Planning a new system, advice needed

Hi all,

I am very new to OEM so have a few questions to get me started.

Before I order the kit to get started I need to ensure I have the correct equipment to measure my system.

I have a Solar Edge PV installation with an immersion diversion (Immersun) connected.

I would like to monitor PV generation, energy diverted to the immersion and grid import/export.

In order to do this I see a few options;

  1. Purchase a emonPi with 2 clamps + AC-AC + DC 5v powersupply. 1 clamp on grid, 1 clamp on solar gen, ac-ac to ensure grid direction can be calculated, then import data from the solar edge api to read/report generation

  2. Purchase a emonPi with 2 clamps + AC-AC + DC 5v powersupply. 1 clamp on grid, 1 clamp on solar gen, ac-ac to ensure grid direction can be calculated, then add a emonTx V3 with another ac-ac (ac-ac but also powering unit) and 1 clamp to measure the solar generation

  3. Something else I have not considered/thought about/know about?

One thought I did have was, can the ac-ac on the emonTx V3 supply the reference voltage to the emonPi meaning I only need one ac-ac?

Any advice would be most welcome.



First, this is a clamp. In the UK, we use current transformers to measure current.

Secondly, Immersun is in voluntary liquidation, so you might want to think about the degree of support that is likely to be available in the future for your diverter.

As you’re in the UK, I assume a standard 240 V single phase installation.

The cheapest and simplest option will be no.1. but not connected as you suggest, because you’re getting the same value from 2 sources! I suggest one CT on the grid connection that will give you the nett import/export power, a feed from your inverter will give generation (but most likely not the quiescent consumption of the inverter during darkness - if that’s important to you, it will just appear as part of your house load) and one CT input to measure the diverted power. From those three values you can deduce the house consumption nett of diverted power, as well as the three input values.

If you add an emonTx, you have a total of 5 CT inputs. You can use the same a.c. adapter to both power/measure the voltage for the Tx and measure the voltage for the Pi. But I’m struggling to see why you need the extra current inputs - unless you can’t get a direct feed from the inverter, or unless you want to monitor separate circuits. (I suspect you didn’t write down what you meant for your option 2?)

Although this isn’t likely to influence you at the moment, both Robin Emley’s and MartinR’s diverters as published here can measure the diverted power - so something to have in the back of your mind.

This is almost spot on the same system I am installing right now. I have a Solar Edge PV system, and a Solar iBoost.

My idea is to have a standard OEM solar PV setup, monitoring house consumption and solar generation. And then use an Edimax smart plug to monitor how much is diverted to the iBoost. I managed to pick up a smart plug as a bargain in Maplin the other day.

By the way - you mention the solar edge API. Have you managed to get access to the actual API? I looked into it but it seemed that it was for installers. I keep meaning to email them about it but haven’t got round to it yet.

Thanks Robert for correcting my slang usage of the word “clamp”. :slight_smile:

Yes I am aware and have been in contact with the administrators over the likely future support for this device, which I might add at present they think is quite positive.

You would be correct.

Sorry yes a typo on my part. Yes one CT on the grid and other of the Immersun then use gen data from the SE API.

My thinking here was that in the short term I could use the emonTx to capture gen data before I had a chance to work out how to import the SE data via code.

Thankfully my Immersun is still working at the moment, so will wait until the liquidation has been completed before making any longer term decisions on a diverter replacement.

Hi Matt,

Yes I have gained access to the data. The SE system only allows installers to gain access to API tokens, so I suggest you speak with them. I have seen reports that SE (direct) have split installations off onto new accounts in the past which allows end users to gain access to the tokens when installers have been unable to.

Does anyone know of any working code to import Solar Edge data which runs on the emonPi?


Interesting. I’ll contact my installer first then. Currently I have a hokey script that uses the APIs that their website uses to get data.

I imagine this will be simple with the data. I’m happy to work on this once I have the data myself.

Have you considered the smart plug route like I’m going with?

I am happy to work with you on this if it would help. I am a software engineer by trade, just not one in the languages of emonPi.

The Immersun is hard wired into the dis board due to its current draw requirements rather than a plug/socket solution, so that is not an option for me.


Hmm now you’ve made me wonder. I don’t think I should be doing what I’m doing. My PV is 2.56kWp so max I’ll ever really divert to immersion is 2.4kW likely. So the plug should be able to handle that. But it’s worrying me a bit.

I’m getting a spark in to change our fuse box soon (it’s an old one!) so I might get him to sort this out while we’re at it, and leave me some space to have a CT on the immersion circuit.

Matt, yes my situation is a little different in that I have a 4kW PV so it can in theory at least saturate the 3kW immersion element. This is getting very close to the limits of a 13A plug.


I’m so jealous. My dad has 3.75kWp. We could only fit on 8 panels, just. Went for 320W panels to give us 2.56kWp. To be honest, I’m really happy with it. But it does pain me that even in peak production, I can’t power my kettle for a brew!

A standard BS1361 13 A plug and socket in good condition should be good to, erm, 13 A. That’s over 3 kW by my reckoning if everything is purely resistive, or possibly just under 3 kW given that the mains is normally inductive with a p.f. a bit less than 1.

But what would worry me is the possibility, however slight, that the inverter could continue to generate even for an instant as the plug was withdrawn, leaving live pins readily accessible. Your inverter really must be permanently wired in.

Have you ever looked at the characteristics of a BS1362 cartridge fuse? There’s a Building Blocks piece about protection. I think you should read it.

UL 1741 and IEEE 1547 specify a max of 20ms 2 seconds from loss of grid voltage to inverter shutdown for grid interactive inverters. So the plug could indeed be live after disconnect.

I would hope that " loss of grid voltage" would be detected within 10 ms, but that could extend the period to 30 ms. It’s highly unlikely that anyone could make contact with the pins that quickly after the circuit was interrupted, but that’s always assuming that the inverter operates correctly.
[Edit] In view to @Bill.Thomson’s correction, this becomes totally irrelevant. See my post below.


Major correction to my earlier post. The UL spec is 2 seconds. (post corrected)

It’s my Enphase micro-inverters that are spec’d at a max shutdown time of 20ms.

To comply with IEEE1547 the interconnection system must:
* Exhibit a fixed 5‐minute time delay or adjustable delay of 5 minutes or less on startup/restart
* Respond to abnormal system conditions (voltage/frequencyexcursions) per IEEE1547.
* Not exceed steady‐state harmonic and DC current content limits.
* Not produce objectionable flicker.
* Detect and cease energization of the grid during unintentional islanding within 2 seconds.
* Pass synchronization and interconnect integrity testing (EMI and surge withstand).


In that case, there’s a very clear danger should the inverter be unplugged. @mattjgalloway
you really MUST get rid of the plug and socket and make a permanent connection.

It’s your and your family’s safety versus the convenience of a measurement. That’s no contest in my book.

The inverter isn’t on a plug, it’s the immersion. Sorry, I’m confused! I follow what you’re all saying, just, but I think I’m missing something.

Now you got us all confused! (Actually, I think it was Ian who suggested the inverter was on a plug and socket.)

OK, so the inverter is indeed hard wired into your consumer unit presumably, or into Henley Blocks. That’s a relief.
I wouldn’t worry too much about an immersion heater on a 13 A plug, provided both plug and socket are in good condition - unplug it once in a while just to keep the contact surfaces clean, and check that it remains cool in use.

So yes, if someone is using an emonPi with 2 current inputs, that will give you nett grid power and PV generation, from which you can deduce house consumption including any diverted power, and a separate monitor on the immersion heater feed will give diverted power alone.
Alternatively, if a measure of PV generated power is available from the inverter, then the emonPi can measure nett grid and diverted power, import generated power, and from that you can again deduce house consumption with or without diverted power.

Nope was not me, I think you must have misread the thread.

So thanks for confirming what Matt and I suggested at the start of the thread. Much appreciated.

So I have my Solar Edge API key, but it doesn’t seem to be working!

@lake - are you hitting something like this?:{siteid}/details.json?api_key={apikey}

I’m thinking they’ve generated me an account users key instead of a site key, possibly, which I’ve now asked them. But just wanted to check I’m using the API correctly. I mean, this is my bread & butter (also a software developer by trade!) but it’s entirely possible I’m just being stupid!