Things just don't quite add up

First sunny day for what feels like ages and I wondered if anyone could explain what I'm missing?

According to the beta portal. We are generating 701W, we are consuming 2.3kW (tumble dryer is on) and the battery is discharging 1.9kW. I would expect these 3 numbers to roughly add up, but 2300-1900-701=-301W. So where is that 300W going to? At the same time, the inverter shows a 'power now' value of 1631W which if I do the same calculation again makes a lot more sense, 2300-1631-701=-32W. That second value makes perfect sense, but it appears to be showing that to produce 1631W from the inverter, it needs 1900W from the battery. As I was typing I just worked this out to be 86% efficiency on the inverter...I guess actually that seems okay although it would obviously be nice if it was higher.

Edited: Guess I kind of answered my question as I typed it...

judgepd Also the portal is showing figures for a moment in time it is not live data. So it could of collected that data as the inverter is trying to balance generation vs usage vs grid. So for that moment those 300w might of been export just for a moment while it balances.

As an example of a snap shot, my portal says my PV is generating 40.5kw :-)

My ongoing nemesis...the 5 minute update intervals. I would say that I've seen this situation on quite a regular basis so I don't think it's a snapshot issue, it is just the efficiency of the inverter and probably a bit of number rounding in the headline figures too.

Better get yourself some bigger batteries for all that solar!!!

judgepd I've stopped looking at the headline figures and just concentrate on the cumulative totals for the day. Saves me getting annoyed at the 5 minute snapshot being a terrible indicator.

I have a Zappi charger with CT clamps fitted to the solar, battery and the grid. I can update the GivEnergy details at a 5 minute interval and look at the Zappi at the exact same instant. there is always a 100w-200w difference in the power flows with GivEnergy app or portal showing more being used.

I get that there may also be a few seconds lag but I had the Zappi checked for these measurements by an electrician. & they were very accurate.

mjkelly5a I'm due a zappi install on Thursday so I'll be interested to see how much the 2 systems agree or disagree.

mjkelly5a
Hello
I have exactly the same issue, the figures from the portal just don’t add up. It always seems to be about 100w out with the battery discharge figures, this is backed up by the figures from the Zappi app. However, when the battery is being charged via solar, the figures approx match.
Not sure if its something that is a hardware or a software issue.
Regards
M

I have three places I can see solar generation and for yesterday:

givenergy: 4.1 kWh
myenergi: 4.7 kWh
solaredge: 4.4 kWh

It would be nice if they could agree with each other! I'm planning to check this against our solar generation meter at the end of tomorrow (forgot to get the start reading today) and see who the winner is.

judgepd I think a few people are going to reply pretty quickly to me but.... the solaredge is getting data from the solaredge inverter so take this as the correct amount. CT clamps have up to a 5% variance I do not believe they are meant to be exact and depending on position can be more than 5% out as I fud out when my GE system was installed. So with that in mind monitors using CT clamps will never be 100% accurate you data suggestions between a 6 - 7% variance/error across the CT's.

Note this is how it was explained to me, while CT's are sold saying 99.9% accurate it is not always the case depending on other factors.

Useful information, thank you. Also, according to GivEnergy, my solar system generates electricity all night at around 5-10W.

judgepd Only on the GE system it says that? The solaredge reports 0w?

Yes, solaredge shows as zero overnight but givenergy never drops completely to zero.

judgepd Ok I can't explain that one. I thought the PV inverter was wired directly into the GE kit. Well, I tried 😀

I don't believe mine (AC 3.0) is, I think it just uses a CT clamp to pick up the solar generation. Absolutely happy to be totally wrong though.

judgepd that's suggests some current transfer, it could be the least resistive path for the GE inverter to get power is via the solaredge inverter hence the 10w draw overnight.

judgepd So just as a follow up, today was:

Givenergy: 4.8 kWh
SolarEdge: 5.3 kWh
Myenergi: 5.5 kWh
Generation meter: 5.1 kWh

So probably unsurprisingly the winner is SolarEdge, for today at least.

Unless measurement involves a calibrated meter, everything else is an approximation. I've noticed the same with my own clamps for my Open Energy monitoring system, and the readings from my AC GivEnergy Inverter - which is essentially just another 2 clamps when it comes to export/import and solar.

Even the pulse readings from my Met2 smart meter don't help, they are OK if there's no Export, but if there's any export to grid they include that too.

The only readings I know in my system are 99.9% accurate are: the AC Inverter battery data, the Solar generation read via Bluetooth from my PV inverter and the actual 30min readings Octopus provides from my Meter (and visible via the givenergy beta portal which is great); the rest I take as good indications, but with +- 10% error bars.

judgepd Sounds like we have the same system. My generation meter shows the slight variance with the Solar edge.

31st jan - GE 4.21 kwh v Solaredge 4.49kwh Meter 4.40kwh Zappi 4.6kwh