I've now successfully calibrated my Solar CT power measure using the Solar meter. That was easy enough.
Now how do I do the same for the grid CT power. Given that my grid CT will go both +ve and -ve on EmonCMS based on import or export, is it just a case of "Allow Positive" to be logged to a kwh Feed?
Re: Calibration of Grid CT measured power using EmonCMS
And another related question. Is it possible to give a feed an initial value. I want to enter my current meter reading to the kWh feed, so that I can then track any difference between it and my meter very easily.
Re: Calibration of Grid CT measured power using EmonCMS
The answer to your first question lies in exactly what you want to log, adding an allow positive will turn a nett use into a ever increasing use without factoring in any exports, however it may not precisely track the metered amount imported (billed) as any un-metered to'ing and fro'ing whilst "diverting" will still be included. Some would argue that the difference is quite small and near enough, which may well be true but it's not a calculated factor. Plus since the indiscrepancy increases with the diversion efforts, you indirectly wish the error to be as big as possible.
If I recall correctly you are using a MK2 in "normal" mode rather than anti flicker so I'm guessing the difference is quite minimal and as small as you are likely to get it. but if you try to adjust it out with multiplier bear in mind it is likely to be more accurate in the summer rather than the winter, as the error reflects the workload of the diverter modulating not the amount diverted.
To your second question, yes You could set up a simple "adjustment node" basically just set up your feeds as you would normally but also, using the input api via a browser create an input(s) that just "logs to feed" to your existing ever increasing "grid import feed" so that at any time you can "correct" the value by inputting the current meter reading via a browser.
Paul
Re: Calibration of Grid CT measured power using EmonCMS
I have a Type 2 Solar PV installation. So I would have thought that the Grid meter is only going forward when I am importing power. When I am exporting power it will just stop advancing.
Yes I do have the Mk2, but that too will be using the additional power that the solar pv is dumping into my consumer unit before it gets to the grid meter for export. So again, my assumption was that as long as I only add the positive power readings I should be able to match this to the grid meter.
Re: Calibration of Grid CT measured power using EmonCMS
The core concept of the PV diverters is effectively to import and export in such a way that it isn't detected by the meter so by very definition you have unmetered importing, but it is not obvious when observing the nett total as there is always corresponding "undetectected" exporting effectively canceling it out.
As I said above it should be minimal with the set-up you are running, I am effectively running in "anti-flicker" and can verify the led on my meter can be on (parked) for long periods of time, not registering any import whilst at the same time my emoncms will record the micro imports and exports. "nett grid" doesn't change but both "imported" and "exported" rise equally.
So on a really changeable & overcast day when the DHW tank doesn't reach temperature despite patchy PV generation, whilst I am confident I have not exported any PV emoncms could show I have exported 2kwh and imported 10kwh this would tell me I have actually imported 8kwh and the diverter has struggled to shuffle at least 2kw to the DHW, this is usually confirmed by a corresponding "diverted" of ~3kw. This all goes out the window in summer as I cannot use the PV fast enough so the (minimal) to'ing and fro'ing "export" is lost in the actual export.
Paul