Very nice!
Since it has been in operation for two years, can you comment on how your system is doing?
The system is performing very well. The inverters have been very reliable (not a single problem), as has the battery and solar panels.
I do have some experiences with the battery I'd like to share, though...
The first issue is because I am using a battery designed primarily for telco's, access to firmware updates is terrible. I have to use a lot of back doors to get information on this, but to be fair, even without a battery firmware update in nearly 3 years, it just keeps going.
The second issue on the battery is the interface between the BMS and the inverter. Polarium have two interfaces for this. The older one is called the IC-B (Incell Connect Bridge), and the current one is called the SII (SMA Inverter Interface). I had massive problems with the SII where the contactor gets extremely hot (even though it's rated for 500A), and fries the unit.
With the SII, you cannot link the battery to an SMA inverter if you don't have one, as it provides both electrical and electronic connectivity between the battery and the inverter. The IC-B is just pure electronics, translating the battery's BMS data into information SMA can understand. With the IC-B, you use an external fuse, which is a more reliable system.
The default shipping code on the IC-B allows you to only have 60 seconds worth of Bluetooth access to the battery's BMS. When I asked Polarium about this, they could not understand why anyone would want to monitor the battery for more than 60 seconds. At any rate, they agreed to fix it with a code update of the IC-B, so now it is possible to view the BMS data for as long as you want.
They promised to go back and review the design of the SII. That was back in 2020. To be honest, I don't really care. The IC-B and a regular fuse is just so reliable, I'd rather not change it for what, at the time, was unproven tech.
The third issue with the Polarium battery is that it does not come with a pre-charge resistor built in. So I had to construct my own resistor which I wired permanently across the fuse terminals. That way, if I ever needed to switch off the inverter, I can use that resistor to pre-charge its capacitors in order to turn it back on without tripping the battery.
The other thing I have had to manage is heat in the garage where I have them installed, and I used fans for that. But I just added an extractor to help force warm air out, and that has lowered the space's temperature by another 5 degrees-C. I did consider using inverter-based air conditioning units which would draw less than 700W of power, but the costs did not make sense... and cheaper air conditioners use way more power, in the 1.5kW - 2kW range.
Has the 12kW of PV been able to produce what you need in Jan-March when I understand fog/cloudy weather can be common in Johannesburg?
While October - March tends to be our summer period in Johannesburg, where we see the most rain (especially, as you say, between January - March), it is still the best period for solar yield throughout the year. We are blessed with clear-sky winters, and the lower ambient temperatures are great for solar panel and inverter efficiency, but with the sun being so low in the sky, the actual sun hours from which you can make power are far fewer. So even though our summers are rainy, it's still the best time of year to make power. Not so much in Cape Town, as their winters are generally stormy most of the season. And Durban is too far east to have any real solar irradiation compared to the western parts of the country. Johannesburg is not a tropical region, so our rainy summers are not a huge issue as, say, South East Asia.
For a year I had a 38kWh battery pack paired with 7kW of PV and found the battery was too small.
38kWh of battery is a lot of power. Do you mean it was too small in terms of the amount of energy you would make per day from solar so you can have somewhere to dump it, or in terms of your use requirements?
Wondering if your 12kW PV charges up the batteries to 100% early each day, with lots of spare PV available?
It does do, I haven't had any trouble with that at all. Between charging the battery and running the home, I make about 40kWh of solar energy per day.
I do have one issue where the battery will not charge beyond 53.1V, and it claims that to be 100% SoC, with a cell voltage of 3.55V. I have spoken to SMA and Polarium about this, and it seems that the issue is the BMS having firmware that backs charging off at 53.1V. The battery is designed to call 100% SoC at 54.75V, so I'm working with them to get a firmware update so we can unlock that.
If you did it all over again today, with the knowledge you have gained operating the system for two years, would you design anything differently ?
Well, I would use larger solar panels now; in the 580W - 675W range, so as to maximize early-morning, late-evening and cloudy-day solar yield. I would also find some space to have either an east- or west-facing string, to catch sunrise or sunset.
I would use a more commonly-sold battery (EG4, BYD, Dyness, Renogy, Ark Battery, e.t.c.), because even though Polarium's batteries perform excellently, they are not really a retail vendor (their customer base tends to be telco's or large industry). So getting access to them for support on technical questions is a real minefield. It would have ended in tears if their product was not solid, and I was unable to reach them at the same time. These more common batteries also ship with built-in pre-charge resistors, so that would be useful (to be fair, I don't know whether Polarium now support pre-charge resistors in their latest batteries, but I have asked the question... let's see how long they take to respond).
Other than that, I'd still choose SMA for the inverters. There are two things I like from Victron that SMA don't do, which is in-built grid voltage sensing, as well as in-built Earth-Neutral Bonding. But even if I've had to do these two things externally with SMA, I would still choose SMA over Victron. Low Frequency inverters don't excite me
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And I would definitely maintain discrete inverters still, i.e., PV inverter + battery inverter as separate systems. I'm not particularly sold on all-in-one hybrid inverters, unless the application is very very small. And anyway, I prefer AC-coupled systems.
Thanks for your feedback, and questions. Most appreciated!