New user - not sure what I need

Hi, Newbie here looking for some advice as i’m finding the info on the website a bit overwhelming!!!

I’m in the UK, I have solar PV panels and also a ‘solar iBoost’ unit (Solar iBoost+ - UK's Favourite PV Immersion Controller) which is meant to divert surplus electricity to an electric heating element in my hot water tank.(Water is normally heated by the kerosene boiler.)

I’d like to be able to see my power generated, power consumed and what surplus power is being used to heat water.

I don’t want to spend more than needed for this, but i’m confused if i can manage this using eMonTx only or if i need the eMonPi.

Also the water tank and solar iBoost unit are not next to the meters and fuse box so not sure if that will cause problems. i could run a cable through the loft if needed but it would need to be approx 8 meters long.

Any advice on how/if I can do this gratefully received!!!



Hey Steve.

Is your immersion heater (and solar iBoost) fed from a dedicated circuit breaker in the consumer unit? if so, that would be the place to measure it.

If that is the case what I would suggest is the following:

One emonTX at the fuse box. It supports up to 4 current clamps, so place one on the main incoming power, one on the PV circuit and one on the immersion heater circuit. You will need a double socket to plug that into, next to the consumer unit.

One emonBase, at your broadband router. Plug it straight in to the router, this is a robust connection which won’t ever need configuring or changing if you have to change the router or wifi password.

If you also want to look at tank temperature, get an emonTH as well and put the external probe into a tank pocket or against the surface under the insulation.

Bear in mind that the iBoost does tell you daily and weekly energy “diverted” on its display if that’s all you want to know…

Just my thoughts as a user, hope it helps.

Welcome, Steve, to OEM.

Can you confirm that, because the way I read your post, and even though you didn’t say it, the immersion heater (hence the iBoost) is fed off the ring main.

You’re asking for three quantities to be measured. If that’s the case, then an emonPi on its own may be no good for you, because it only measures two by directly measuring current. An optical pulse sensor might be useful, but only on the generation meter - it’s no good on the grid meter because it can’t indicate exported energy - or if it does, it can’t distinguish export and import. And it’s of limited use for indicating power (as distinct from energy) because you don’t know the pulse rate until after the next pulse has arrived!

So it comes down to where you can measure what.

Where does the PV infeed meet the rest of the house wiring? This is fairly crucial information.

What cable did you have in mind? If it’s an extended c.t. (“Clamp” appears to be a mis-translation - it’s certainly not an English term for a current transformer) cable (say 6 mm diameter ‘microphone’ cable), can you run that from your iBoost to where the meters are - presuming both grid and generation meters are together? Then an emonTx there (as Evan says) is probably the best.

But if you’re happy with a pulse sensor on the generation meter, an emonPi there (no emonBase needed now) would give you what you want.

But whatever you end up with, an emonTx can’t function completely on its own. It needs either an ESP8266 Wi-Fi module to send the data either to or to your own server running emonCMS, or it can use its inbuilt ISM band radio to send the data to an emonBase or emonPi, and both of those use a Raspberry Pi as a server running emonCMS.

Of course you can do it. We’re not beaten very often. Your big problem (maybe you’ve not realised it yet) is the OEM system is very flexible and that this is partly why …

There is a lot here. Just take it in steadily, and please ask if anything isn’t clear.

My bad. Current clamp (colloquially) means this:


What I should have said was split core current transformer :slight_smile:

And to me, a clamp means this:
It’s only since I’ve been here that I’ve heard a c.t. referred to as a “clamp”. For about 40 years previously, it’s always been a c.t. or current transformer (in full). And those things in your picture always used to be called “clamp ammeters”, never “current clamp”.

And never to be confused with the other sort that I’m familiar with, a busbar clamp.

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Sorry for the delayed reply.
Thanks both for that useful information.
In answer to your questions, the immersion heater does appear to have it’s own switch in the fuse box and the solar PV infeed and meter are next to the regular meter.

I’ll do some more reading up on the emonTx. From what you both told me it is pretty much guaranteed that I’ll need it.


Hi Steve, I have a similar situation to you (4kW PV array, Solar iBoost smart switch, oil CH and HW and a bit of an open source newbie), and have recently installed an emon system to monitor generation, export, divert and consumption. But because of the distance between various circuits I have had to go down the route of 3 EmonTx and one emonPi (due in part because the EmonTx can handle more inputs than an emonPi). Not cheap, but it now produces the data that I was looking for so I am happy. I see that you are UK based; I’m in W Sussex.

Do you have wired internet available close to the consumer unit etc? In my limited experience, wi-fi was a bit of an issue, albeit now resolved through support from here and the shop.

Also, do you intend to “host” your data locally, or use Open Energy Monitor’s servers (for a very small annual fee)? For simplicity I opted for the latter, but might change things later.

Good Luck!


PS I have promised not to use the word “clamp” on here ever again :smile::smile::smile:

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So it does look as if you are going to locate everything near the consumer unit and meter. The big question that will settle whether you can get away with just an emonPi is, can you fit the optical pulse sensor to the generation meter and get a measure of the PV infeed that way? If you can, you should consider the emonPi. But bear in mind what a pulse actually means - it tells you a chunk of energy has just been fed in. Energy, not power.

And have you got access to the cable cores inside the consumer unit and enough space to put c.t’s on them? If you have single core meter tails, the Grid c.t. will go there. The doubtful one is the immersion heater.