Help with LuxPower system, please - disagreement with smart meter

Astacus

Relatively new to this:

I have a system consistent of 5.4 kW solar generation (18 panels), 12 kWh battery. Recently moved to Octopus GO with the following plan:
As part of this, Octopus installed a smart meter.

Fill battery overnight, so that is full at 4.30am. 
Use battery power from then on, until either there is enough solar to top it up, or run it down. At this time of year, battery  is genrally empty by 2pm, and on a dull day, we're one grid until just after midnight, therefore. Still the charging was cheap!

My big issue is the variance between "Consumption" as measured by the LUXPower system (the orange line, for those who know) and the consumption as recorded by the smart meter.

[nerd alert]. Extracted kWh to user from the Lux system (rather than consumption, though the story is the same) and also recovered the Octopus readings, for January this year. THis is a 'day in the life' of our system ( a grey, non solar day at that). The graph below is a plot over the month of Octopus readings versus Lux consumption readings.

It seems to me that the Octopus readings are typically18% higher than the Lux system.

For example, not shown here - when the panels are working well (say 3,000W or more) we're covering all house needs, and pumping charge into the battery (we've generated 10kWh some days this January), the so-called smart meter is typical giving a reading of 200W continues, which is an added charge to us of 4.8kWh per day.

I have tried power on/power off tests, and I have tried to ensure that the SMART meter clamp and the Lux clamp are not interfering with each other.

But, all my logic tells me it is the Octopus system that is at fault, simply because of the positive grid usage that is beinf recorded when we are making far more power than we need, and directing it to the battery. The Lux monitor shows zero take from the grid at this time.

If any experts can provide insight or advice, I'd hugely appreciate this.

Rob

QrizB

Welcome to the forum.

The smart meter (the white box attached to the wall between your DNO fuse and your consumer unit) will be more accurate than the Lux. The in-home display (IHD) that was supplied with your smart meter gets its data from the smart meter and will be just as accurate.

However, this statement confuses me:

Astacus said:

I have tried power on/power off tests, and I have tried to ensure that the SMART meter clamp and the Lux clamp are not interfering with each other.

The smart meter does not use current clamps. This makes me wonder what devide you are referring to when you say "SMART meter". Can you give more information?

Astacus

Ahh, thanks QrizB. I had assumed the smart meter used clamps, but they were hidden. So, there is none. Appreciate this information. Smart meter pic attached.

This creates a conundrum - two things - one our old unsmart mater, we recorded, pretty consistently, 33kWh/d. It is now quite a bit higher, even at the same time of year.

But what really bothers me is the smart meter showing consumption, even when we can see, in real time, that we've cover all of our needs, and pushing kilowatts into the battery. I just don't get why the smart thinks we're using grid power at that time.

Astacus

So, not only are we apparently using more energy, but this does not take into account that we generated about 350 kWh in the same period

Verdigris

Was your old meter a electro-mechanical one? It could have been reading low.

Astacus

Yes it was. So, that could explain the apparent higher usage now, though I am still perturbed by the 'always using power' response from the smart meter. Are there accurate clamps I could buy/hire to check if the PV system clamp is a little (17%) low

QrizB

I havr the opposite problem (not that it's really a problem) in that my battery inverter exports a few watts continuously and I lose a fraction of of a kWh back to the grid each day.

I don't own a Lux - my system uses a Sofar inverter - but there are plenty of Lux users here. It would be interesting to know if they import or export while running on battery, and how they've managed to strike a happy balance.

One thought though - have you tried moving the Luxpower clamp house-side of the smart meter, rather than grid-side?

Astacus

I think, from the pic above, it is house-side? thanks

Astacus

And yes, we do sneak a smidgeon into the grid from time to time, but it is peanuts - suspect a but of wobble in the control. What is getting to me is that when we are in 'running of the battery mode', there is, according to our Lux system, no flow from the grid at all. Yes, the Octopus meter shows a small, but potential 4-5 kWh/day usage. At least o be fair, Octopus do give yuou access to these data.

QrizB

Astacus said:

I think, from the pic above, it is house-side? thanks

You know your system better than I do but to my eye, you've got the DNO fuse on the far left of the photo, then the tails with the clamp, then the meter, then tails to the isolator. The isolator is meant to be house-side of the meter and I'd expect to see the consumer unit off-screen to the right.

This is what my chart from Octopus looked like back in early October when the weather was good enough that, between an overnight charge and my solar, I could run all day:

The little blips are almost certianly where I was using the kettle as my battery was too small to support a 3kW drain.

Astacus

Aargh - you're right! (my dad was an electrician and I suspect he'll be spinning in his grave!). I've swapped it to the house side! What is achieved by moving it house side? Thanks for calling that.