Thanks to all those who have responded to my initial post: I understand much better now what can be achieved, and I’ll shortly be in a position to make an order. I’ve run what I’ve learnt by the Italian electrician who originally did the PV installation ten years ago (so he knows where the bodies are buried), and he is actually keen for me to make an order so that he can do the electrical part of the installation, because he likes the look of such a non-invasive solution, which he could propose to other clients – the hardware he’s used until now involves running extra new cables to the PV inverter. The emonPi/Linux configuration part will be down to me (I’m not sure how much of that he’d be au fait with), but I’m on much safer ground myself there. If he’s keen for me to proceed, then I’m keen to try and make what he’d need to do in the future for any other clients as simple and ‘standard’ as possible, and I’d offer to informally ‘consult’ if appropriate, based on my experience of my own future installation.
My house and PV system are three-phase, though. From the responses to the thread, it seems like I might have two main options, with pros and cons for each. I’d be grateful for any comments (or corrections) on my analysis of my best options below:
The full emonPi PV monitoring package, which comes with two CT sensors, for one phase, plus two emonTX units, with four more CT sensors, for the other two phases. This is based on what garnhedryn (Brian Davis) contributed. Four new power sockets would need to be installed, at least one per phase, with the emonPi requiring two sockets.
An emonBase, with three emonTX units, and six CT sensors, two per unit. This is based on what gadgetbazza (Barry Tresadern) contributed. Three new power sockets would be needed, one per phase (if the emonBase were installed a few metres away in the house).
The photo below shows where one of these installation options would go, following confirmation by the Italian electrician. This is a corner of my property, a covered entrance area with the road (and electricity meter) on the other side of the wall on the left, and a neighbour’s property behind the wall on the right. This is where the electricity supply from the grid enters my property (the cables run above ground between concrete poles, along the road, and a line comes down to the meter). This covered entrance is effectively a room, open to the elements at one end, where a set of stairs then leads down to the veranda, from where you enter the house (which is set below road level, the property being on a slope). But this is Sicily, so there is no frost risk, and the location, covered but outside of the house itself, should be ok. I imagine the emon kit, and the sockets they were plugged into, would be contained within a suitable box installed on the wall near the two boxes shown.
The top box in the photo is the first entry point from the meter on the road, and has some surge protection. The lower box contains the six cables I would need to put the CT sensors on: those for the three phases coming from the grid, and also those for the three phases coming from the PV system and inverter about 80m away at the bottom of the garden (this now having been confirmed by the electrician). As Robert Wall pointed out, this lower box thus effectively constitutes the ‘Fuse box / consumer unit’ in the ‘Type 2’ diagram at the beginning of the Solar PV section of the guide. Presumably from here, cables are ducted into the house, initially to the board of circuit breakers, and this is the decision point where energy generated by my PV system is either diverted into the house for consumption, or exported to the grid (with the meter on the road functioning as an export meter, as well as recording consumption).
So the emon installation would go here. To look at the pros and cons of the alternatives:
- emonPi and two emonTX units.
Three units, rather than four in the alternative – but the cost is probably similar for either. The emonPi would need to be installed here on the wall (and not in the house), but the electrician says he would duct an ethernet cable from there through the house to my internet router (although I have experimented with a wifi extender to this point, which seemed to work ok). The emonPi and the two emonTX units are next to each other for radio traffic, and the danger of radio collisions is presumably reduced by having only two emonTX units rather than three. The emonPi can only have two CT sensors (which is all that I need), but there is no expansion built in, as there would be with three emonTX units (each of which can have four CT sensors). If I understand correctly, I would be able to keep the standard sketch with this configuration, whereas I would need to intervene to switch to the three-phase sketch with the three-emonTX alternative. Similarly, I can order the two emonTX units to be configured with two node IDs at time of purchase (set by a dip switch), whereas if I order three, then I have to invoke a procedure myself to reconfigure one of them to a third node ID. These last two points have to do with the ‘out-of-the-box’/’keep it simple’ idea I mentioned earlier.
If instead I go with a three-emonTX solution, then I have available four CT sensors per phase, and I can keep the emonBase inside the house if I wanted (about 12m away from the wall location, with line-of-sight through a wooden door). I imagine the location of the emonPi/emonBase inside or outside of the house is probably not too important, as long as it can communicate easily with the internet router, and I would in any case be viewing the emonCMS data on another computer via something like VNC.
However, I am concerned by the potential radio clashes between the three emonTX units and the emonBase that others have written of. I would prefer to stick with the default radio solution if possible, in part because it’s more ‘out-of-the-box’, but also because alternatives (such as the ESP8266 wifi module) involve more power consumption, meaning the AC-AC adaptor for each emonTX to measure voltage for that phase can’t also handle this extra power requirement, and the 5V USB power supply must be used too, doubling up on the power sockets I would need to have installed. So, to keep it simple, I’d ideally like to use the default radio option. However, I’m making the assumption that two emonTX units communicating with an adjacent emonPi via radio does not involve much of a risk of collisions, whereas three emonTX units communicating via radio with an emonBase maybe a few metres away may instead be problematic, as it evidently has been for some people. Is that a reasonable assumption?
Based on the above considerations, I’m currently leaning more to the ‘emonPi + 2 x emonTX’ option rather than the ‘emonBase + 3 x emonTX’ alternative, because of the reduced risk of radio collisions and because I might need to intervene less on the ‘out-of-the-box’ configurations (no need to intervene to change sketch, or change node ID).
I’d be grateful for any comments, advice, or corrections to my reasoning as expressed above. I’m ready to order, and keen to get started, but don’t want to have made any show-stopping mistakes – my background is not technical.
The last thing that is worrying me is Italian customs, post-Brexit. I recently turned 70, and arranged online to have my new driving licence delivered to my UK address, intending to pick it up during a (subsequently cancelled) Christmas visit. My brother picked it up and sent it on to me, inside an apparently oversized birthday card for me, using Post Office Track-and-Trace. This shows it entered Italian customs on 24th January – and there’s been no change to its status since then. From what I can make out, using Track-and-Trace designates what’s being sent as a parcel, which now means it has to go through customs. If a birthday card can get lost in Italian customs for nearly three weeks, what’s likely to happen to the hardware for a (small) energy monitoring solution?
The Shelly 3EM suggested by Zoltan would not have this issue (Shelly apparently distributes in Italy), and is intended for three-phase, but this certainly doesn’t look ‘out-of-the-box’, I can see it isn’t ‘open’, and I would need too much support in things I don’t know about. I need to learn to walk before I can try to run. Regarding Italian customs, I can but hope… my now-belated birthday card (and driving licence) would be a start.