Transient exporting

The past few days I have noticed that during the day my system frequently exports power (sometimes significant amounts - 3kW ish) for short periods, rather than put that power straight into the battery, despite the battery SOC being very low.
The system is set to "eco", i.e. dynamic balancing to keep grid import/export to zero. It seems to happen more when strong sunlight is being interrupted by clouds then returns - is this just the inverter taking its time to get things back into balance? I have not noticed this before, could a firmware update have changed things? Is it the sudden change from around 300W to 3.5kW+ of panel output power? I note that around 1kWh total is being exported per day, in these transient bursts.

Anything I can change to minimise/eliminate this?

wilfleek Funny you should say this as I have been contemplating posting something very similar. Happens on my system too, exactly as you describe. After the spike of grid export I quite often also get a rebound spike of grid import. Throughout the whole episode solar generation remains well above load and all I would have expected to happen is the rate of battery charge to fall a bit and then recover. As you say it only seems to happen in strong sunlight and similar sharp drops and rises of PV output do not initiate the grid spikes when the sunlight is weaker.

I guess the first question is where are you getting the data/figures from?

As the GE portal info only updates every 5 minutes it's not a great source.

I've shifted the Myenergi CT clamps around so I get 5 second updates from their side and it does show some minor import/export fluctuations during load changes. That said looking at my 30 minute octopus data is not even showing on there

You can see the export happens on mine. It’s been pretty active today due to the rapidly changing pv generation, but it’s just to trim the load as the inverter can’t react quickly enough as you more than likely know.

Bugger forgot you can’t add images without an external source. I’ll add one in a minute.

So does anyone know what the inverter response time is, and how it might be affected by the size of the incoming Solar generation?
Today we (according to the portal) generated 8.9kWh, and exported 1.1 kWh. which is a not insignificant proportion of the total. Admittedly it was swinging from 400Wp to 4kWp as the clouds scudded past.

My system is only 2kW - today it generated 2.6kWh and exported 0.2kWh. Typically we'll export 0.1kWh or less but today it looks like the sun was very intermittent (I'm away at the moment, but I do 10s sampling locally and save it in InfluxDB). 1.1kWh of export seems a bit high but may be reasonable especially if you've used anything like an iron or modern oven, which will cycle on/off once up to temperature and normally will cause some more export if the battery is providing power. There is other discussion previously in this forum about the response time - but in my experience it's about 10s.

I think there may be more to this than the recognised inverter lag. In average levels of sunlight it appears that the inverter reacts to sudden changes in solar power in a similar way to changes in house load. There is a short delay in fully adjusting to the change which results in a small amount of unwanted grid export or import. When sunlight is strong however, a sudden change in solar generation gives the appearance of the inverter momentarily shutting down; resulting in zero battery charging and a large spike in grid export/import.

Woodstock This was/is my suspicion - the inverter seemingly behaves differently when the swings in solar generation get larger.

anglefire Nearly a couple if minutes 😉

Hi as soon my inverter sees a cloud and a rise in export it drops the battery charge to zero, then the momentary cloud clears and I'm exporting circa 3 kWs to the grid for about 35 seconds until the charge ramps up to 3kW. It does this continually seems to be exporting more than importing when it is a variable/ cloudy day. I would love it to ramp up and down in a more controlled manner rather than dropping the charge to zero then going through a lengthy period ramping up only to drop off again. P.S. Monitoring once per second

Guzz I would be interested to know if the strength of sunlight affects whether or not the inverter drops the charge all the way to zero. I only have the five minute reporting of the beta portal to go on but it appears that in average sunlight the inverter just lags a bit, producing a low grid import/export ripple, but in strong sunlight it stops charging completely resulting in large (several kW) spikes of grid import/export. What I am observing may just be a feature of the five minute beta portal reporting but if you are monitoring once per second you can perhaps see if the behaviour of the inverter does actually change according to sunlight strength.

It seems a slow change in solar production sees the inverter ramping up and down nicely, however when a sudden change of perhaps 300 or 400 watts occurs the inverter drops to zero, despite still exporting perhaps 2kw, it then waits there for approx 35 seconds then slowly ramps up until it using all the surplus to charge the batteries until another cloud/ or sudden change in production then again drops to zero!

It seems this truly IS a "transient" issue, so I am going to stop worrying about it. As I also have come to realise that in just a month or so's time, we will be generating more each day than we can use or store, so I have signed up for Octopus agile outgoing. I'll report back here about that when I have some data, might be a few months!

I went to agile outgoing on the fixed tariff- now 7.5p.
I exported 0.1kwh yesterday due to transients. My solar was the best day yet at 6.2kWh. I think that should improve daily now the sun is being higher and start to miss the tree - in similar circumstances

I Exported 3.33kWh yesterday. It was windy with many clouds often causing many quick changes in PV output.

anglefire I thought that rate was now down to 5.5p? Maybe that is just in my own area? That is why I decided to have a punt on the agile outgoing version. You can apparently switch between fixed and agile, no problem.

I had an email from them the other day saying it had gone up.

I understand that their "SEG" rate is going up, but I think that is a different thing from their"outgoing" tariffs.

wilfleek I could be wrong but I think they have 3 SEG/Outgoing tariffs.

1 @ 4.1p for those on Go
2 @ 7.5p standard rate SEG
3 @ Agile goes up and down but I think currently averages 18p

There could be more, but those are the 3 I know of.

Not exactly straightforward, is it?

wilfleek Its not too bad, if you google SEG providers several pages will give you a list showing their current rates. But companies do various deals like EON do 12 months at 5.5p if you buy a solar system via them etc.

Guzz

Some previous discussion on this very behaviour here so it seems like it's "normal"

chrisdev Thanks Chris for highlighting this for me

Just to add, I experienced this problem again today due to transient clouds. The battery stopped charging (and I was exporting) for so long, and so much, that my Zappi saw that as surplus and started taking it for the car! That means the battery wasn't charging when more than 1.4kW of power was available for 30+ seconds.

yandards My MyEnergi CT clamps definitely show a transient export as does my GE CT clamps. it is definitely happening and I'd also like to know why.

chrisdev I've still to learn how I use my Zappi when my 3.2kw array starts to max out, the battery is full and my car needs a charge. I can set the battery to a max % level and the excess can go into the car OR use the granny at 6a shoving 2.4kw into the car balancing it that way.

Not sure the Zappi MGL will be able to handle the above out of the box without discharging the battery. Will it pull the extra out of the grid or the battery?

I had a new SolarEdge fitted in November so i am expecting to see more power.

My installer told me that MyEnergi & GE where working on some form integrating of both the systems. I keep asking the question but not getting an answer from either company.

mjkelly5a Zappi is a bit hit and miss if you want it to work with solar only during cloud cover.

The Myenergi forums suggest that most EV manufacturers have coded in a dropped charge reconnect limit counter to stop the car being damaged by a dodgy charger - I know my E208 allows 10 events before it stops any further charging.

I've had the car lock out the Zappi in the last week preventing it's overnight scheduled charge working which isn't ideal. It did tell me when I checked the app but the status is 'charges delayed' not the clearest.