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Goodwe sending battery power to non backed up loads


Bobster
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Hi all,

I just noticed something that has me puzzled. 

The non backed-up circuits in my house are basically a sub-DB in the out buildings. So when the grid goes down we lose the pool pump, the outbuildings (hence washing machine and tumble drier) and we lose our second geyser. 

The sub-db is fed via a single 32A circuit breaker on the main DB. The 2nd geyser has it's own breaker and a timer switch on the sub-DB.

So in a moment of boredom recently I turned on the 2nd geyser to see what sort of load it pulled. This was on a sunny day with the batteries fully charged and PV derated. The load shut up from a few hundred watts to over 5Kw. Yikes! So I let it run a few minutes, got the data I wanted and turned it off again.

What interests me today is when I look at the graph on SEMS, that the Goodwe not only started drawing as much solar as it could to meet this sudden increase in demand, it drew from battery as well. I thought that as the circuit is not backed up it would have made up the short fall from mains.

So something seems not lekker to me or I have misunderstood something. I know (and have just checked) that when there is no grid that geyser will not turn on. The Sub-DB is dead and nothing connected to it works. That's what I expect.

What I didn't expect is that when there is grid that a non-backed up load will draw from battery as well as solar. 

I am working towards a situation where I can use that 2nd geyser for the guest room if I ever need to. But if it's going to draw from battery then I could exhaust the battery much earlier during the night, and even with a timer switch keeping it on in daylight hours only it is going to draw through the inverter and either reduce SOC or prolong the time the battery takes to get to full charge.

It won't draw from the batter when there's load shedding (as I can easily verify by throwing the municipal breaker), but this on-grid behaviour puzzles me. The pool pump doesn't cause this problem, but the pool pump is 750W and so, I presume, is easily handled just by solar alone.

I am running the Goodwe in "economical" mode.

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Thank you @Brani . Most days the system draws a little from the grid, but I know it has to do that to sync the inverter output to the grid. I use economical mode so that the system will top up the batteries from grid between 14:00 and 16:00 on days with bad weather, and the test fell outside of that time frame. So this all seems logical so far. 

Two things to try then

1) Run it in general mode and repeat the test

2) Repeat the test between 2 and 4 pm with the current settings.

Not just fiddling. Trying to understand how the thing works so as to optimise use of it.

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Posted (edited)
17 hours ago, Bobster said:

1) Run it in general mode and repeat the test

Behaved slightly differently: Drew from grid and from battery. But still a nett drain on battery when I had 2.7 kw coming out of the PV.

It's a 300l geyser with a 4KW element. My electrician says there's no way out of it. Says I can go to a lighter element but it will struggle to heat a 300 l geyser. Said if it was 150 l then there's a win, but not with a 300 l.

Edited by Bobster
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20 hours ago, Bobster said:

Hi all,

I just noticed something that has me puzzled. 

The non backed-up circuits in my house are basically a sub-DB in the out buildings. So when the grid goes down we lose the pool pump, the outbuildings (hence washing machine and tumble drier) and we lose our second geyser. 

The sub-db is fed via a single 32A circuit breaker on the main DB. The 2nd geyser has it's own breaker and a timer switch on the sub-DB.

So in a moment of boredom recently I turned on the 2nd geyser to see what sort of load it pulled. This was on a sunny day with the batteries fully charged and PV derated. The load shut up from a few hundred watts to over 5Kw. Yikes! So I let it run a few minutes, got the data I wanted and turned it off again.

What interests me today is when I look at the graph on SEMS, that the Goodwe not only started drawing as much solar as it could to meet this sudden increase in demand, it drew from battery as well. I thought that as the circuit is not backed up it would have made up the short fall from mains.

So something seems not lekker to me or I have misunderstood something. I know (and have just checked) that when there is no grid that geyser will not turn on. The Sub-DB is dead and nothing connected to it works. That's what I expect.

What I didn't expect is that when there is grid that a non-backed up load will draw from battery as well as solar. 

I am working towards a situation where I can use that 2nd geyser for the guest room if I ever need to. But if it's going to draw from battery then I could exhaust the battery much earlier during the night, and even with a timer switch keeping it on in daylight hours only it is going to draw through the inverter and either reduce SOC or prolong the time the battery takes to get to full charge.

It won't draw from the batter when there's load shedding (as I can easily verify by throwing the municipal breaker), but this on-grid behaviour puzzles me. The pool pump doesn't cause this problem, but the pool pump is 750W and so, I presume, is easily handled just by solar alone.

I am running the Goodwe in "economical" mode.

That's exactly how it works as per design, or as I was told...I had the misfortune of draining my battery bank back into the grid because my settings were not correct with Economic Mode.

I never understood how economic mode actually works, just gave up and went mode 1  with  a battery usage of 10%. At night I set battery usage on-grid to 50% which takes me from 10pm - 7am. then reset to 10% if the weather is bad..In future i'll just drain batteries to 50% to take the extra load...

Can you please post a pic of what your economic mode settings are?

The "economic" mode is for you to charge your batteries at low-cost time and use them at high cost time. There was an article I read last night that shows how Escom plans to charge Solar homes, and it looks like we are going to have to change our habits somewhat in order not to go bankrupt, charge at low cost periods from grid and then use during the day at peak charge times....

https://www.moneyweb.co.za/news/south-africa/how-much-eskom-wants-to-charge-normal-households-and-those-with-solar/

 

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45 minutes ago, FixAMess said:

That's exactly how it works as per design, or as I was told...I had the misfortune of draining my battery bank back into the grid because my settings were not correct with Economic Mode.

I never understood how economic mode actually works, just gave up and went mode 1  with  a battery usage of 10%. At night I set battery usage on-grid to 50% which takes me from 10pm - 7am. then reset to 10% if the weather is bad..In future i'll just drain batteries to 50% to take the extra load...

Can you please post a pic of what your economic mode settings are?

Simple. I have one rule set up to charge the battery at 60% of rated whatever (figure given by battery manufacturer) between 2pm and 4pm. That's it. If the battery has 100% SOC by 4pm then I'm good to get through the night, so that's why I have that setting - it's a hedge against a cloudy day. 

45 minutes ago, FixAMess said:

The "economic" mode is for you to charge your batteries at low-cost time and use them at high cost time. There was an article I read last night that shows how Escom plans to charge Solar homes, and it looks like we are going to have to change our habits somewhat in order not to go bankrupt, charge at low cost periods from grid and then use during the day at peak charge times....

https://www.moneyweb.co.za/news/south-africa/how-much-eskom-wants-to-charge-normal-households-and-those-with-solar/

 

That's for Eskom supplied customers. The picture will vary according to who you buy electricity from. I buy from the City of Johannesburg and they haven't gone this route for the new financial year's tariffs. At this point they don't seem that concerned about solar, and don't make it worth your while to sell back to them.  It only comes into play RE the new surcharge they are introducing on pre-paid meters. You can get that surcharge waived if
a) you agree to the installation of a 20A main breaker
b) You have no solar devices other than solar geysers.

That's so far. The regulations I'm quoting are proposed but not yet published.

They have made provision for IPPs to set up a field full of solar panels or wind generators and sell to the city (but not directly to residences or businesses).

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