UK Supplier or Import?

Hi folks, Newbie to the forum.
I’m UK based, Looking to have a solar PV system with battery storage installed in the next month or so.
Would like to be able to have a fairly granular view of my useage, generation and feed in to the grid. I’m looking at the Openenergymonitor and the Iotawatt. Iotawatt seems to fit the bill from what I’m reading.
Where is the best place to buy from for delivery to UK please?
Also is there a central place to find idiots guides to installing and setting up the system?
Many thanks.

Order at (generic kit) and separately order UK plug USB power supply and AC adapter from Farnell there in the UK.

Installation guide at

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Single phase or 3 phase?

@overeasy Thanks for that much clearer now.

@philrob Single Phase.

Getting my mind around it now. Thanks for the input.
Just a question on the best CT’s for use in a cramped UK Dist Panel.
The circuits I have/want to monitor are:

Main Grid Feed - 100A
Cooker - 40A
Ring Mains - 3 x 32A
Lighting - 2 x 6A
Water Heater - 16A
Solar Feed - ?

IoTaWatt only seem to sell 100A CT’s.
Is there a better supplier that sell more suitable CT’s available in the UK?

There are 50A CTs available in the Generic kit and also in the “Current Transformers” dropdown tab.

I can’t say if they will fit into your Panel.

Thanks overeasy, 8 found the drop-down.

Sorry to keep asking what may appear to be daft questions.
Will the 50A CT’s be suitable for the low current lighting circuits?
If not is there a more suitable one available anywhere?
Or, could I merge all three lighting circuits into one CT? i.e. pass all the leads through one CT (assuming they fit).
Or, would it be better to not bother with the low current lighting circuits and just calculate them from the main feed - the sum of the other circuits?
What size CT would be best suited to my PV feed?

Single phase makes things much easier and frees up a lot of inputs on the iotawatt.

Your solar will be max 4kW (unless the rules have changed). So 50A CT should be fine. P=VA so A = panel rating/230.

If you are looking for power hogs then putting the three lighting circuits through one ct should be fine (lighting isn’t likely to eat much power.) If usage is higher than expected you can rearrange the circuits to check one at a time.

It is worth subscribing to when you have your solar up and running. Mine reports how much money I have saved by using my own power. It’s an old system and I get paid deemed export of 50% of what I generate irrespective of how much I actually export.

If it is a normal uk distribution board you may have a challenge with the CTs. If you have a problem, Wago do a db relocation unit that might allow you to move the db while running the cables through a box that can hold the CTs. Technically moving a DB needs an electrician and a certificate afterwards.

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Thanks philrob, so would my thoughts about not directly monitoring the lighting circuits and using the total feed minus the sum of all the other circuits work? It would save space.

It Should do.

There is a difference between data, information and action.

Iotawatt is fantastic at providing data. The analysis tools are good a drilling down if there is a ‘funny’.

Storing the data in influx (or pv output) and adding your tariff then reporting cost on a dashboard (home assistant or grafana) will hopefully allow action. With energy hitting 40 pence per kw in the uk this autumn finding and fixing powerhogs is going to be important.

Have fun.

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Last question (I hope).
What is the best source for solid core CT’s for use with IoTaWatt, here in the UK? prefferably plug and play but I don’t mind soldering plugs on if I must.

Edit: Sorry, I just spotted that you wanted solid core CTs which shouldn’t be a problem but my order was for clip-on CTs. Also, I ordered without 3.5mm plugs as I wanted to use right angle ones which I sourced separately via Ali Express.

I’m in the UK too, in Chester. I have recently ordered YHDC / Poweruc CTs from Amy in their Polish office: Amy Wang: contact at

I have purchased:


Let me know if you need any help.

Regards, Steve

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Hi there, I’m in UK too and want to do exactly the same as you for my PV system with hybrid inverter to batteries and also a second string inventor. Did you source a Iotawatt kit?

Hi, I bought my IoTaWatt some years ago from OpenEnergyMonitor which I don’t think is possible now. My recommendation would be to order direct from IoTaWatt and is what I would do if ordering now, probably with the higher quality CTs Bob sources. All of my CTs are the YHDC ones.
Rgds, Steve

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Recently purchased mine direct from IotaWatt complete with CT’s. Sourced power supplies locally though. The only downside was I got stung for £53 import duty by UK Customs.