Prospective user wanting to monitor PV array, question about Solar bundle

Getting Started
1

I have a rooftop solar PV array that is connected to a sub-panel in my garage. Also connected to the sub-panel is an EV charger. The sub-panel is then connected to the main panel in my basement, where the grid service comes in.

I want to monitor the following:

  • output from the solar array
  • consumption by the EV charger
  • electrical flow on the main line/grid connection
  • few key loads on the main panel

I’m looking at getting the emonPi solar bundle and two emonTX. I would connect one emonTX at my sub-panel, then the emonPi and an emonTX at the main panel. My router is adjacent to my main panel so I can connect the emonPi with an ethernet cable (preferred).

Will this work? Or do I need to connect the emonPi at my sub-panel because that is where the PV array comes in? I’m not sure if the solar bundle is software-enabled, hardware-enabled, or both.

2

I don’t understand what you’re getting at there. “emonPi solar bundle” is just a bundle of components sold as such in the shop. Every component is identical to the parts you can buy separately. Look at the emonPi as a 2-channel emonTx with a Raspberry Pi attached, because that’s exactly what it is. It receives the data from itself and by ISM band radio from the emonTx’s, and makes it available over WiFi or wired Ethernet to a web browser on your phone, computer or whatever. As far as I know, if you give the Feeds (our name for the data that’s stored following initial processing of the Inputs) the correct names, it doesn’t matter where the data comes from for the supplied apps to work.

First, are you on a N.American 120 - 0 - 120 V supply? Because that makes a big difference - all our kit is designed round the normal UK TNCS single phase (0 - 240 V) domestic supply.

If you are, have you looked at the ‘Learn’ page Learn→Electricity Monitoring→AC Power Theory→Use in North America→Use in North America. There’s some useful information there.

Particularly, check your cable sizes before you buy our standard c.t., because it has an aperture of only 13 mm. That’s good up to 25 mm² copper, probably not big enough if you have aluminium service entrance wires (incomers to me). You might need to buy a larger c.t. locally for those.

How many?
Will they be 120 V or 240 V?

If you can fill in a few more details, particularly your supply details, that will help.

3

My question about the solar bundle was seeking to understand whether it was purely a combination of parts at a discount or if there was something different about the software. You’ve addressed that. Thanks.

Yes, my service is NA-standard 240 V rms, as you speculate. The service is 200 A. Each of the three entrance wires are 16 mm in diameter. In addition, I would like to monitor three purely 240 V circuits on the main panel plus one 240 V circuit and my solar PV input on my garage sub-panel.

I appreciate the advice.

4

OK, first point, you should be able to use our “standard” c.t. on the each of the 240 V circuits, but you will need a larger aperture c.t. on the two service entrance wires. You don’t need a c.t. on the neutral - all that would tell you is the difference between the two legs, and if you want that, it’s cheaper to do it in the maths. :wink:

Second, you don’t normally need two c.t’s for the 240 V circuits. Even if those are appliances or plant that has 120 V controls, the current/power drawn by the 120 V part is usually insignificant when compared to the main load, so there’s no real gain in measuring the current in both legs - just measure one and double it (or double the voltage, not both, because you’ll be measuring only one 120 V leg). But of course you must measure both service entrance wires, because the 120 V circuits won’t be balanced.

If you put an ISM band 433 MHz radio in the basement, will another in the garage be able to transmit to or receive from it? In other words, how underground and how thick and what construction are the basement walls? What about the garage walls, and how far away is the garage?

Do you have Ethernet or Wi-Fi to the garage?

This will work IF you can have a radio link between the basement and the garage.

If your basement is underground and you’re unlikely to be able to set up a radio link, then it looks as if the emonPi is a non-starter and you should replace it with an emonBase at a location where you can have a radio link to both the basement and garage, and you have Ethernet. The emonBase is a Raspberry Pi with the radio receiver added (or if you like, an emonPi with no energy monitoring, but it runs on exactly the same SD card and gives you emonCMS). Then you’d want an emonTx in the garage using two inputs (EV and PV), you’d need a further two emonTx’s in the basement on the two Service Entrance Wires and the three 240 V circuits - and you’ll have 3 spare channels unfortunately.
Each emonTx will need an a.c. adapter to measure the voltage and power it, the emonPi needs an a.c. adapter to measure the mains voltage, and it and the emonBase need a good 5 V d.c. power supply.

And of course, you need the c.t’s.

We need to get an expert on the Solar PV apps to confirm that they can be set up with the data arriving from different places, but I’m almost sure that’s OK.

5

Good advice on the CTs. I’ve already used the list on the site to source a CT with a wider aperture.

The router adjacent to my main panel does broadcast a wi-fi signal across the house. The garage is attached to the house and concrete foundation wall between the two locations is probably 20-25 cm thick. The basement is underground and while my sub-panel is only about 8 m straight line from the main panel, the wi-fi signal in the garage is pretty weak. My Tesla will connect to the signal and download updates on that wi-fi signal but the car often shows me one of four bars signal quality. Sometimes two. Will this be sufficient for the emonPi radio? I could route an ethernet cable out to the garage through the conduit that carries the electrical cable between the two panels, so long as the electromagnetic interference from the cable will not mess up the data transmission. I’m not sure about this.

Thanks for your continued help.

6

A straight line between the sub-panel and the main panel will therefore go through the garage floor, through some earth and then through the basement wall. Given a clear path, 8 m is certainly not a problem, but the combination of floor, earth and wall is a different matter.

The Wi-Fi operates on a significantly higher frequency than the ISM band frequency we use (434 MHz), so it’s possible that you’ll be able to use the radios built in to the emonTx and the emonPi, as you get a weak signal at Wi-Fi frequency. Unfortunately, I can’t say for definite that it will get through.

You need to check your local regulations regarding putting a data cable in the same conduit as power. It’s likely that it’s not permitted, or it might require an earthed screen to protect against the possibility of dangerous voltages on the data cable should the insulation have been damaged when pulling the cables in.

I think I’d suggest trying the radio first. If you don’t get a reliable signal from the garage, the first step will be to put a ground plane under the antennas at each end, that typically gives a worthwhile improvement; then it might be possible to increase the signal strength from the emonTx - but that might require an additional 5 V d.c. supply, as the current from the a.c. adapter is limited so as not to ‘dent’ the voltage it’s trying to measure. The final alternatives are likely to be to connect the emonTx serially to a Raspberry Pi Zero W and hope that the Wi-Fi from that is reliable, or lastly the Ethernet cable and a serial to Ethernet adapter at the emonTx end. (Note that although the emonTx has a RJ45 connector, it is not Ethernet, it’s for the temperature and pulse sensors.)

7

Alright, with all of that established, it sounds like I will need two emonTX units (one for the sub-panel, one for the main), one emonPI solar bundle, three CTs from this store, and two externally sourced CTs with a wider aperture. Sound correct?

8

With the 2 × 100 A c.t you get with the Solar bundle, that gives you 5 c.t’s good for 13 mm diameter wires (Solar + EV + 3 on main panel), plus the two for the 16 mm service entrance wires.

Don’t forget to add the power supplies for the emonTx’s.

I’d also strongly advise you to add a programmer. It might or might not be necessary, depending on the other c.t’s you buy, but in any case if you do need to update or adjust anything else in the emonTx’s software, you’ll probably need one. And depending on the cost of carriage, it seems hardly worth not adding one.

So let’s just hope the radio gets through.

9

Order placed. Thanks for all of the assistance and patience.

1 Like
10

No problem. I’d much rather try to get it right at this stage than see a disappointed user when they find they’ve misunderstood something.