PV production monitoring

[sam]

I'm expecting to get PV installed shortly and wanted advice on anything sensible to install at the same time to assist with production monitoring.

 

I'd like to be able to monitor the PV production and export in order to maximise my usage. I know that there are commercial systems to control immersion heaters but more likely I'd build something using Arduino (or something similar) like I think @ProDave  and @JSHarris have mentioned they have done. At this stage I'm asking if there is anything I should consider installing near the inverter or meter to be able to capture the necessary data. I know I could get a clip on power meter which could easily be retro fitted but I was wondering if some kind of meter was more useful or easier to export the data from in an accessible form. 

 

I currently have a digital E7 non-smart meter and expect to have a Solis inverter. I know that Solis sell a wifi or ethernet adapter but I'm not sure if the data from this is accessible.

[ragg987]

I have a solaredge inverter, monitoring is standard via an app. You need an ethernet cable.

[sam]

Thanks @ragg987; what I'm hoping to do is be able to access the data to program other devices, rather than just view it. Do you know if that is possible with the solaredge setup?

[Jeremy Harris]

I built my excess PV diverter using an electricity meter chip to measure true power accurately, sensing the supply voltage and phase via the power supply transformer for the unit and sensing current magnitude and phase via a clip-on current transformer.  It's been working well for a few years now, and is documented here:  https://picaxeforum.co.uk/threads/photo-voltaic-immersion-heater-power-diverter-safety-warning.24286/

 

I've since altered this slightly, by adding an 868 MHz wireless link, so that instead of directly switching a solid state relay this unit has been rehoused in an IP65 case and outputs serial data via the wireless link to a second switch unit inside the house, which turns the SSR on and off to control power to our water heating system.

 

This unit now also broadcasts power consumption every ten seconds over a second 433 MHz wireless link, which enables stuff in the house to either display data or use it for any purpose (I'm currently sitting writing some code for an intelligent car charge unit, so that I can charge my car at a variable rate depending on excess PV generation).

[ragg987]

I think they publish an API (I have a vague memory of registering this to use a third party app).

 

I also use an immersun with the add-on monitoring myimmersun device connected via ethernet cable. This can provide 5 measures (generated, imported, exported, diverted, consumed) and uses current clamps. You can log into their website and download the stats since year dot, though these are aggregated to 1hr. If you Google, it seems someone has reverse engineered the app and was able to write their own script to intercept the measurements. Went over my head.

[ProDave]

Yes my own is based on an Arduino.  I am on the process or re vamping it to make it operate somewhat different to it's previous incarnation but am held up for a second current transformer, somewhere between China and the UK at the moment.

 

I could do a write up when it is done as long as you all promise not to criticise my sloppy coding.

 

As well as sending excess power to the immersion heater, it will have a simple (old fashioned) moving pointer meter to show import or export (half scale = 0, left of that importing, right of that, exporting) and will log the number of watt hours of power sent to the immersion heater.

 

I also have it in mind that at some future date it could be expanding to control charge and discharge of a DIY battery storage system as one integrated system.

 

[sam]

Thanks for the useful replies. At this stage I'm wondering if there is anything which is sensible to install at the same time as the panels and inverter.

 

Can you recommend the meter chip?

 

I'll read up on your code but at the moment my actual coding and immersion/heat pump controller side of things can come later!

 

 

[ProDave]

Unless you go for a wireless solution, you will need to decide where the immersion controller is going and then get a current measurement (probably from the consumer unit) to that point.

 

In my case the incoming supply and thus easiest place to measure is out in the meter box.  But I predicted that situation and I ran a spare length of 5 pair armoured telephone cable back to my comms / AV cupboard, and from there a CAT5 up to my plant room.  That gives me 4 twisted pairs from the meter box to the plant room for my current transformers and a couple of spares.  The one I already have connected seems to be working okay.

 

The electricity meter chip is probably a better idea, that can still be hooked up to an arduino if that is what you are familiar with programming.

[Jeremy Harris]

The chip I used seems to be obsolete now, and finding a DIP version of a similar chip may not be easy (I've not looked for a few years now), but there may be some around.  Pretty much all the electricity meter chips work in much the same way, and have similar interfaces, so it shouldn't be too hard to find one.  An alternative might be to get an additional meter installed.  The Elster A100C is a really good option (around £30) as it has an optical serial data port, that constantly outputs power, current, voltage etc.  The data protocol is documented, so it's relatively easy to just stick an IR receiver on the meter port and get all the data you need.  This link has details about doing this: http://openenergymonitor.blogspot.com/2012/08/reading-watt-hour-data-from-elster.html

 

This link has a bit more on the protocol used: http://abatis.org.uk/projects/rdmeter.html

 

Edited to add:

 

I found the A100C datasheet, which has full details of the data transmitted etc: A100C_Operating_Instructions.pdf

Edited February 22, 2019 by JSHarris
Added info

[sam]

Thanks again for the useful posts.

 

Where in the system is the official meter used for FIT and Export payments? Is it possible to use this data or is it not in a useful format or sufficiently real time for this?

 

The Ginlong Solis inverter (and many others I believe) has a RS485 interface and a 'COM' interface. A wifi (or ethernet or GPRS) connector can be purchased. Does anyone have experience using this to get production data or again is this not in useful?

 

[Jeremy Harris]

You can get generation data from the inverter, but if you want to control something like a immersion heater you need net export data from the incoming supply cable, hence the reason for either using a current transformer around one of the meter tails or taking the data from an extra meter fitted in line.  Getting data from the suppliers meter is possible, but usually only to a resolution of about 1 Wh from the flashing LED, as meters like the Elster A100C, with it's handy data output, don't seem to be in common use by suppliers.

[ProDave]

Various inverters have some form of data logging built in. At my last house we had a Sunny Boy inverter, but on spite of trying 2 laptops, and 2 different bluetooth adaptors on a desktop pc, I could never get the bluetooth connection to connect for more than a second or 2 at a time, so I gave up trying.

 

The generation meter goes between the inverter and the consumer unit. That is the oficcial measure of what you generate, but the inverter will also record that.