What do I need as a real newbie?

Just discovered Open Energy and I’m interested in setting up a system to monitor my solar PV system.

Unfortunately it’s installed on my garage which is too far away from my router to connect via WiFi and hasn’t an ethernet connection so it looks as if I can’t use the emonPi unit. It looks as if I could use an emonTx plus a emonBase if the wireless signal will reach it (I have a wireless bird box camera on the garage which works OK) to upload data to emoncms to be able to remotely monitor it. What I need to know is - can I just buy these units and “plug and play” and start using them without any programming? I have no experience with programming languages so I would be reluctant to do anything in this area!

As I see it I would need at least:
emonTx + sensors & power adapters
emonBase + SD card image + power adapter

Am I correct?

Sorry to appear thick but I don’t want to splash out on kit which I’m unable to configure!

Why can’t you use the emonpi for it?
you can still log locally and spawn a wifi network from the raspberry pi 3 directly. However you still won’t have webaccess… that’s true…

OR you could use a USB Mobile network modem to upload your data to the web (this woudl require an internet plan with a sim, in germany you can get 100 mb free at netzclub …)

but in principle you can also use an emon tx and the emon base, but I don’t know if there is absolutely no programming to do… To my mind you need to at least install the emon base, this needs some configuration work, however no real coding. just reading, understanding and changing some values in text files on a linux shell. Nothing toooo fancy, but if you are a total novice with linux shell it’ll take you a few evenings.


If you think you need to write code, not really needed. You can if you want to customize since it is open source. But you can just do basic install and use some basic pre configured tools to monitor a solar production site.

Have you read this ?

and this ?

You should be able to plug&play, but the accuracy won’t necessarily be perfect. You can do tweaks in your web browser to correct that to a large extent, though.

What is the distance, and how many walls (and what construction) are they? And what radio frequency does your camera use? That could be a worry.
If you’re sure WiFi won’t reach, then your list looks OK. If you want accurate real power, you’ll want a CT and a.c. adapter for your emonTx. You’ll need a 5 V USB power supply for your emonBase. You can download the image, or buy an SD card with it loaded. You can log in to the emonCMS on your base, and/or you can send the data to emoncms.org.

Where does your electricity come in, into the house or the garage? Is there anything in the garage that uses significant power?

Thanks Robert (and all other responders)

The distance is about 30m and the walls are 15 inch solid brickwork (the house is 140 years old) but there are windows facing the garage where I could put the receiver. Nothing in the garage uses significant power - basically only the webcam and some weather station sensors.
When the garage was built a new supply was taken from the house incoming supply and connects through a separate consumer unit connected to incoming supply before the main existing consumer unit. I.e. the incoming supply splits through a junction box - one to the old consumer unit and one to the new (garage) one.
Now I’ve looked at it I realise that I can see the two tails from the incoming supply in the house going to the garage consumer unit so maybe I could clamp the CT sensor onto one of these? I suppose the power measured here would be the output of the solar PV less any power taken by anything in the garage?

That was my hope when I asked the question! So yes, measuring there will indeed give you your PV output, less the power consumed in the garage. Camera & weather station are probably in the order of a few watts, but not forgetting the occasional battery charger & vacuum. You won’t have all that much error by ignoring those.

So it’s looking more like an emonPi - one CT on the garage feed and one on the house feed. You’ll need two CTs for that, an a.c. adapter if you want decent accuracy, and a 5 V USB adapter to power it. It’s got WiFi, so as long as it’s in range of your router, you should be in business.

Thanks Robert, it’s really close to my router so I’ll go for it & let you know how I get on!

Ordered yesterday and arrived today - fantastic service!

Set up with no problems - now (i.e. night time) solar is showing 17W which must be my camera and weather station so not enough to worry about.

Couple of small issues though:

  1. On my Android app I can get ‘Power Now’ reading OK by nothing under ‘Use Today’ and no bar graph. On settings, bar graph feed shows House Power kWh and selected. House Power kWh shows up OK on emoncms.org/feeds and local (

  2. Vrms shows 265.6V but measured with a multimeter the voltage is 245. AC. I have the AC power adapter connected and recognised on boot up

Any help/advice would be appreciated!

I can’t tell you about Android - someone else will need to answer that.

The calibration is a long way out - around 8%. Are you sure your multimeter is accurate?
However, you can change the scaling factor of all the inputs by editing the file emonhub.conf. You can do that via your web browser. For Node 5 (the emonPi itself), the number in the line “scales = …” correspond 1 : 1 with the inputs listed above. You’ll need to change the 0.01 for the voltage (it is sent as an integer value, e.g. 26560) to something like 0.00926. The two powers are calculated using the incorrect voltage, so those will need to be calibrated too.

Thanks Robert - I’ll have a go at recalibrating tomorrow (!later today!). I’ve no reason to doubt the multimeter as I can’t believe my mains voltage is 265 but I will borrow another one to check it.

Re the Android app I checked it again after midnight & it’s now showing a bar and reading so I assume it doesn’t register for the first day.

I didn’t believe your 265 V either, as it should be no greater than 254 V but if you have an unnecessary power factor correction capacitor nearby - that could have pushed the voltage up. If all the tolerances went the wrong way, you could have been reading about 257 V instead of 245, so something is out of specification.

The voltage calibration depends on 3 things, the voltage ratio of the a.c. adapter, the ratio of a pair of resistors and the actual value of the 3.3 V d.c. supply to the Atmel328P inside your emonPi. If you feel like taking your emonPi apart, you could check that (3.3 V & GND are the two end pins in the row of 3 on the edge away from the input sockets on the 6-pin header on that smaller pcb), and you could check the a.c. adapter - it should read 11.6 V ±3% at 240 V in. If those two things are right, it has to be the resistors, and whichever, we’ll take it up with G&T.

Thanks again. Not sure about a power fraction capacitor – would I have one in a domestic installation?

I’ve measured the voltage from the ac adapter & it’s 11.2V which is just about in the 11.6 V ±3% range.

Re measuring the 3.3v dc I’m struggling to find where the 3.3V & GND pins are – I’ve attached two photos of the main circuit board – could you point out where they are?



Any luck with the Android app? It takes over 24 hrs to generate an energy used bar graph. Could you post a screen grab to illustrate the problem and your settings (emoncms feeds, and android app settings)

Thanks Glyn

Yes, I discovered that it takes time to generate a bar graph - when I checked it at just after midnight a bar had appeared and it’s showing the correct figure now (12 noon).

Really impressed with the support on this forum - I only connected my EmonPi yesterday evening & needed some guidance & I’ve had so much help from people, especially Robert. Thank you all


“Factor”, not fraction. There are companies that sell these with a claim that improving your power factor will somehow reduce your bill. But as you pay for power, not VA, it’s hard to see how that claim can hold up. So unlikely that you have one, but if there’s a neighbour on the same phase, or a small industrial unit on the same distribution transformer, it was a possibility.

Oops! Yes, I know it should be power factor - a slip of the fingers (not as young as they used to be!). That’ll teach me to read through posts before hitting send.

Voltage = 3.3 so that’s correct…

There is a farm with a 3 phase supply coming off the same distribution transformer across the fields with various bits of kit like a grain dryer so it may be that. On our phase there’s only us and next door which is also a private residence.

Anyway I’ve recalibrated using a factor of 91% for voltage & power & it now agrees with the voltmeter so I’m happy!

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