Can I get closer to zero?

I always use a little bit of grid power in a week - even when it’s sunny as it has been lately. I don’t lose sleep over this, but I do wonder about it sometimes, and it seems that nothing I can do will bring that figure down.*

Obviously when we have bad weather the figure goes up. But for the week just ended the usage as per the municipal meter is 1.54 kWh per day. Data from SEMS (the Goodwe portal) suggests 1.38. I assume that difference is the little bits that the inverter sends back from time to time, even though it is set to not export.

Here’s yesterday’s graph. The orange line is the municipal feed. When that line goes down I’m buying, when it goes up I’m selling. It looks flat most of the time, but the tool tips you can get by letting your mouse pointer hover over a point on the graph tell a different story eg

And if I move the mouse around it seems the system is nearly always buying or selling, not a lot, but it’s never a nice round number.

Turn all the other traces off and you get the ugly truth

There seem to be three distinct periods where the buying gets a little heavier

  1. In the middle of the night. Looks like the inverter shuts down when the loads are very low. So you get these periodic dips of the orange line. I was told that this is the way that Goodwe’s work, and one way around it was to keep up the overnight load. So I now have external lights on all night. But they’re all LED, make very little difference to the load, and the behaviour perists.

  2. When the system is transitioning between no sun (that the panels can use) and sun. So, for this time of year, about 15:30 to 17:00 (half my panels are East facing) and about 7:00 to 7:45

  3. When there’s a sudden increase in load - but not always. Sometimes turning the kettle on will prompt the inverter to draw from grid. Or maybe everytime, but the graph data is not granular enough to catch every instance.

Over the life of the system, fair weather and foul, this draw from the grid averages about 2.5 kWh per day. Which doesn’t break the bank, but also I don’t mind saving a bit when I can.

*One thing I COULD do is either use Home Assistant to put it into off-grid mode from about 17:00 to 6:00, or get a timer that can handle 50A to put just after the municipal meter to disconnect for the same time range. Both would actually result in a bit more battery use, thus less battery at sun rise when the system is at it’s weakest.

I suppose some of this is down to the Goodwe algorithm, some of it may be down to the grid responding more quickly than the battery - but then why aren’t there problems during load shedding when we have no grid? So I think algorithm is the real culprit here.

But everybody I’ve spoken to who has solar reports some draw from the grid. Some of it gets blamed on the meter itself, which must consume SOME power. But I can’t see the meter accounting 1.5 kWh a day.And besides, the inverter wouldn’t know about that and wouldn’t record it.

Anyway, I’ve never been able to drive this figure further down. The cost doesn’t upset me really, but surely, when conditions are ideal, I could have a day when I use zero from the grid.

And yes. I could have a common or gardener builder’s express timer and have that use a relay to turn mains on or off. Same effect. I’d rather not have that physically too close to the meter as it may alarm City Power. There’s room in the DB, but I hope the relay won’t hum too much.

And it may just be one more complication.