Lots of Questions

A little over 6 weeks ago we had 3.77Kw 13 array installation on our garage and shed roof. We are over the moon with the install. The panels feed a solar edge inverter which gives us live(ish) data on our iPhones. 


As as good as this is it doesn't give us exactly what I want in terms of energy monitoring and utilisation of excess generated power. 


I was initially looking at a solar iboost to divert the excess power to heat our unvented tank. I have heard mixed reviews of them and after lots of googling came across this site which I have been actively reading on and off for the last week. 


I'm a software engineer by trade and very familiar with the ardunio Ide having used it myself for a few projects.


As a complete system I am looking for live data monitoring of the PV install and grid usage. As previously stated the install is on the garage / inverter in the garage.


id rather not guess at the modules I need to buy as cost is obviously always a consideration. Obviously I will need to monitor the supply into the house. Does this need to be at feed ie by meter as this would mean I would not have an ac supply (outside electric box). 

Monitoring the solar PV generated via a ct sensor gives me the problem that the invertor would be remote compared to the mains feed. Has anyone had any success grabbing the solar edge data? 


Trying to get a good understanding of how the modules plug together then on to how to integrate the emonglcd. (Looks awesome) and then onto the diverter for the immersion. 

Think thats it for now, thanks



Robert Wall's picture

Re: Lots of Questions

I'm having a problem understanding exactly the distances involved, and where your grid connection is in relation to the PV infeed. Could we have a single line diagram with some distances marked on it, please?

And which country are you in, so that we know what your supply is likely to be?

We have two diverter designs, one by MartinR (Martin Roberts) and one by calypso_rae (Robin Emley). Martin's was designed for the early emonTx but the design has been updated by others since, I believe Robin is currently seeking formal certification for his as a built unit, all details are on his website (http://www.Mk2PVRouter.co.uk). Both offer monitoring facilities, and both are written up here in Resources > Energy Diversion. Both are for single-phase systems.

pgrayem's picture

Re: Lots of Questions

Hi Robert. Thanks for the reply. I'm in uk, north west. I'll get a diagram drawn up tomorrow as off to bed in a moment. The garage supply is fed from the main house consumer unit to on its own consumer unit. The garage is roughly 10m away from the house. Close enough for the solar edge radio comms to work 



pgrayem's picture

Re: Lots of Questions

Picture as per.

I've since found out that the method of comms to upload the PV generation data is a solar edge wireless transmitter (installed in the inverter) and receiver (plugged into my router called zigbee.

Can this transmitted data be captured and utilised as the feed for the pv generation i wonder? or would a CT be more accurate?

Robert Wall's picture

Re: Lots of Questions

That clarifies things enormously.

The questions of practicality:

Can you get a current transformer onto one of the meter tails where it enters your consumer unit?

I assume your inverter back-feeds via the existing power supply to the garage? Would it also be fair to say there's minimal load most of the time in the garage & shed itself, therefore anything you measure coming in at the consumer unit is essentially PV generation?

As you mentioned diverting energy for water heating, where is your immersion heater in relation to the consumer unit. Does it have a dedicated feed or is it on your ring main? Is your bathroom and hot tank above the kitchen?

Knowing the radio comms is zigbee is one thing, but as they supply their own receiver to plug into your router, it's possible - likely even - that they use their own protocol and the data could well be encrypted. You'd need an Arduino and Zigbee shield and then decode/decipher it to use that. I can't remember seeing a report by anyone who's done it. So the certain solution would be to put a CT on the cable to the garage where it leaves the consumer unit. It might be possible to interrogate your data wherever it happens to be, but again I can't remember seeing anything.

If you cannot get at a meter tail, we're sunk for doing the energy diversion the proper and effective way using either Martin's or Robin's design. You also can't get a true measure of the nett energy flow, hence know whether you are a nett consumer or generator. That's pretty important to most people.

If you cannot get at the garage feed, then it is likely you could have an emonTx in the garage, but that adds expense.

Assuming you can have CTs on those two cables, and your immersion heater has a dedicated feed, then one emonTx with a DIY triac switch to control the immersion, and one emonBase, should do everything. Add an emonGLCD if you want present values without going to a web page.

If you need to monitor out in the garage, then you need to add a second emonTx, unless you can extend the CT cable.

If you can't get at the meter tail inside but you can outside, and you can get a thin (3mm diam) cable through into the kitchen and the consumer unit, you can put the CT outside in the meter box and thread the cable (extended if needs be) though the wall and have the electronics inside.

If you want to use emoncms.org for your data, a Raspberry Pi with radio will feed the data into your router (Ethernet or add a WiFi dongle). If you want your data held locally, it will do that too, but many recommend adding a hard disk.

pgrayem's picture

Re: Lots of Questions

Thank you so much for your in depth reply. It will take me a few days especially with it being Christmas to do some investigation as to what I can get to etc. (Not sure the wife would be too happy me delving in behind cupboard on Christmas Day with a torch ha ha ) once I have definitive answers and a plan I'll pop back lay out my proposal if that's ok. Have s great Christmas and cheers

Ps. Direct 2.5mm2 T and E from consumer unit for immersion :)

eskimofisherman's picture

Re: Lots of Questions

I have a solaredge inverter too.  My setup is slightly different as the garage is attached to the house (and the utility meter is also colocated here)

Ive used an emonTx in the garage and installed a CT on the live cable on the inverter output by removing the front cover (6 allen keys).  The output cables are seperated at this point so theres no disruption to existing cables, and there is plenty of room for a CT.    I obviously did this with the inverter isolated. 

Im finding that the emonbase (Pi with RFM69) works well, although its approx 20m away from the garagae and has to go through 3 walls - so you may find that the emonTx can communicate with the house without much issue.  Definitely worth a try. 


Robert Wall's picture

Re: Lots of Questions

Yes, I didn't think 2 brick walls should be a problem, but no cable, even 10 m of microphone cable, would be a much cheaper option if it's practical. Thanks for the input, it's very useful to know that it's easy to fit a CT inside the inverter case.

pgrayem's picture

Re: Lots of Questions

At the moment I'm thinking (without practical investigation at the moment due to Christmas!) is emonPi internal by consumer unit with CT going through wall into outside electric box to cli round incoming mains cable.

Then emonTx in garage to monitor the pv generation side of things. Thanks eskimofisherman for confirmation re the CT in the solaredge inverter housing. 

The main issues I have at the moment (which in the limited time I have to read around places at the moment) is understanding whether the diverter by Robin Emley can send the signal to start/stop consumption remotely via radio comms or the like.

The reason I say this is I've been considering put an electric gel heater in the garage which I would also like to divert to. Obviously these would not be diverting at the same time, but a simple priority algorithm would enable me to prioritize the garage radiator and then the hot tank (or vice versa).

I have also been thinking about the future proofing side of things and thought that integrating the above two into a system along with an electric car charge port would be very useful once we inevitably make that transistion. 

As far as my initial spec / requirements i think I've learnt a lot in the last few days re the separate modules and how they plug together (thanks Robert) and I'm just really looking at future expansion and ensuring it will be possible. The electric heater in the garage would be sooner rather than later as I plan to start on my workshop next summer

Thanks again


Robert Wall's picture

Re: Lots of Questions

You need to read up on Robin's offerings (or make contact via his web site), because he can support dual loads, one via radio (I don't know about 3 though - and if you search here, others have done electric car charging on surplus PV). I was expecting, because Robin's (and Martin's) diverters are fully proportional, i.e. they balance the surplus PV exactly while they are able, that the diverter would be installed next to your consumer unit because it needs the grid CT to measure the nett grid power in order to balance it to zero.

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