After PV system installation, power consumption went drastically UP

[Goodi]

Hello,

My parents-in-law had a PV system with battery installed in September.
Before the PV system was installed, they had a power consumption of about 1500kWh to 2000kWh per year.
Afterwards they had a consumption of almost 800kWh in October alone. They are now already up to almost 2MWh since the installation.
And that's not just what the inverter is showing, they also got a horrendous bill from the power company.

I'm an EE engineer but my world is PCBs and high speed digital.

My mind struggles to understand how the system can appear to work properly and still cause this sudden increase in power consumption.
Any idea what could cause this?

Thank you very much in advance!
Greetings
Stefan

[coppice]

My guess is something has been reversed in measuring one of the current flows. Maybe a CT is clamped on a cable in a reversed manner, or two terminals have been swapped somewhere.

[nctnico]

There is zero export! Likely a problem in the metering

[Goodi]

As far as I know the system is not allowed to export power to the net. That's why.

[coppice]

There is zero export! Likely a problem in the metering

Why would they want to export anything, unless they have a massive surplus? There are batteries in the mix.

[Goodi]

But as I said also the meter of the power company shows increased consumption, thus the increased electrical bill. And as far as I know nobody touched anything there. The system is also not allowed to export power.

[coppice]

But as I said also the meter of the power company shows increased consumption, thus the increased electrical bill. And as far as I know nobody touched anything there. The system is also not allowed to export power.

Can you turn off the breaker from the PV panels for a couple of days, and see what that does to the numbers? If it doesn't restore the import to historic values it should tell you a lot.

[KE5FX]

Or walk around with a thermal cam.

[nctnico]

There is zero export! Likely a problem in the metering

Why would they want to export anything, unless they have a massive surplus? There are batteries in the mix.

But it is only a 5kWh battery by the looks of the daily charge capacity. That does nothing and it looks like this is a PV system somewhere between 5kWpeak to 10kWpeak which gives a massive surplus. My guess is the system is exporting (despite that it shouldn't do that) and the meter is adding imports and exports.

Another problem can be with the PV / battery inverter and the loads connected making the meter measuring wrong. Smart meters can be prone to that. Putting a good old (passive) meter with a rotary disk in series with the smart meter can be very useful to detect whether the meter is working correctly or not.

[rteodor]

If the meter is simple one without separate counters for import/export: follow the meter indication by hour and check if "consumption" increases while the sun is up compared to night time (or if the battery is empty). That should give a hint if there is an "unexpected export".

A clamp meter could be useful too to check what's coming from the grid vs. actual house consumption.

LE: But by the look of the daily variance, the "unintended export" is the most likely explanation.

[Siwastaja]

First make sure you have proper contract with grid/energy company for export; selling them your excess energy. You must have done that, right? Sure at that point someone also checked that your utility meter is capable of metering the export, right?

If that is taken care of, then make sure it works: get hourly metering data from the energy/grid company (sure it must be available online to you in year 2024 in Austria, yes?)

This must mean two numbers, export and import. Compare both to what the inverter application says, to rule out energy metering error.

Specifically check if there was any sunny day when you remember that battery was already showing 100% at some point in afternoon. Then there should be export. Verify that the export is recorded correctly both in the inverter and in the grid/energy company operator data.

Batteries are nasty in that they totally destroy your energy consumption if anything goes wrong with metering. In other words, the energy flow (direction and magnitude of power flow) the inverter sees MUST match what is measured by utility meter, pretty closely - especially close to zero.

And metering is not made easy by e.g. Chinese inverters having an overcomplicated system where a separate box is wired with RS485, then to that box is connected all three phase voltages and three CTs and the order of the phases must match as well as direction of CTs. Too many possibilities for installers to make a mistake, and mistake is hard to see, there is no intelligent diagnosis.

It is also important to know what is the netting period your grid company uses. This varies from milliseconds to a year depending on where you live and what kind of contract you have! And while of paramount importance, it can be nearly impossible to know what it is, you need insider information. For example, I know this is 15 minutes in most of Finland now, but I have no idea how I would Google that or where I would get that information as a consumer. Inverter net-zeroing feedback loop frequency response is somewhere around 0.1 - 0.5 Hz, so for netting periods shorter than a few minutes, extra cost is caused by timing mismatch. Also if phases are not netted together in a 3-phase system for billing (which was the case here still a few years ago!), it will totally ruin everything (inverter keeps total power at zero, which means some phases export while others import; if you are billed for the phases separately, you pay even at zero power).

Also see https://www.eevblog.com/forum/renewable-energy/low-power-efficiency-regulation-of-battery-hybrid-inverters-(eu-and-otherwise)/ - increased power consumption is to be expected.

I would suggest not to get grid-tied battery inverter systems without third party management system (aware of hourly energy prices; maybe participating in reserve markets). For PV timeshift only, it is not worth the investment, and extra power draw negates large part of the effect.

[Siwastaja]

There is zero export! Likely a problem in the metering

Why would they want to export anything, unless they have a massive surplus? There are batteries in the mix.

"Typical" 6-10kWp PV system of today produces some 30-40kWh a day, while typical battery size is 5 to 10 kWh. So most still goes to export. This is why for example our control algorithm often chooses to export even at very poor price (say 1 cent/kWh), if it is known from weather and consumption forecasts that battery would become full anyway, and forced to export at even worse price (say 0).