Help with getting started with Solar PV and battery

I bought a EmonPi back in 2017 with one CT clamp and used it to monitor household usage. When we moved I never reconnected it (cables by the meter were a pain to get to and no power for the EmonPi), so it’s been gathering dust ever since. I’ve now had Solar PV (Solis) and battery (Pylontech) installed and wanted to get the EMonPi running again as the available stats are poor in the Solis portal.

I was wondering what I need to get, I assume another CT clamp for the current EmonPi and connect as per the type 2 example in the SolarPV docs and connect these by the meter.

The inverter and battery are a long way from the meter so what should I do about battery monitoring and is there any addition monitoring I can do at the inverter end? Looking at the portal at the moment what I am missing is when is the battery charging/discharging I’m assuming there is nothing I can do see the charge % of the battery except on the portal. The other thing is I have panels on 2 aspects and would be interested in seeing the power generation of each but as this is DC I assume this isn’t possible. The portal is showing 227V at 6.6A on one array and 139V 0.7A on the other and that is interesting to see that balance and if the second array was worth installing.

So what hardware/software do I need to achieve this? I’ve upgraded the old EmonPi, I assume the HW is good enough even being 3 year old?

Welcome, Chris, to the OEM forum.

First, your old Pi should be fine, if a bit slow.

I take it you have only one inverter and one a.c. infeed from it? Does it have any means of communicating with the outside world, other than the front panel display? If it has, and the protocol is known, available and it’s not encrypted, then it might be possible to extract the data and use it.
Roughly the same applies to the battery’s inverter.

I would definitely advise against messing with that. Get on the wrong end of that and the consequences could be very serious.

A lot depends on how and where these items are in relation to your meter. It looks as if you’re going to need one, maybe two emonTx’s as well as your emonPi - depending on how everything is connected physically as much as anything. You’re obviously thinking that the emonPi needs to be at your meter/incomer, but that’s not necessarily the case. Whatever you do put to monitor the grid connection, you’re going to need a voltage there to give the direction of power flow, hence at least one, preferably a double, mains socket.

My outline thinking is:

  1. At the incomer, an emonSomething measuring the grid power and direction.
  2. At the PV inverter, an emonSomething measuring the PV infeed power.
  3. At the battery inverter, an emonSomething measuring the battery power and direction.

It depends on how your wiring is configured, as to which of these can be combined and done together.
One will be your emonPi, which will collect all the data. Whether that can be by 433 MHz ISM band radio (built in to both the emonPi and emonTx), or whether it needs to be wired Ethernet or Wi-Fi, depends on far “a long way” is and what’s in between.

Thanks for the reply Robert.
Yes, one inverter with one AC feed from it. Yes the Solis has the wifi adapter and sends data to the manufacturers portal but you can chose a second destination. Most of the bits I’ve seen on it seems to be vague as the data layout isn’t published so people have reverse engineered the values by looking at the data in the manufacturers portal and the data coming in. That said there seems to be problems with this as the data has changed in the past and no one has a complete list of the data. I will be looking at that but part of what I’d like to do is have at least 2 sources of data to validate them, is the data from the inverter more accurate than the CT clamp or vice versa. The data from the inverter is only sent every 5 mins as well. There is some info on the battery as well even though it is not the same manufacturer so again no idea of the accuracy. The battery has a console port and CAN/RS485 ports I’ve seen people publish some scripts that issue commands and screen scrape the console the port. Again I’d like to look into that as well. The digging out of the emonpi was basically a quick win, buy some bits and clip on the clamps.

For locations etc. the meter is in the back of a kitchen, with the PV fuse board and feed in meter. The inverter and battery are in the loft directly above the meter, so 2 ceilings plus 2 cupboards full of stuff at least between them, but no brick walls. How directional is the 433MHz band as it need to traverse straight along the wall vertically. I’m assuming there won’t be interference from the Zigbee/Zwave/Wifi being on that frequency as I have a bits of that all over the place connected to Hassio. Iwas thinking of adding Lightwave at one time but never managed to get a cheap hub. There is a double socket by the meter and 4 sockets by the inverter so no problem with that.

I was assuming I would measure the grid and inverter at the meter but I guess what you are saying is just measure the grid there with the existing EmonPo and buy a 2 clamp emonTX by the inverter and measure the battery and inverter there? As emonTX wifi adapter is out of stock I guess I can just try it and if it doesn’t work order that later. You mentioned wired but it didn’t look like you could wire the emonTX or is the RJ45 multipurpose? I have a number of Cat6 cables dropping through the loft to the central switches.

You mentioned the old Pi being a bit slow, I was looking around and it looks like you can get docker images to run the software I have a couple of machines running docker so could move that off of the Pi. Is it easy to get the emonPi to send it’s readings to that rather than doing it locally?

I’m running emoncms on a PiZ so it’ll be fine and you will just complicate the setup IMHO.

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So I take it that the battery inverter feeds into your ring main “up there” somewhere, i.e. it doesn’t come down on its own and feed it at the main consumer unit. And that does mean you need to measure the battery power there.

The aerials we use radiate in a doughnut pattern - they do NOT radiate in the direction they point. So point the aerial horizontally and it should be OK. I can’t say if or what interference you’ll get from other devices.

It doesn’t really matter where you measure the PV, whichever is more convenient is the factor - unless there’s something else in the kitchen that you’d like to measure separately.

Yes it is - but that doesn’t include Ethernet. It is solely an input for the pulse and temperature sensors. You’d need a serial to Ethernet adapter. As there’s nothing substantial - like stone walls - in the way, I don’t foresee a problem in using the radio.

I’m only going by what others have reported. I’ve no experience of docker, all I can say is we have a lot of experience with the Pi. You still need the Pi to receive from the emonTx, so depending on how much data processing you do, so although it’s only one line in the configuration to send the data, it might not be worth the trouble of setting up another machine with another copy of emonCMS.

You will see a discrepancy between the c.t. as it comes, and the meter. It depends on the loads you have, but over a period I’ve been able to calibrate an emonPi to better than 0.5%, which isn’t far away from the accuracy of the meter.

If it’s “too hard” to extract the data from the two inverters, you’ll at least be able to tweak the calibration to match the inverters by reading the meters and noting the discrepancy every week or more. How accurate those are, you must check, but you’d very likely need some reasonably high-spec test gear to calibrate your emonTx and emonPi to better their accuracy.

No, the inverter has a cable run down the outside wall and is connected in it’s own fuse board by the consumer unit. So I can read at either point, I guess measuring by the consumer unit would be most accurate although the loss on the drop down will be negligible.

I just realised the battery is DC, so I can’t measure the supply from that in any case. I’ll need to go down one of the other routes to see the battery usage. So extra CT clamp on the existing emonPi and setup as normal for PV.

Erm… Yes. :laughing:
But the inverter output is where you need to be measuring.

You can’t do that, you don’t have a spare input. You have just two on the emonPi - one for the grid and one for the PV or the battery. I suggest you use the emonTx in the kitchen for all three - grid, PV & battery, forget the radio and just use the Pi with a serial connection between it and the emonTx. That would save you on a.c. adapters (one only needed) and negate any worries about interference on the radio.

One inverter with 1 AC output and 2 x DC panel array connection and 1 x DC battery connection, I won’t know if the power from the inverter is coming from the battery or PV panel. So I cannot measure the battery externally only by whatever the inverter is sending through its own built-in monitoring.

Oh I see. You didn’t make it clear that the battery and the PV used the same inverter.
In which case, your best plan will be to try to find out how to extract the data from the inverter. When you can, we can look at how to get that into emonCMS along with the power data that the emonPi measures.

Thanks Robert
I’m new to Solar and been getting up to speed, every day brings a new learning experience. So some things are a surprise to me, as to things that should have been aware of I either spot or get told. One of the things I was doing with this install was trying to learn, as we want to do a new build in the future and for that I’d like to get it perfect. I guess I know the basics… power is being produced and I’m using some and giving lots of it away to the grid until I can get a smart meter, which seems impossible to do at the moment.