Question >>> home energy monitors

Sterlingtimes

If a basic home energy monitor (of the type sometimes given away free of charge by electricity suppliers) with a clamp-on line sensor is connected to a "solar home", will the monitor register just the kW / kWh of electricity provided to the home or will it be confused by the quantity of electricity exported?

tunnel

Hi Sterling..
I have an Eon monitor clamped around the in/out cable(so to speak). The basic model only shows what you are importing(Wh/kWh), which will reduce to zero when you're exporting(works for me) Is that what you wanted to know?
Which monitor are you looking at?

theboylard

As they typically clip on just the import cable (your side of the meter) they will only show import.
I've got a current cost/Eon monitor that only registered import.
I've also got an Owl with Intuition PV, a Wattson Solar and I've got a GEO Solo PV that came with the solar install.

So far, out of all the toys I've got, I've still not found my gadget nirvana!

I keep looking at Openenergymonitor.org but they keep moving goalposts! I'm waiting for a release date for their RasPi based emonPi standalone solution, which should be next month.

I've also contacted one of the forum members who built his own version several months ago, waiting to hear if he is going to market his.

EricMears

theboylard wrote: »

As they typically clip on just the import cable (your side of the meter) they will only show import.

A 'clip on sensor' will show the magnitude of current passing through the cable around which it's been clipped. It won't show the direction of the current flow.

If you can arrange your wiring circuits such that you know that only imported electricity is running through a particular section of cable then the quoted sentence would be true. However, inverters are generally set up to export electricity into the same cable along which imports arrive (and the constraint to shut down when the mains fails pretty well obliges that situation).

A 'clip on sensor' on the cable that joins the meter to the consumer unit will therefore register the nett current but (without some additional electronics) won't tell you whether that is a net import or net export.


The Wattson Meter (& no doubt some competitors) is set up to measure generation from the current flow through the TGM circuit and usage from a point inside the CU where generation current can be excluded and do some simple arithmetic on those two values to produce a net current of known sign.

Sterlingtimes

Thank you, tunnel, Eric and theboylard for your answers.


I think that the answer then is that the meter will read the net current flow (always positive) >>> import minus export.


So my current position is that I can see my solar generation at the Enphase site >>> public view here:


https://enlighten.enphaseenergy.com/pv/public_systems/2y7S502614?preview=1


I can read the export dump to the immersion via iBoost.


I can only read my import via the main mechanical meter.


So there is some information that I am missing.

EricMears

Sterlingtimes wrote: »

Thank you, tunnel, Eric and theboylard for your answers.


I think that the answer then is that the meter will read the net current flow (always positive) >>> import minus export.


Rather than 'always positive' you should be saying 'unsigned'


So my current position is that I can see my solar generation at the Enphase site >>> public view here:


https://enlighten.enphaseenergy.com/pv/public_systems/2y7S502614?preview=1


I can read the export dump to the immersion via iBoost.
I can only read my import via the main mechanical meter.
So there is some information that I am missing.

The main mechanical meter will indeed show what you're importing. They're not usually very good for short term results though if you have a really old meter with tenths & hundredths of a unit and a reasonable stopwatch (or phone app) you can get a good idea of instantaneous results. If you do that and can get your inverter output then you can calculate the amount of electricity you're using.




Or of course, if you have an iBoost, whenever it says you're heating water you can't be in a net import situation so if the clamp-on meter shows a reading (the iBoost will of course be trying to make it read zero !) then the figures will be an export. If the iBoost says you're not heating water then any clamp-on reading must be a net import.

mnbvcxz

I have an old owl monitor on a cable. It shows how much I am importing or exporting but does does not say whether it is positive or negative.

So if it reads 2kw I might be importing 2kw or exporting 2kw. It can't tell.

I have a second basic monitor (£10 off ebay) on the inverter cable which tells me how much I am generating.

By looking at the two I can generally make an educated guess as to whether I am importing or exporting, though it is by no means ideal.

If I spend £80 on an owl pv it would tell me if the number was positive or negative but I have not felt that was worth it.

Sterlingtimes

mnbvcxz wrote: »

By looking at the two I can generally make an educated guess as to whether I am importing or exporting, though it is by no means ideal.

Funny, I have been thinking through the same issues over the last few days. The Owl looks useful, but some users are questioning the accuracy of the results. All in all, I can see my generation from the Enphase site, and I rely upon the mechanical meter for importation. The iBoost is helpful in indicating when export is occurring.

Now, Mrs Sterling's tumble dryer and washing machine are under intense investigation (both metered). I need to get a fix on the extent to which they are contributing to the electric bill.

EricMears

I wired our house to include a 'split load consumer unit' so that almost everything in use is fed by the RCD side of the CU. Only exceptions are smoke & burglar alarms (negligible usage) and a couple of lighting circuits (obviously not used when SPs are generating). I was therefore able to reroute the cable that supplies a live feed from the non-RCD side of the CU to the RCD side and can therefore measure power in use with a clamp on sensor around that cable.


My Wattson meter therefore uses one sensor on the inverter cable to measure generation and another (described above) to measure most of the consumption and since the Wattson allows an additional input on the consumption side I've got another sensor on the feed to the UPS (which of course is fed from non RCD side of CU). The net reading of the Wattson should therefore be reasonably accurate

zeupater

.... and if either the customer or the installer thought about the problem before the installation the inverter could have been connected to a separate small CU (garage type) with the metered supply split by a Henley block - you would then have the ability to spot measure generation, consumption or a net figure as required with any simple clamp based monitor just by locating the clamp appropriately (or perm whichever combination you want !)

Regarding accuracy of the OWL, they're probably just as accurate as any other clamp based monitor if setup correctly .... We can check accuracy by balancing reported generated power to reported total power consumption and check the accuracy at the meter (ratchet wheel balanced) so I know how accurate our OWL monitor is, however, I'd still only use a monitor as a monitor, they're not meters - but you've already got enough of them for what you need (generation & import) , and if you really need to measure export accurately it could be done without too much expenditure (~same cost as a TGM & a little labour) ...

HTH
Z

1961Nick

The Geo Chorus II was expensive but I've been pleased with it's performance. It uses sensors to count the import & export meter pulses in addition to a clamp on the meter tail.

The generation & import figures are 100% accurate. The only time it's slightly inaccurate is when it uses the clamp sensor to calculate the solar use during export.

When pv generation is low (<50w), there's a software glitch that causes it count some of this as an export (understating the solar use).

Overall 8/10
(I'd give it 10 if it wasn't for the cost & the iffy software)