System with PV on outbuilding

I’ve skimmed through the documentation, but I’m not clear as to what I would need to monitor my setup.

I have approx. 3Kw of PV mounted on the roof of my workshop at the bottom of my garden, some 100 foot from the house. The inverter feeds into the workshop consumer unit, which is fed from the house consumer unit via an underground cable.

I’d have to monitor PV input, workshop loads and house loads.

I take it that rather than the nett power flow to your workshop, you want separately at the workshop the PV generated and the workshop load, and at the house the house load?

I think you need an emonPi in the house monitoring the nett grid power and possibly the nett workshop power, and an emonTx in the workshop monitoring the PV infeed and the workshop consumption. If the emonPi and the emonTx have a reasonably unobstructed view of each other (not thick stone walls), then you will be able to send by radio the emonTx readings, and combine those in emonCMS running on the emonPi with the emonPi’s own readings in the house. The house load will be the nett grid power plus the infeed from the workshop. As all these quantities will be signed, that will give you what you ask for.

So you need:
1 - emonPi and SD card
2 - ac adapter
4 - 100 A CT
1 - 5 V d.c. power supply for the emonPi

If you have very light loads (compared to 100 A), then you might want to consider a smaller CT than our standard “shop” one.

WiFi or cordless phone signal to the workshop is marginal. That’s kind of where I was getting lost, looking for a wired solution.

There an unused Cat5E and possibly a spare 8 core alarm cable running down to the workshop.

We use 433 MHz, a much lower frequency than WiFi or mobile phone. What is there between where you’d put your emonTx in the workshop and the emonPi in the house? (Walls, foil moisture barriers, vegetation, other buildings, etc?)

You can do serial with the emonTx, it’s just not our standard offering (and I’m not certain that 100’ would be do-able without going to RS422 and the added complication of drivers and receivers). This is in fact how the cut-down emonTx inside the emonPi communicates, but the distance is quite a bit smaller! Having written that, I’m not certain that you can do a second serial input to an emonPi - @glyn.hudson or @pb66 can probably help here.

If you replaced the workshop emonTx with a second emonPi, that could plug in to your LAN and be accessible that way, but then I think I’m right in saying that you’d need to do a lot of work in software to integrate the readings.

As the workshop has a power connection to the house is Ethernet over power (Powerline) not possible? I have normally good results with them on the farm of my father-in-law. He has a 6kw PV install on the horse barn.

Correct, RS422 requires a driver chip. Neitther the emonPi or emonTx supports RS422 without extra hardware.

A USB to UART programmer could be connected to the emonPi to create another serial port

Powerline Ethernet is probably the easiest option, but maybe not the cheapest.

And I, or more accurately a friend living in rural Scotland, had his Ethernet over Power converters blown up by the spike from his neighbour’s milking machine. I ran cables for him instead.

Might as well use a USB to RS422/485 converter: Powered by the USB port, no drivers required.
One on each end would do the trick. Inexpensive too. This example is 9.96 USD:

Just a bit more than 2 USD if you get it from fleabay.

From a UK seller on Fleabay, it’s 3 quid, free P&P.

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You could use a USB over Ethernet and connect the remote emonTx to the emonPi that way, but for the same or probably less money, you can set up a second Pi with a serial-direct connected emonTx and gain the extra IO for if/when you want to expand into more monitoring or control.

A Pi B or even a Pi Zero with a micro-usb Ethernet adapter would do it for even less outlay.

[EDIT - if you do use a Pi you could also set up a wifi AP so that you have workshop WifFi too]

Thanks for the responses. I went ahead and purchased an emonpi + emontx, we’ll see how well the wireless signal works. I can probably mount the tx on the other side of a brick wall if the signal is marginal.

If the wireless is a no-go, then going to RS422/485 isn’t a problem. I probably have a couple of TTL to differential driver chips hanging around.

And if you don’t want to / cannot mount the emonTx on the outside, then you ought to be able to extend the antenna with a suitable SMA cable and have just that outside.