jykenmynie

It isn't necessarily obvious to me what they mean here with the MPPT voltage range. Perhaps it is simply the range the MPPT would search for the maximum power. The moment you put some load on your panels, the voltage would drop well into the MPPTs range. That can't be the problem, surely...

Can this inverter blend power sources? It might be that the demand for power in your house is too great and the inverter has to use the batteries because the solar isn’t enough? Have you tried with very low demand in your house?

Maybe you can get someone to borrow you a oscilloscope (I think you can use them like this, maybe there's something else you can also use) to measure exactly how long the transfer time is. At least that should help you clear up whether maybe the PSU is the issue or maybe it is your specific inverter. I can't imagine it being the inverter, because so many people have them.

If you couldn’t properly charge the batteries due to rainy days or so, you might well. I’m not sure what the self-consumption of those Axperts are, I’m guessing 50W. You could have also had loadshedding in between the sun’s availability for which the batteries could’ve run down all the way to 42V.

Yes, the inverter would draw about 50W continuously from them.

How did you use the batteries? Did you cycle them daily/only for loadshedding? My guess is that if you cycled them daily to 42V for a year, I won’t be surprised if they are dead. I’m assuming that 42V on AGM is a very low SoC. My understanding is that AGMs never be drained to less than 50% SoC? That said, I don’t know lead acids myself at all.

Not sure about the exact model Corsair that you've got, but the RM range, for example, has a hold up time pretty close to 20ms. Guess it would also depend on the size of the PSU compared to the draw by the components at the time. That said, my wife's PC has an RM650 in and mine an AX850, both held up fine when our MP II transfers, so far, so that is probably not the issue for you. Do you suspect the MP IIs are transferring too slowly?

If your PC don’t have a good PSU I guess this might happen, so never cheap out a PSU when your country don’t have a reliable and clean grid. Get one with good capacitors. It protects your sensitive electronic equipment.

And also ~10% DC to AC conversion loss will give you ~6.9kWh on the AC side.

Just something to consider: In my opinion you are significantly underspeccing on batteries. Why do you need 15kVA of inverters? If you need it because your demand is that high, you need at the very least 15kWh of Li batteries, but preferably much more if you go Pylontech. Their BMS is strict against abuse and are happiest at 37A continuous discharge. Do you really need three inverters? Isn’t a good hybrid inverter a better option (I don’t know your specific use case, just asking).

Just remember that no battery would keep its full capacity over its life. IIRC you can expect these batteries to end at around 60% original capacity. So on average: 2.4 * 0.8 (adjustment for average original capacity) * 6,000 * 2.1 = 24,192. You need to compare that against the battery's price. As long as Eskom's price increases are in line with what a risk-free investment would have earned (say keeping your money in your bond), then it future increases would have no impact on this calculation (although you can argue that you have hedged out uncertainty about what those units will cost you, which does have value). Depending on your municipality, electricity could have a different price and you could also be charged more or less after a certain amount of units. For me: Buying my batteries (and consequently an inverter) on its own wasn't as much an "investment" in electricity cost savings as it was an "investment" in being able to be hedged against loadshedding. I decided that having the predictability of my evening routine is worth at least something to me. So it was a luxury purchase that require no further justification. Purchasing solar panels was therefore the only cost I need to factor into deciding whether the electricity savings is worth it to me as an "investment".

I won’t call lithium “settling”, because it seems to be the best all round option for solar systems at the moment.

So wouldn’t the same voltage relate to the same SoC always? Even if the voltage curve is quite flat, after you have established what voltage relates to 90%, can’t you use that? You can establish it with communication with the BMS originally, and then only charge to that voltage from that point onwards. Only problem I see is sell balancing?

This is not my understanding of how a Victron would charge a battery. I am able to set the voltage to which it needs charge the battery and the Venus effectively overrides what the BMS wants to do. For example, I am only charging my Pylons to 52V at the moment. I understand this is enough for the balancers to kick in and get reasonably close to 100% SoC. The only problem I think there is to charge to less than 100% SoC is because you run the risk of not getting the cell balancers to activate (which is a big problem if you intend on never taking it to 100%, because my understanding is that the cells would become unbalanced over time).

Would it not be possible to just check what voltage your battery has at 90% SoC and then just set that as the voltage to which it should be charged?

I recall some members in this thread have been discussing the firmware and some seems to have a few versions of it.

I think the problem is rather that the inverter can’t blend power sources. Hooking a battery up to an inverter will always cause the battery to work, it is (in most instances) the power supply of the inverter. However, it seems the Growatts are using the battery to actually provide solar to the loads, indirectly. It should be perfectly fine for the inverter to draw its self consumption (once it is charged) from the battery and invert the excess PV to the loads. It is still using the battery. Otherwise I am sure Victron would put lots of warnings on its “keep batteries charged” option. My personal opinion is that inverters, which can’t blend power sources, should only be used in off-grid situations. It makes no sense to have an inverter, connected to the grid and PV, that needs to power all its loads at any given time from one of the two. It will always underutilise the PV.

Have you considered getting a 48V inverter also? Since you do not have a terribly expensive one currently, it might be worthwhile? Not sure about the downsides of 48V compared to 24V.

Definitely, if you are going to try and start such a massive motor, you have to get more efficient technology if you are going off-grid. Grid-tied, the grid can just start it for you, cheap. The numbers I quoted was explained to me, but I do not have any practical experience with these things myself.

With most pumps though, the running rating is one thing, but starting it is another. It might draw 5-7 times its running wattage for a few seconds starting up. Most inverters can only surge 2 times their kVA. That pump might ask for 112 - 160 kVA starting up (assuming a power factor of 0.8). You will need a small army of inverters. It really doesn't seem like an efficient solution. Even a smaller 10kW pump (let's say 12 kVA) would still ask for 60 - 84 kVA starting. I really think you should rather consider plonkster's suggestion of a dedicated solar pump.

I think @Anish also mentioned before that he is struggling to close to get full capacity out of his Lithiums as his inverter cannot use the BMS data as therefore switches prematurely using only overall battery voltage. I think he has 9.6kWh can use about 6kWh (don't quote me). You'd like to avoid the position where you paid for a 3.5kWh Lithium and can only really use say 2.2kWh, instead of the 2.8kWh you'd get on 80% DoD. However, if you overspecced on the battery capacity, I guess you'd get a long life out of it if you manage it like that, but you should just be aware of that. Obviously the battery's BMS is still only guessing, but it has MUCH more information available to it. All the internal cells' voltages etc.

Keep the Goodwe and Victron stuff in mind also. Goodwe seems to be performing well for many and Victron obviously offers a lot of flexibility. I cannot be happier that I got rid of my Growatt and got a Victron instead.

You don’t need it, but a lithium battery is difficult to manage on voltage, as voltage alone isn’t enough to determine a SoC for the battery. Pylontech would also throttle its charging current when the battery is quite empty or quite full. Most people with a Voltronic inverter seems to go the ICC route to have software sitting in the middle between the inverter and battery to “interpret” the requests from the BMS and relay that to the inverter. Again, this isn’t something I know anything about as I have a hybrid inverter that can communicate with the Pylons without an intermediary. I have heard that in Australia the full warranty on Pylontech batteries don’t apply if it wasn’t used with a proper hybrid inverter (not one marketed as such) not sure about SA.

Hi Lindsay If you are shopping for lithium, it seems to be a good rule of thumb to ensure you get enough battery capacity for your inverter to use in an hour. In your case, the 3.5kWh Pylontechs would meet that requirement. However, they might not like to do it, like the Pylontechs would only give you 100A for a short time, in order to protect itself. I don't know much about the Voltronic inverters, but just be that if you get a lithium, your inverter can properly manage it. Some people do have teething issues trying to run the lithiums on Voltronics without ICC, but personally I have no experience with that.

I did not have it myself. The technician of the supplier I bought from came around when I wasn’t happy with the communication issues between the inverter and batteries they sold me. After I’ve returned mine to the supplier that sold it to me in the first place (technically I guess they sold to my electrician) I had it all replaced with a Victron and Pylontech system. I unfortunately did not keep anything relating to it. I’ve spoken to other installers afterwards who mentioned they found out from the main distributer of Shoto batteries that currently there is no way any inverter would be able to communicate with these batteries. They are working on a solution, but wasn’t clear when it will be ready. I’ll pm the details of the supplier.