FoxESS KH10 single phase inverter built-in CT feature

[sam2005]

The FoxESS KH10 single-phase hybrid inverter includes a built-in CT meter. I would like clarification regarding the functionality of the built-in CT and the use of an external smart meter:

• Does the built-in CT measure both on-site power consumption and grid feed-in?

• If the built-in CT is capable of measuring power, what is the purpose of the separate meter ports on the FoxESS KH10?

• What additional features do we get by using a smart meter?

[Dave Foster]

It doesn't have a built in CT meter, it is supplied with a CT clamp that must be attached to the incoming live feed so that it can measure load, grid consumption etc..

A CT clamp is very simple to install and for most installations it is all that is needed, however a CT clamp is at best 1-2% accurate and worse so at low loads.
The main reasons that people fit RS485 meters such as the Chint or Eastron is that a) they are slightly more accurate, b) they can be run reliably over much longer distances than a CT cable.

[sam2005]

I am grateful for your response.

Could you kindly clarify whether a rate of 1% to 2% indicates accuracy or an error rate? Moreover, if the accuracy is only 2%, what practical applications might it have?

I understand that smart meters also utilize CT clamps for measuring current and voltage. I also have a Sungrow_S100, which also employs CTs.

I am considering installing a KH10 with an EQ4800 Battery. Therefore, I am curious whether I should install a smart meter like DDSU666 or simply utilize the built-in one.

[Dave Foster]

The CT clamp accuracy is specified by it's accuracy class and also a phase error - but it's important not to get hung up with their accuracy as these can never be precise, they can be affected by proximity to other CT's and they do not measure power factor. This is simply a tool that the inverter uses to balance the load which will be dynamically changing all the time (and the inverter measures it and responds to it to achieve balance).

If you have a smart meter fitted by your supplier that is the absolute bench mark as it will be used for the suppliers billing, and that will never use CT clamps for it's measurement - it will be direct wired and takes power factor into account.

My usual advice is if you don't need to fit a meter because the distance between the inverter and your incoming supply is reasonable (less than 20 meters, ideally less than 10) then don't go to the additional expense and disruption from fitting an RS485 meter.

And just to clarify your last statement, it isn't built in, this is an external clamp that is supplied with the inverter that has to be clipped to the live feed from your supply and it feeds a balanced pair which is measured by the inverters CT input.

[sam2005]

I appreciate your clarification.

I now understand that the CT is not entirely precise and primarily serves the purpose of load balancing.

As I'm considering joining VVP and occasionally feed-in traffic goes negative during the daytime, so I'm looking for a way to halt the feed-in while ensuring your inverter continues to generate sufficient electricity to meet your household's needs. I think a KH inverter with a CT clamp might be a suitable solution. No need to add an extra RS485 smart meter.

Also, when I said the smart meter DDSU666, it also utilizes a CT clamp. There is no hard-wiring.

[Dave Foster]

I suspect our terminology for the 'smart' meter is different here in the UK - our 'smart meter' is the meter provided by the energy supplier to measure how much energy you use, whereas the RS485 meter I mention is indeed the Chint DDSU666.

The Chint meter has 2 installation options, either with or without CT clamps - but if you are installing the CT clamp version then the only advantage is the greater cable length between it and the inverter supplied CT clamp.

The KH inverter supports DRM which would let you restrict export based on tariff and you can set the export limit remotely which would also allow you to change the export based on tariff.
I'm not familiar with it myself but you can also link your inverter with Amber to manage your system https://help.amber.com.au/hc/en-us/arti ... SmartShift

[sam2005]

I am considering joining Amber VPP, and they said a smart meter, such as a DDSU666, is required to facilitate solar curtailment. Please see the attached image below from Amber.

I am just curious as to why additional energy monitoring devices, like the DDSU666, are necessary when a KH inverter equipped with a CT clamp appears capable of providing similar functionality.

I appreciate your insights on this matter.

[Dave Foster]

I'm really not sure why that is, the KH can certainly do what it needs with just a CT clamp - the only thought I would have is that when they say consumption meter, they may not need it for KH control, rather they need it as an energy counter they can access so they have an independent figure of how much electricity you are using (which is a bit like the 'smart meter' we have here in the UK).

[WyndStryke]

...
I'm not familiar with it myself but you can also link your inverter with Amber to manage your system https://help.amber.com.au/hc/en-us/arti ... SmartShift

Just an aside, but E-on are doing a pilot with Amber (E-on Next Solar Max tariff) in the UK. From the description it sounds like a hybrid of Agile and Intelligent Flux. Only 1000 people, and Fox isn't yet listed as an option. I've put myself on the waitlist but I suspect the 1000 slots will probably disappear before I can join. I'm guessing it is controlled via the cloud rather than via modbus, in which case I should be able to use HA to monitor (and maybe override at times) what it is doing. Don't know if there'll be an API which could be picked up on the HA side (since I think it would be useful to be able to ingest the pricing).