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Off-Grid Trial For August/September 2022


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3 hours ago, WannabeSolarSparky said:

Fortunately I still have my Growatt spf5000ES that I should actually hook up into my system and reconfigure exactly how I have everything wired up.
Ideally for Off-Grid I should have 2 of the growatts.

Probably better to go for 2 x 5kW Axperts models which can run on solar only when the grid is not present. This way with dead batteries, you can still have power. 

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Just cannot ask for a better day to do these tests :)
Day 3 going pretty well and had the timers set nicely to keep all the loads nicely within the inverter specs :)

Been "loadshedding" since 7:24 this morning.
Geyser came on correctly this time, I also set the crypto rig to switch off when the geyser comes on and to switch on again when the geyser switches off :)
That left plenty power to allow me to run the kettle or toaster while the geyser was charging :)

With all the use through the day the battery has also managed to fully saturate by 15:10 :)
The automation even switched the one crypto rig back on to use the extra solar that's still left for the afternoon after the batteries got to saturation point.

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5 hours ago, WannabeSolarSparky said:

On the batteries side you should aim for a minimum of 400ah to even consider a move to going fully off-grid and even then you would need to carefully manage your usage to have reserves for those cloudy days.

This is the truth. We've just had an overcast day in my hoekie of Johannesburg, and my system serviced all the loads but the battery was nowhere near 100% when the PV started tailing off in the PM.

To be off grid, you need the battery capacity you mention (double what I have) AND the panels and inverter(s) to charge them in reasonable time. Plus, as you note, the discipline to manage your large but finite resources.

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6 hours ago, WannabeSolarSparky said:

2x 100ah batteries are just not going to be enough to go fully off-grid.

Yip, I have a base load of 1.2 kW, and would need at least 40 kW of batteries to go off-grid. With 20 kW of batteries, I could "limp" along off-grid, and maybe use the generator to help if needs be. To go off-grid on a small solar system will require to many sacrifices for most people.🤔

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11 minutes ago, TimCam said:

Yip, I have a base load of 1.2 kW, and would need at least 40 kW of batteries to go off-grid. With 20 kW of batteries, I could "limp" along off-grid, and maybe use the generator to help if needs be. To go off-grid on a small solar system will require to many sacrifices for most people.🤔

Correct, my wife and I both are already very very low power users (since we started with solar a few years ago we started adjusting how we do things)
We are pretty much at our limits with what we are willing to sacrifice as apposed to what we gain from solar. Any further and it would no longer be fun to use solar.
Currently with these last 3 days of testing we have brought our eskom units down to less than 1 unit per day, that in our books is already a massive WIN :) and we have already gained massive insights into how far we can still push our little system.
Now to simply keep adjusting the system and maybe adding 2 more batteries and hooking up the growatt then by the time eskom make up their minds how they are going to do the feedin tarrfis and fixed fees then we should know if we are going to go Full-off-grid or feed in to the grid with a few extra panels to negate any fixed fees :)
In my books either way we win :) for a small added outlay.

Edited by WannabeSolarSparky
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14 hours ago, WannabeSolarSparky said:

Still ended up having a bit of wastage this afternoon once the batteries reached saturation point.

I have noticed you use battery voltage in your graphs. Do you not have SOC available? I have noticed that voltage is a pretty useless metric on my battery. The SOC % works much better 

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Just now, iiznh said:

I have noticed you use battery voltage in your graphs. Do you not have SOC available? I have noticed that voltage is a pretty useless metric on my battery. The SOC % works much better

Let the debate begin :)

SOC as reported by the builtin bmses on LiFePo4 factory built batteries is not a good reflection of the actual state of the batteries.
Especially considering the crappy bmses these factory built batteries come with.
Voltages are a bit closer to reality (In my case anyway)
The correct way is to use a decent coulomb counter on each battery, I have not had time yet to get mine setup on each battery, also still waiting for some parts from china to complete that.

Or a decent BMS :) like the jk bmses, but with these factory built batteries you will void your warranties.
And stock in SA for them is scarce, also waiting for mine to arrive from China  :)

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43 minutes ago, WannabeSolarSparky said:

Voltages are a bit closer to reality (In my case anyway)

and even then you have to question the accuracy.
The average user accepts what's presented from a single source. For most that would be the Inverter. 

And on closer inspection you find that the V reporting is not even accurate. Which value do you trust. The Inverter, the battery BMS?
Take a Fluke just to find out that none of them are correct.
Here is an example of a bit earlier. The two snapshots were seconds apart. Compare the Inverter and Battery BMS values. 52,7V vs 53,3V

Just before the battery hit 100% I checked again. Inverter 53,6V  BMS 53,4V and then I used the Fluke on the Battery terminals and that was floating between 53,1 and 53,2V.

So it becomes a selective choice in terms of whichever reading makes you feel good. Does that make any of the readings correct? Definitely not. The Manufacturer will of course use whatever the BMS stored when it comes to warranty claims. The fact that your best AVO can prove that their BMS is not accurate is an inadmissible argument from their perspective.

 

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6 minutes ago, zsde said:

The average user accepts what's presented from a single source. For most that would be the Inverter. 

And on closer inspection you find that the V reporting is not even accurate. Which value do you trust. The Inverter, the battery BMS?
Take a Fluke just to find out that none of them are correct.
Here is an example of a bit earlier. The two snapshots were seconds apart. Compare the Inverter and Battery BMS values. 52,7V vs 53,3V

Correct, most of the time for the average user it is what they are comfortable in trusting/relying on.

Myself being a big DIY enthusiast and tinkerer of note, I prefer the trial and error method to find what works best for me.


I am also a BIG fan of Andy's Off Grid Garage and he has shown, by demonstration, a massive amount of info on how these LiFePo4 batteries work and how to get the most out of them without destroying them :)

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30 minutes ago, WannabeSolarSparky said:

I am also a BIG fan of Andy's Off Grid Garage and he has shown, by demonstration, a massive amount of info on how these LiFePo4 batteries work and how to get the most out of them without destroying them

Also love Andy's channel.

I have a 16S2P (200Ah ... that is more like 240ah DIY battery with a Daly 200A BMS). The current shunt to measure the SOC works pretty well. If I throw 60A charge current towards my battery and it is pretty full (75%) you will find that the cell voltages will rise towards 3.40 - 3.55V. Overall voltage will measure close to 55V. When you limit the current to 10A then sudden battery voltage drops back to 53-54 volts. The voltage appears to be a function of the direction of which you letting current flow and how much current is flowing. The moment I put a load on the battery the 3.5V cells are back to 3.35V and the battery shows 52-53V. I cycle my battery between 40% and around 80-90%. On good days I might hit 100% (but the winter sun angle limits my production). Trying to cut Eskom out of the picture but every now and then I still need to buy a unit here and there

 

  

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2 hours ago, TiaanSmit said:

what has been your average kwh production over the past 3 days?

@TiaanSmit it has averaged out to 676 watts per hour. That is measured continuously from 26/7 6am till 28/7 17:50

My essential loads over the same 3 days time-frame averaged in at 539 watts per hour.

Today to the right on the chart also show that picture perfect cloudless days are NOT perfect for solar :)

Also noteworthy from the chart is that there is not really too much difference between West And East facing panels.
Another takeaway from the data is that my 8 connected panels are NOT enough to power my loads and fully charge/saturate my batteries over the same period of time.
Need to add in my 2 extra east facing panels, but I suspect even that will not really be enough to keep the batteries correctly saturated. May need to add another 2 west facing.
And if I eventually add in those 2 missing batteries then I would need to almost double up on the panels to get the same saturation levels.

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Ok some more tweaks to happen today.
I am moving the geyser back to the non-essentials side.
The sunsynk 5kw just not suited to have that heavy load connected. It leaves way too little room for other appliances like my kettle and toaster which is essentially my essentials :)
Also trying to finish the frame for my 2 missing panels to be added into the east string :) I really need that extra 1000watts for the battery charging.

Edited by WannabeSolarSparky
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