GreenFields

The question of whether to go with AC-Coupling or DC-Coupling should also consider when you will be needing the power. If you're using the power mostly by day, maybe exporting it, or consuming it instantly as it is generated, then it's probably better to go with a grid-tie inverter on the AC (load) side. If you're going to be storing power in the batteries to use later, then it's probably better to go with an MPPT on the DC (battery) side. The difference is in how many DC-AC and AC-DC conversions you will be doing, ie. efficiency plays a role. But it's also taking into account that the inverter's rated capacity is likely to be the bottleneck in your system.

Two main concerns. First is is to understand the total energy requirements better regarding generation and storage ie. when does the Kilawatt show your current heating of 11kWh is taking place, day and/or night, and will the system be able to generate and store enough total energy you need, in whatever size geyser size you have on hand, to cover evening and morning hot water needs. Worst case if you've got say a 150l geyser and it gets heated up effectively for 1.5-2 hrs during the day, then emptied in the evening, and re-filled cold, and heated for another 1.5-2 hrs during the evening, you should check whether daytime-only heating is going to produce the real-world savings you're looking for. Second concern, is why you are looking to use an unapproved panel configuration. Just reading through the Elon manual, it's quite extensive in its listing of recommended/prohibited/sub-optimal panel arrangements, and says that any alternative setups should be checked with them. My concern is, even if it works technically, that they may not support warranty claims on panels that they didn't agree to. Also, just looking through the manual regarding energy requirements for various cities, it seems you'd be better off in Durban to go with around 3kW of panels, probably in a parallel configuration as per the manual. Side-comment: Having 3kW of the same panels once-off is also "safer" to upgrade with, ie. to transfer to one MPPT of a 5-6kW inverter later, without having to mix and match panels. I understand that financing is a constraint, and I love the idea of not paying a premium, but I also hate waste and risk.

I saw that comment, which is fair enough of what's been happening locally in the past. But I'd guess that the new local rep of a battery manufacturer could have access to international recycling facilities, if they can gather up enough of the local stock through a buyback programme to make exporting it worthwhile. Not saying this is what they are doing, but I think the business model could be workable, considering that they are also selling new product in its place.

Okay, so then the R2K on offer (approx $120 USD) is about middle of the road or average for the reported international scrap value of the battery. Just stating the obvious. I'm sure the newer batteries are better and more desirable, but each one must maar decide for himself how much his old generation battery is still worth to him.

Out of interest I just did a Google search using the words: "48v 75ah lithium battery raw material value in us$" and got the AI answer: "The raw material value for a 48V 75Ah (approx. 3.6 kWh) lithium iron phosphate (LFP) battery is roughly $220 to $300 USD, based on average cell-level LFP raw material and commodity benchmarks" I make allowance that this may be inaccurate, but for sure I'd want to dig deeper before thinking even for a second of selling some fully functional built up batteries for possibly half the cost of the materials used to make it. Don't care, not leaping before looking.

Some other stats worth noting. Maximum Open Circuit Voltage is 500V - never exceed this value. Other thing is that the battery charge spec is a maximum continuous charge of 100A, but a recommended charge of 40A (0.2C), while the solar charger can handle 200A. The BMS seems to allow 200A surge discharge for 16 seconds if I'm reading right (subject to correction). I suppose it is what it is and it does what it says on the box, but I'd have liked a higher continuous battery charge/discharge rate to support the rated 10kW for longer in the absence of the sun, if this is being sold as an all-in-one 10kW solution. In any case, I think you could re-evaluate if you need the full 10kW of panels with 200A charge capability, if the battery can't handle it. Personally I'd install just 5.5kW at first, say 2.75kW per PV input, or say 5x550W panels per PV input, and then later evaluate if you want more. Depends on the rest of your daytime loads.

For surviving on minimal power, a 400W wall panel heater per room, then close interleading doors and only heat the rooms you need. Or electric blankets.

The Smart load uses a separate port. Please confirm, or check whether the geyser is connected to the "GEN" port on the underside of the inverter. It might be that it's just connected as a non-essential load, ie. on the Main switch as a household load, but excluded from the backed up home circuits on the LOAD port.

Please confirm your inverter model, and the type of grid supply or wiring layout. I can't find any info on an 8kW 3-phase Sunsynk inverter (assuming you meant kW not kWh). Or are you saying that you have 2x single-phase inverters, each connected on one phase within a 3-phase power network? What phase(s) are your loads on, and which are the inverters on?

This issue cannot be resolved with a connection or a setting. It is a characteristic of the panel that is not optimal for the inverter's charger type. Also, considering that the house is already facing around 20 degrees East, those panels are actually facing a bit towards South-East, further reducing the generation capacity. Would there be too many shadows if you fit them to the main roof facing North-East? Unfortunately you've got a complex situation with possibly no easy solutions.

Layman's 2c, use at own risk, or get advice. Some points to consider all the same. You've got an inverter with a 1200W PWM charge controller. In Winter that's just not quite enough to keep the battery charged. On average, touch and go, under the best of conditions in Winter, it's just-just sort of okay, but most of the time not, and if you're intending to run daytime loads from it as well, then you just don't have enough power generation capability. On top of that your setup is likely not optimal to begin with. I'm assuming that your 2 x panels are connected in parallel, or it would have exceeded the inverter's max VOC and caused a failure. If this is not already in parallel, you really should change it over to parallel. But your panel's Vmp isn't ideally matched to the inverter. Better would have been to use a panel like the Canadian Solar HiKU6 CS6W405MS panel (x3), because the Vmp spec is better aligned with the battery charging Voltage. Unfortunately you've got a 25% loss of efficiency with the current panel right out the gate. You could lower the discharge cut-off Voltage to 20V (spec as per the battery), ie. discharge it deeper than the inverter is doing now. And then I think you should change from SBU mode to utility mode, ie. just keep the battery and panels on-hand as a loadshedding solution, without trying to power the whole house from it permanently. You'd have to do a more drastic upgrade, like changing to a 24V MPPT-controlled inverter, and adding maybe another two panels, before you can start thinking of running daytime base load and then still charging the battery by day for draining at night.

Given the East/West split, you won't see the full 7.7kWp anyway, the peak should be lowered to around 7kW at mid-day in high summer (you can check it on an online solar calculator). Maybe calculate by another route and compare it to your current mid-day peak in summer, then add another 17% on-top of that. I'm not in a position to give a comment on the safety.

Winter solstice was just 3 days ago, so ja, poor power generation is still basically the worst right now that it will be all year. But the 1000W on a panel set of 4360W sounds like too little. What's the Voltage and Current on PV2? Around 250V and 4A? Do you generate any more on PV2 if the PV1 string is disconnected? Do you have any problems with shade being cast over that 2nd string?

Doesn't sound immediately like an issue, just the info communicated by the batteries (BMS) to the inverter. Sounds like 3x105A discharge rate, ie. 105A discharge spec per battery.And the charge rate may vary depending on how fully charged the batteries are. But in any case if you have just the one inverter you'd have a peak charge rate from grid of around 120A-150A give or take, just guesstimating. And around 110A from panels. So you'll basically never put stress on the batteries. Money wasted unless there is a clear sign of a fault.

You could check whether a 24V Victron Multiplus setup would work for you, but in the long run it's a strong consideration to transition to 48V or even HV batteries, if you want to increase the system power. What exact batteries have you got, and what's the spec for lifespan or number of cycles ? That might also help guide the level of expense to incur now for the 24V path. Maybe you could look at options for the best use-case, if you would dedicate this 24V / 3.5kW / 20kWh system to a feed a specific 15A sub-circuit in the house, and get a different 48V inverter system to feed the main circuit breaker. Similar to how you have an MPPT dedicated to a geyser. Meaning, maybe use this exclusively for running an aircon, or a pool pump, or get an electric vehicle.