Help with LuxPower system, please - disagreement with smart meter

Astacus

Thank you everyone.  I had hoped we were being charged for too much electricity by Octopus, However, it seems that the problem we have is the clamp readings to the Lux system. I shall speak to Contact Solar (I have been pleased with them thus far)  and ask them to check the firmware, and also, adjust the clamp reading so that the zero power from the grid is reported correctly and reflects the real situation. At this time of year, it is probably of no huge significance, but when we start generating more power, we don't want there to be a sneaky feed in from the grid. 

Astacus

Non-update: Waiting for Contact Solar to get back to me re the discrepant readings. I'm assuming they can adjust the input from the CT clamp such that it 'understands' that it has to push a bit more into the property to prevent the 200W draw from the grid.

Unrelated: we have a SMETS2 smart meter installed by Octopus, but the IHD reports costs that bear no relation to usage. Not a big deal, since the bills looks correct, but don't the smart meters have the ability to load and use the current tariffs?

Lastly, Octopus are hinting at up to a 75% increase in tariffs in April. I guess I am even more pleased we installed solar now.

We have 18*300W panels (10 due S at about 45 degrees, 8 due W at 45 degrees) and 12 kWh battery (5 * 2.4 kWh Pylontech) through a LuxPower inverter. Even on a sunny day this months, we've generated 10+ kWh (some days 1kWh, however!). We have yet to run the system for the full year, and I am intrigued to see how well we do across the year.

Heedtheadvice

This will not provide an answer, most of the preceeding has probably covered that but I might add things that could be useful in general. I have no specific Lux knowledge.

The supplier provided meters, smart or otherwise, are by design and calibration highly accurate measurement of power as required to meet standards.

CT clamps are very useful and a simple way of measuring current. They are not highly accurate and less so at low current levels compared to the max current capability. Often for domestic use a 100/5 type is used. Max 100amp so not so accurate at 100watts, approx 0.4Amps !!

A clamp measures current NOT  power and this conversion relies on the measurement unit (your Lux or other devices) applying a mathematic formula. That formula needs to use the power factor and voltage. I would guess power factor is seldom used (could be wrong there!) plus real time voltage rather than an assumed figure such as 230volts. Voltage can vary -6% to +10% and still be within spec. so there is potential for error there too.

Devices consume power just operating and that comes from somewhere such as 20watts (my inverter for example with no solar generation) doing nothing. Some devices may show that or ignore it?

There are also conversion/working losses with inverters, chargers etc, hopefully small in high efficiency devices.

Devices have a reaction time. That means there are short term errors such as power supplied not necessarily always matching a demand change often showing as power consumption spikes as well as a slightly longer term problem meeting demand from high power consumption such as kettles etc when domestic generation from solar, battery or both is insufficient. The grid does not suffer that to the same extent and when it does the voltage varies but the measurement by the meter is still correct.

Some devices have a purposely built in delay particularly smart battery charging systems. Some batteries do not like  rapid(ish) switching between not charging and charging and devices can take that into account. As an example a Zappi AC 7kW EV charger (and probably other smart chargers) requires a few second self test, communication with the vehicle and then excess capacity measured for several second before applying charge.

All these things will possibly be there together and so should be considered.

Control based around a CT clamp measurent can be very fast and exceedingly useful but not necessarily the and most accurate method to measure power but often can be optimised in the measurement system.

You can usually rely on a meter but they can also be, like any equipment, faulty!

Astacus

Thanks for that insight.
the residual niggle is why Octopus are reporting a 100 to 200 W demand from grid when the solar is charging the battery, and thus, creating surplus electricity. Surely our take should be zero? I cannot get my head around this!

Ectophile

Unrelated: we have a SMETS2 smart meter installed by Octopus, but the IHD reports costs that bear no relation to usage. Not a big deal, since the bills looks correct, but don't the smart meters have the ability to load and use the current tariffs?

They aren't that smart.  They use the last tariff that was sent to them by the supplier.  But with so many different meters, so many different suppliers, and the DCC as the middle-man between the two, the tariff that a meter thinks you're being billed may not have been updated in a long time.

QrizB

Astacus said:

Unrelated: we have a SMETS2 smart meter installed by Octopus, but the IHD reports costs that bear no relation to usage. Not a big deal, since the bills looks correct, but don't the smart meters have the ability to load and use the current tariffs?

Buried in the IHD sub-menus should be the tariffs and daily standing charge numbers it is using to calculate your costs. Check these against the tariff you're expecting. (If you're on a multi-rate tariff it will probably only be using one of them.)

The same info will be displayed on the screen(s) of your smart meter(s) themselves.

Solarchaser

Astacus said:

Thanks for that insight.
the residual niggle is why Octopus are reporting a 100 to 200 W demand from grid when the solar is charging the battery, and thus, creating surplus electricity. Surely our take should be zero? I cannot get my head around this!

I'm obviously not explaining very well.
Your lux inverter is essentially not calibrated very well, so when you use 500w, it only thinks/sees 300w

So batteries will cover what they think is the house load to bring import to zero by supplying 300w.
Lux thinks all is good, but you are actually still importing 200w.

Now sun comes out and is supplying 1000w, so as the inverter only sees a 300w load, it puts 700w into the battery.... however you are still consuming 500w, so the house imports 200w to match demand.

Your lux is reading 200w of usage/load too little

Astacus

There’s two sides to every dialogue! :-). Its my understanding that is dawdling! 

Now I’ve got it! 

Thanks. I’ll try to get the Lux recalibrated!

Heedtheadvice

Well put Solarchaser with that practical example!

Astacus

Partial update:
First, the Lux Inverter is now reporting bonkers data (120kWh/day usage) but this seems to be an internal issue. It seems to be recording solar generation quite well. Also, the Octopus website is really helpful, in showing patters of usage. This allows me to plot Octopus recorded usage as a function of solar power generated. Allowing for day to day variance, this should have a negative sloe of about -1. And, tadaa! So, there's noise, as might be expected, but basically we're reducing intake by 1kWh for every kWh we're generating.

Unresolved are a) the bonkers readings we're getting at the moment, and b) why the Lux system is allowing precious, solar energy to be pushed into the grid instead of being used to meet our needs/recharge the battery.

More anon, but also, nice to see up to 13kWh in January on a good day (6.5 kWh today with a couple of hours to go).