WISH LIST EmonCMS Feed In Tariff

Would it be possible to add a visualisation that covers feed in tariff for PV

I.e supply it with usage from the grid clamp and output from the pv clamp

give it feed in tariff money figures for generation and the export tariff and have it all display somehow to give a rough idea of how much money is

A: Generated

B: Made from Export

C: Saved in offset from grid use?

I.e the generation can only be counted as a saving if the grid load is lower that the pv output but it is a saving and not a cost if you see what im trying to say!

Does that make sense ?


pb66's picture

Re: WISH LIST EmonCMS Feed In Tariff

Are you specifically looking for a custom visualation or would an "amount saved" feed for you to base a visualisation on suffice?

I have feeds for SolarUse SolarUseToday SolarUseTotal SolarSaving SolarSavingToday SolarSavingTotal these are all derived from the calculation of grid input > allow negative only > add solar input = SolarUse, basically solar produced but not exported must have been used. Each can be displayed in Kw/hrs or multiply by feedin-tariff rate for monitary values.

Regards the export v generation amounts do you have an export meter or do you just get a flat 50% of generated like me?
I found it easier to just add 50% of the export unit price to the generated unit price and use that for 100% of generated it works out exactly the same. 


dod's picture

Re: WISH LIST EmonCMS Feed In Tariff

Hi Paul,

It would be nice to have a custom vis that you input export and generation tariffs data into.

It would be nice to see your feeds, my own feeds are almost there but not quite.

This is what I have but I didnt figure out how to do FIT

And I dont have an export meter just 2 generation meters




pb66's picture

Re: WISH LIST EmonCMS Feed In Tariff

Here are some screen shots of my current inputs, feeds and some calcs, unfortunately the process lists in emonCMS do require a bit of deciphering because the inputs are not id'd by description, but by input number without a node id. Ignore the Amps feeds they will be deleted in time I only use them when calibrating new software/hardware.

What you may find more useful is the screenshot of my emonCMS calcs backup spreadsheet I made not so long ago when I had a bit of a scare and thought I might lose all my input/feed data, (although I'm pleased to say I didn't) .


MrOrange's picture

Re: WISH LIST EmonCMS Feed In Tariff

Hi Paul - Could you please explain your cost calculations further?  I assume you need to account for the frequency of the input updates in the calculations (ie. The fraction that a 10s represents from an hour). 

So if we log every 10s (360 logs an hour) and my unit cost is $0.23 my calculation would be;

(unit cost / 1000) / 360 = cost per Watt per 10s

So in emoncms;

input x 0.00000063889

Doing it this way based on real time usage seems like it will be quite inaccurate as sometimes the log frequency flucatuates.

Is that correct? Or do I have a major flaw in my understanding of emoncms data logging?

Either way I think it would be extremely useful if we could use feed values in processing. That way we can simply use kWh * unit cost

pb66's picture

Re: WISH LIST EmonCMS Feed In Tariff

As emoncms already handles both power (kw) and energy (kw/h) it is possible to log amount spent and rate of spend by multiplying by unit price. you don't need to factor in any update rate or time references if you are charged a flat rate all day everyday then that unit price can be just hard-coded into your calc's

If you look at the solar input processing steps 18 to 25, these steps will work for costs as well, As the processes are designed for power & energy there is some "leveling" math involved, here are those steps explained and altered for your purpose

18 & 19  allow negative & allow positive resets the chain to zero

20         +input "grid"

 -          allow positive (required to exclude export unless you have a net usage tariff)

21         x  0.023 (23 cents per kw/hr x 0.001 = 0.023 cents per w/hr)

22         log to feed "MyRunningImportCostPerHour" logged/displayed in cents varies & with load

23         x 1000 (this is to counteract the in-built w to kw conversion in the "power to KWh/d" function)

24         Power to KWh/d feed "MyImportCostToday" logged in cents

25         Power to Kwh feed "MyTotalImportCosts" logged in cents


If you have multiple tariff rates for various times that is a different matter which has to be tackled another way.

there are so many different scenarios that one size definitely won't fit all, so if this doesn't work let us know a bit more about your tariff types, system and what you want to log.


MrOrange's picture

Re: WISH LIST EmonCMS Feed In Tariff

Thanks Paul - no you've got it in one. I do just have a flat rate here so this example works well.

I still can't quite get my head around how emoncms is actually calculating energy usage then but I really appreciate the time you've taken to explain this example. My understanding of the system is getting better with every day!

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