = savedVal;\nreturn msg;\n}",
"outputs": 1,
"noerr": 0,
"initialize": "",
"finalize": "",
"libs": [],
"x": 620,
"y": 2640,
"wires": [
[
"6c9caf2dc266bf9a",
"844083559b2e28ed",
"ac0beed0fc15f477"
]
]
},
{
"id": "38d80f0408df092e",
"type": "watt2kwh",
"z": "4fe759c01b309d0a",
"format": "kwh",
"maximum": "60",
"maximumunit": "mins",
"name": "",
"x": 380,
"y": 2600,
"wires": [
[
"400ccdd38c87a58a"
]
]
},
{
"id": "3fd908d1c1f43cda",
"type": "inject",
"z": "4fe759c01b309d0a",
"name": "",
"props": [
{
"p": "payload"
}
],
"repeat": "1",
"crontab": "",
"once": false,
"onceDelay": 0.1,
"topic": "",
"payload": "2000",
"payloadType": "num",
"x": 180,
"y": 2660,
"wires": [
[
"38d80f0408df092e"
]
]
},
{
"id": "6c9caf2dc266bf9a",
"type": "debug",
"z": "4fe759c01b309d0a",
"name": "",
"active": false,
"tosidebar": true,
"console": false,
"tostatus": false,
"complete": "payload",
"targetType": "msg",
"statusVal": "",
"statusType": "auto",
"x": 910,
"y": 2600,
"wires": []
},
{
"id": "844083559b2e28ed",
"type": "ui_chart",
"z": "4fe759c01b309d0a",
"name": "",
"group": "54ec15a15f8c33b7",
"order": 1,
"width": 0,
"height": 0,
"label": "2 kW/s",
"chartType": "line",
"legend": "false",
"xformat": "dd HH:mm",
"interpolate": "linear",
"nodata": "",
"dot": false,
"ymin": "0",
"ymax": "1",
"removeOlder": 1,
"removeOlderPoints": "100",
"removeOlderUnit": "86400",
"cutout": 0,
"useOneColor": false,
"useUTC": true,
"colors": [
"#1f77b4",
"#aec7e8",
"#ff7f0e",
"#2ca02c",
"#98df8a",
"#d62728",
"#ff9896",
"#9467bd",
"#c5b0d5"
],
"outputs": 1,
"useDifferentColor": false,
"className": "",
"x": 1070,
"y": 2640,
"wires": [
[]
]
},
{
"id": "62fc58e95b92ba3f",
"type": "ui_chart",
"z": "4fe759c01b309d0a",
"name": "",
"group": "54ec15a15f8c33b7",
"order": 1,
"width": 0,
"height": 0,
"label": "1 kW/s",
"chartType": "line",
"legend": "false",
"xformat": "dd HH:mm",
"interpolate": "linear",
"nodata": "",
"dot": false,
"ymin": "0",
"ymax": "1",
"removeOlder": 1,
"removeOlderPoints": "100",
"removeOlderUnit": "86400",
"cutout": 0,
"useOneColor": false,
"useUTC": true,
"colors": [
"#1f77b4",
"#aec7e8",
"#ff7f0e",
"#2ca02c",
"#98df8a",
"#d62728",
"#ff9896",
"#9467bd",
"#c5b0d5"
],
"outputs": 1,
"useDifferentColor": false,
"className": "",
"x": 1070,
"y": 2520,
"wires": [
[]
]
},
{
"id": "ac0beed0fc15f477",
"type": "ui_gauge",
"z": "4fe759c01b309d0a",
"name": "",
"group": "54ec15a15f8c33b7",
"order": 1,
"width": 0,
"height": 0,
"gtype": "wave",
"title": "2 kW/s",
"label": "W",
"format": "{{value}}",
"min": 0,
"max": "10000",
"colors": [
"#00b500",
"#e6e600",
"#ca3838"
],
"seg1": "",
"seg2": "",
"className": "",
"x": 1070,
"y": 2700,
"wires": []
},
{
"id": "75c409b68ba81ef1",
"type": "ui_gauge",
"z": "4fe759c01b309d0a",
"name": "",
"group": "54ec15a15f8c33b7",
"order": 1,
"width": 0,
"height": 0,
"gtype": "wave",
"title": "1 kw/s",
"label": "W",
"format": "{{value}}",
"min": 0,
"max": "10000",
"colors": [
"#00b500",
"#e6e600",
"#ca3838"
],
"seg1": "",
"seg2": "",
"className": "",
"x": 1095.6666259765625,
"y": 2560.666748046875,
"wires": []
},
{
"id": "54ec15a15f8c33b7",
"type": "ui_group",
"name": "test",
"tab": "9d3d0269bc96b7c1",
"order": 3,
"disp": true,
"width": "6",
"collapse": false,
"className": ""
},
{
"id": "9d3d0269bc96b7c1",
"type": "ui_tab",
"name": "Home",
"icon": "dashboard",
"disabled": false,
"hidden": false
}
]
```
---
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [22 October 2022 07:13 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/17 "2022-10-22T07:13:57Z")
I'll take a look, and reply back later.
---
### Author:  [@Paul-Reed](https://discourse.nodered.org/u/Paul-Reed)
#### Post date: [22 October 2022 08:18 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/18 "2022-10-22T08:18:56Z")
> [@Walt\_Dod](#):
>
> I downloaded the flow advised by Paul-Reed and injected zero kW every second. The stored result is not zero...
I think that the problem is that you have more than one flow accessing the same flow context described in your function nodes.
In the 3 flows that you have posted, all three use `flow.set("energyVal",savedVal);` so all three flows are being influenced by each other.
The `flow` context will work fine if you have just the one flow, but if you have more than one flow, you need to change the name of each flow context (`energyVal`, `energyValSolar`, `energyValHome`, etc) to stop them all overwriting each other.
Alternatively you could always use node context - `context.set("energyVal",savedVal);` instead.
Something like;
```auto
var inputVal = msg.payload;
if (inputVal == "reset"){
context.set("energyVal",0);
} else {
var savedVal = context.get('energyVal')||0;
savedVal += inputVal;
context.set("energyVal",savedVal);
node.status(savedVal)
msg.payload = savedVal;
return msg;
}
```
See [Writing Functions : Node-RED](https://nodered.org/docs/user-guide/writing-functions#storing-data)
---
### Author:  [@Walt\_Dod](https://discourse.nodered.org/u/Walt_Dod)
#### Post date: [22 October 2022 13:57 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/19 "2022-10-22T13:57:09Z")
Hi Paul,
Thank you for your answer !
I will test your solution, nevertheless, when the Zero injection flow is working alone, I get a non zero storing answer...
Regards,
W.
**Envoyé:** samedi 22 octobre 2022 à 10:29
---
### Author:  [@Walt\_Dod](https://discourse.nodered.org/u/Walt_Dod)
#### Post date: [22 October 2022 14:11 UTC](https://discourse.nodered.org/t/node-red-contrib-watt2kwh/13157/20 "2022-10-22T14:11:56Z")
Hi Paul,
Everything seems OK with the context solution.
I suggest you implement it definitively as it solves some structural deficiency without the user tinkering the code for each and every flow including the watt2kWh node.
Kind regards,
W.
**Envoyé:** samedi 22 octobre 2022 à 10:29
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