What components do I need to measure my solar power and import export status

Getting Started
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Hi although an electrical engineer am new to this system. So I would love some advice.

I have a small 640w solar system in my garage on a sub consumer unit to the house. The aim to remove my base load. So my mains incoming cables are not collocated with my solar cables. This would mean that my CTs would be in separate places in the house.

What equipment would I need to buy to display my solar and mains import or export.

I have a supplementary question. I at present have an efergy clamp monitor. But put simply it can’t cope with true power, I don’t know if it’s harmonics or power factor but I can get strange results if I try to increase my load sometimes input power is even going the wrong way. Doing a quick check on led pulses shows the power to be often over reading. Does this system measure true power or va.

As I say I have a good understanding of mains and electronics but all these products are new to me so some advice on what I need to build a system would be great many thanks.

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Welcome, @Whitehse46 to the OEM forum.

Let’s deal with the Efergy kit first. I don’t know which particular model you have, but most of the commercial monitors fall down in several areas. If the c.t. is linked by radio, then it almost certainly reads apparent power, and if the base unit/display is battery-powered, it almost certainly uses a nominal or your ‘best guess’ at line voltage. So it could - and some makes do - have both those failings, and a ‘best guess at v.a.’ is touted as power.

As regards replacing it with OEM kit, we’ve just received a first shipment of the new emonTx V4, how many are spoken for and how many are sold I don’t know. As far as I know, the old emonTx V3 is out of stock. I see the combined base unit/monitor, the emonPi, is also out of stock at present.

So what would you want if The Shop could supply it? Is it possible to run a ‘microphone’-type cable (or Ethernet Cat-anything UTP or FTP) between your C.U. and the garage? If it is, and the distance isn’t too great, you could have an emonPi by the main house C.U. and a c.t. on the end of the cable measuring the P.V. infeed.

If your P.V. generation meter has a pulse LED, you might consider an optical pulse sensor on the meter, feeding a pulse count down the cable to the emonPi by the C.U., the emonPi having one c.t. on the mains incomer. The problem with a pulse count is it’s historical, you only know consumption (total energy) at the time of the last pulse. But it’s 100% accurate for energy. It’s not good at all for instantaneous power.

If you can’t run a cable, you must look to radio. If a pulse count is good enough, you can use the optical pulse sensor feeding an emonTH (also out of stock), which sends the count via 433 MHz ISM band radio to the emonPi. If you want instantaneous power as well as energy, then you’ll need an emonTx V4 with the emonVS voltage monitor/power supply (or if one comes up for sale, an emonTx V3 with a.c. adapter and 5 V d.c. PSU) and one c.t. also feeding the data on the same radio channel to the emonPi.

And if you have WiFi in the garage, it’s possible to send the data from an emonTx that way too, by adding a Pi ZeroW or ESP8266 to the emonTx.

In each case, the emonPi needs a 5 V. d.c. PSU and an a.c. adapter, as well as the things I mentioned.

Hopefully an obvious point - you can’t use the LED on your main meter - it doesn’t flash for export, or doesn’t distinguish from import if it does.

If you’re totally confused, I understand completely, so don’t hesitate to come back with more questions or if you need clarification.

3

Ok a lot of stuff in your reply so I might respond in bite size.

All the stuff about real active power all understood. That’s what caused me to discover your site in the first place. As an engineer using clamp amp meter I was starting to pull my hair out in diagnosing some of the readings I was seeing on my solar my house meter and my Efergy (which is as you say a VA device. ) Basically my solar wasn’t being counted and my day total on the Efergy incorrect compared to my house meter.

My garage to my home Consumer unit is about 75 foot etc are you saying I can extend my CT cable to that sort of length if screened etc ie a good bit of CAT 5. If so I could do that as Wi-Fi in the garage is a bit flaky.

I also understand all you say about meter pulses as I’ve been doing some counting, and never considered that option for extending etc.

Now all the PI stuff is totally new to me although am about to try a bit of programming on a small kit to get going.

Ok so there obviously is a equipment availability issue on a lot of components.

Now the bit I also remain thick on is how I see this data. Obviously I have A PC on the home network but do I need a data collection device and a display type device etc to get at this data. This is the area I am most confused in at present

4

I personally only run about half that length, but the c.t. for the V3 is a current source working into a 22 Ω burden, the c.t. for the emonTx V4 is 0.333 V output but similarly low impedance, so if the cable run is easy it’s worth a try. And if not, you could extend it to your router and have wired Ethernet there. :grinning:

The emonPi is, amongst other things, a web server. It hosts a website “emoncms” on your LAN, on which you have pages to see the Inputs (the raw data), Feeds (the data going into an on-board database), and probably the most useful, Graphs for looking at historical data and Dashboards or the MySolar App for looking at live data or pretty much anything. So you access that via your computer, tablet or phone.

1 Like
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So sounds like I need to order an emonPi Energy Monitor - Solar PV Bundle and extend the cable. And see if that works.

As a thought could I extend both CTs and reduce cable length to less by by putting Emon pi at my pc. Does mains sensing need to be at the CU or could it just be on my ring main

Thanks for your help looked at a few you tube things and I’m sort of getting there. I will submit a interest request to the shop and watch the space.

In fullness of time I will be all over this just getting my head round the IT bits of it obviously a lot of jargon used by those in the know. Thanks you’ve been great

6

It doesn’t want to be on a heavily loaded circuit, one that experiences a significant volt drop - for obvious reasons. For example, your PV power will be that delivered to the house, not that coming out of the inverter, because of the volt drop of the cable from the garage. But if you’re using more than you’re generating in the garage, it will read high!

As you are in the UK, I have assumed you have a single phase supply.

:+1:
If you click on my icon, you’ll see we’re kindred spirits. And I’m a lapsed PPL too. My colleague Bill Thomson was in your line in the USA.