I have a Goodwe ES.

How does this decide when to use grid and when to use battery?

Looking at the graph for today, the water heating (heat pump) turned on at 4:30 am and ran for 25 minutes. The load peaked out at about 1.7 kw. All of the load, for the entire 25 minutes was serviced by the battery.  SOC dropped down to 54%. My system is set up so that it will not let the battery discharge below 40% unless there is no grid. So at this point I have plenty in hand.

At about 5:15 I used an electric kettle (I know). The peak on the graph is about a kw and the system drew half a kw from grid.  SOC was 53%.

So this is odd to me (emphasis on "to me"). Why was the system happy to let the battery service the heat pump unassisted for 25 minutes, but decided to use grid power when the kettle gets turned on.

Later in the day with the battery fully charge, our housekeeper did some ironing. It's an overcast day, so not a lot of PV available. Iron is drawing 1.2 kw at it's peak, mostly about 800 w. Again the system uses grid and will not touch the battery.

OK... this is not going to break the bank, but I am puzzled by this. Why does it draw from battery some times, grid at other times? I thought it might be momentary spikes causing the grid demand, but surely there's a spike when the compressor for the heat pump kicks in?

The heat pump is backed up. The kettle was on a socket that is backed up. The iron I'm not sure... depends where she was working. 

 

5 minutes ago, Bobster said:

Again the system uses grid and will not touch the battery.

I have the same inverter and it shows the same behavior. It takes quite a while for the inverter to switch over from charging to discharging the batteries. If the duration the load exceeds the available PV power is to short it will never go into battery discharge mode and as a result uses the grid to make up the shortfall.  

3 hours ago, Fuenkli said:

I have the same inverter and it shows the same behavior. It takes quite a while for the inverter to switch over from charging to discharging the batteries. If the duration the load exceeds the available PV power is to short it will never go into battery discharge mode and as a result uses the grid to make up the shortfall.  

But mine drew from battery quite happily at 4:30. What I need to check is if the solar panels are on (ie output > nothing at all) when it starts drawing from grid. That was certainly the case this afternoon. But at 5:15 in the morning in Joburg... 

On 2019/11/01 at 7:40 PM, Bobster said:

But mine drew from battery quite happily at 4:30. What I need to check is if the solar panels are on (ie output > nothing at all) when it starts drawing from grid. That was certainly the case this afternoon. But at 5:15 in the morning in Joburg... 

... well maybe. This morning by 5:25 I was generating PV. So my panels were "on" though not yet ready to light up the suburb. And they'd have been on a few minutes before that, I reckon. "On" as in the Goodwe can detect them, even though they're not doing anything particularly useful.

So it seems once the panels are on (which is a binary thing - they're either on or they're not) then it does everything it can to charge and protect the battery.