jykenmynie

My advice would be to sit down with a good installer, work through your exact back up needs and statistics about the weather in your region. Then you get an idea about the battery bank you are looking for. I’d say that you probably don’t need to go all out on the batteries and just get a generator for the few really bad days in the year. Remember to take into account battery capacity degradation and DC to AC conversion losses when sizing the bank. You don’t want to go just on the rims from the get go, because your capacity might decline in a few years to the point where it doesn’t meet your needs anymore. PV is the cheapest item here, so see how much you can overspec it. Also don’t just go north. Try east and west also for early morning and late afternoon sun. You want to limit your reliance on batteries as much as possible.

Note that not all hybrids have this limit. Victron MP 5kVA can transfer up to 50A and invert another 20A on its outputs. So while Eskom is up, you don’t need to worry about overloading the output of the inverter as you have at a minimum 11.5kW available, and if you have spare PV, up to another 4.5kW (assuming DC to AC conversion loss). This is quite an important feature for me, because I didn’t want to be limited on my essential circuits (which includes all the plugs, even those that would have heaters on in winter) while the grid is available. I think some other hybrids do go up to 40A though, which should be enough.

Obviously Victron’s MP and Quattro inverters are also “hybrid”. Yes, when appliances that are directly connected to the grid requires power, they would create a demand for it, which something like an energy meter reports to the inverter. The hybrid then knows how much power it can essentially send upstream to try and “zero” the energy meter. This is obviously great for fully utilising all the PV you have, but not going through the expensive of purchasing 15kVA worth of inverters to run your entire house through, unless you actually need to be off-grid, then a hybrid won’t help. It does require you to think just a little more about sizing and managing your battery bank, because the inverter would try to zero the energy meter with batteries as well as PV. It would still stop discharging the batteries at a minimum SoC level (unless there is loadshedding, when it’ll take it deeper to keep the critical loads alive). So turning on your oven when there isn’t enough PV would attempt to take the power from the grid, which it will at first, but then the inverter would pick it up from the battery bank. Obviously the inverter still has a hard limit on inverting capacity, so if you have 10kW of PV available and 10kW of demand, and the batteries are full, it’ll still only take 5kW and invert it to AC (getting say 4.5kW AC). The rest would still go to waste. This situation is typically not possible anyways, because the built-in MPPTs of most inverters aren’t big enough. With a Victron though, you can add what you want on the DC side and therefore create “excess” PV if you need it for a cloudy day, for example, because the entire system is modular. Essentially, a true “hybrid” is able to bled power sources and push back to the grid (either only to the rest of your house or beyond, depending on settings). It doesn’t need all its power from one source at a time (like PV only, battery only or grid only) and can utilise excess PV much better. You can run your geysers and washing room from PV during the day, for example, even though they are not on your backup circuit.

I didn't update my firmware, my VRM portal updated itself automatically. All the information was already available, just not displayed as it is now, so nothing changing in the internal workings.

Yes, it is amazing. I always had to open remote console (during the day I care zero about stats, only about instantaneous demand and capacity), now it is all there. The details on the battery can also be shown, so it is perfect. Things I'd also like to see: 1. The looks like the data in the live view isn't updated in real-time, you need to refresh (stuff like the weather, the data in the little blocks) 2. From what I can gather, PV production is shown gross of conversion losses. I'd like an "AC side" production to be shown somewhere. Maybe just below the total consumption block. 3. Also, the total live DC input should be shown (PV + Battery)

So, on a good day, like yesterday, I generated 17kWh on the DC side, from my panels. I have 12*320 = 3,840W worth of mono panels. I had maybe another 1kWh I could've used, as the panels idled a little from 16:00 to 18:00 (and my panels are west facing, so I still have some power then). But I think I am pretty much maxed out on 18kWh. So the investment in my panels was about R60k, MPPTs and installation included. CoCT rates on the electricity used after 600kWh for the month, is R2.53 per kWh. So I calculate my ROI on that since my panels keep me out of that range (it is an overestimate on my ROI, but I use it as a "best case" calculation). Therefore, I can save R45.54 * 90% per day on the AC side, on the best day. So I'll rate that down by 50% (prudently) for bad PV days, but also four out of the three weeks days where I probably won't get to utilise all the available PV. After a year of monitoring my system, I'll have better data to do an actual calculation. That puts me on about R20.5 per day of savings, or R7,485 per year. Again, assuming Eskom increases in line with investment return earn on the R60k outlay elsewhere (prudently), I shall pay back my investment in about 8 years. BUT WAIT! You say. What about the inverter and the batteries? To me, backup power was a luxury purchase that requires to ROI but my convenience in having power. So it is excluded from my calculations. With an inverter and batteries thrown into the mix, my payback period (as I went Victron and spent R22.5k + R4.5k on the inverter and Venus GX as well as about R45k on the batteries) would be much longer than I expect my batteries to last. But that was never part of my justification for the panels or the purchase of backup power to begin with.

You could, but I'd rather not allow for it in my ROI calculations and be pleasantly surprised if they do and my ROI is better than expected (or payback period is shorter than expected). However, as an actuary I am inclined to add prudence in most of my calculations, which seems to be a pragmatic way to deal with uncertainty.

For me, Victron has nothing to do with pride. You are building a system with presumably R60k+ worth of batteries and R30k+ of panels. Maybe another R10k for DBs and a bit of wiring. Now decide what inverter you want. I can go on and on about why I think Victron is an amazing product, with brilliant support, flexibility and reliability. However, I could also say: You probably want to go solar because you are sick and tired of Eskom’s unreliability. In that case, you probably want to replace Eskom with something reliable.

Sorry for the double post, but I’m on my phone so difficult to quote and type stuff in one post. The battery would still register those little discharges and charges as cycles whenever it needs to smooth the availability of the PV. But I did note that batteries are useful up until it makes your solar viable, or you are off-grid (or your backup needs are immense). However, grid-tied, it isn’t financially as beneficial as panels or in fact many over energy saving options.

Oh but I can. As I said, I assumed that Eskom’s increases are on par with the interest you would earn on the money you would have spent on a battery. It is just easier that way. Mathematically you can express it as 12,096kWh x (1.10)^5 (assuming you will use the battery for 10 years, at which point it is out of warranty, so 5 years is the mid point) x (1.10)^-5 (discounting it for 5 years at an annual effectively interest rate of 10%, if you are able to earn 10% return elsewhere) so the 5 doesn’t matter, neither does the 10%. It just gets back to 1 as the adjustment factor. What you should rather ask yourself is, how much can you earn on your investments (probably not 10%) in which case you do gain a bit. However, you’d also need to be confident in Eskom’s future increases and that it’ll keep on being that high, for this calc to tip in favour of the battery. It is also quite likely that you reach 10 years without even reaching 6k cycles, for example, at which point the battery is out of warranty and might just break for a different reason.

Not sure how to R1.3/kWh. Think they rate it for 6000 cycles with 60% capacity remaining at 80% DoD, you can assume linear degradation of capacity for simplicity. And DC to AC conversion has about 10% loss. So: 6,000 * [(1 - 0.6)/2] * 0.8 * 3.5 * (1 - 0.1) = 12,096 kWh usable on the AC side. The battery costs about R23.5k, so R1.94 per kWh. Pretty much in line with CoCT tarrifs. Batteries are only useful up to the point where they make your system viable (the inverter would be able to function normally) or if you are completely off-grid. Unless Eskom increases rates by most than the investment return you would earn elsewhere. If you have spare cash, I think this is more effectively invested in stuff like a heat pump for your geyser (when you don't have solar power it still saves money), LED lights, more energy efficient appliances, etc.

If you look in the "Inverters" section of the forum, there is an extensive thread on Growatt inverters (the SPF5000 series) and it doesn't look like even Pylontech works well with it with maybe there having mixed experiences. This is problematic as the batteries are like double the cost of the inverter for just one... Personally, I won't go the Growatt route if you want to go LiFePO4, not just from my own experience but also judging from those on the forum.

In that case I wouldn't bother with the geyser.

True, but if you plan on moving soon, maybe all of this isn't necessary.

Why would you want to do that? Won’t the generator just work harder then, and you would have all sorts of losses first converting the gen’s AC to DC to charge the batteries and then the batteries’ DC to AC again when you use them?

I hope you find a solution, but if you don’t, my advice would be: It sounds like you’ve invested heavily in batteries and panels as well. It might be worthwhile considering that the cheapest next step is to scrap that inverter and get a good one. I had a Growatt inverter for maybe a day or two before I initiated a return. Not the installer nor technician of the supplier could get it working properly with the battery that they also supplied me. The technician tried to convince me that all my troubles will go away if I just installed panels and not just use it as a backup. I don’t even want to imagine the trouble I was going to have, had I gone ahead and installed panels on the Growatt. If they cannot implement a proper charging and discharging of lithium batteries, why would panels fix that problem? I paid extra, got a Victron, and have been happy since. No worries. Everything just works. Yes, it does cost much more than a Growatt. But it doesn’t cost as much as 3xUS3000B batteries. And also works better, as it is a proper hybrid inverter. I’m extremely glad I came across this forum when I did...

So the Pylontech BMS will allow higher rates of discharge, up to 100A for limited time. I have not tried to push mine, but I only have a 5kVA MP II so it is capped at pulling 100A from both my batteries, so 50 from each. Never had to do that before though. Have seen it get up to 80A perfectly fine for a short amount of time. When we get into Quattro territory, maybe @plonkstercould help out? My pedestrian Multiplus knowledge might not apply. My gut feeling is that the Quattro would be able to invert 10kVA from DC to AC (to probably about 9kVA after losses), so it can attempt to pull 200A from your bank for extended periods, but possibly up to 400A in short bursts. On the warranty, this is something you need to check with your supplier. Not sure who did your installation and supplied the parts but have read on the forum before that some suppliers might not honour warranties on batteries if it wasn’t appropriately specified for the inverter. You will not use less energy to heat up your water with a smaller element, it will just need to run for longer. The temperature you want to get your water to and the temperature it is currently are the only determinants of the energy required. If you normally run the 3kW element for 2 hours you’ll run the 2kW element for 3 hours. I’ve got a 2kW in my 150l geyser, will not suggest going 2kW in 300l unless you don’t mind waiting. Just remember the conversation here is about buying another battery or two to heat his water in the early hours of the day, or getting a heat pump to heat it from his current bank. The heat pump and the batteries have a similar expected lifetime, so we only need to consider which one will cost more over its life. A heat pump plus installation and one battery cost about the same. The heat pump will for 10 years use less than a third of his current energy to heat the water. The battery will only be able to help with half of it if the battery had been fully charged with solar. That would not always be the case. I’m not sure there is any argument to be made for more batteries, unless his bank is currently too small for his inverter’s instantaneous demands.

Okay, I’m talking to my mom this weekend about the maintenance of that piano! Jeez, can’t let an heirloom go to waste. It was the piano on which the four generations since my great grandmother was taught. If I recall correctly it is also a Müller, but I have never tried to trace its origin. I remember that the old blind German tuned that came to house to tune it always wanted to buy it afterwards, doubt he will still want to do that now... Ah, a good way to start my day with positivity! 😅

One US3000B is okay with running at 100A for something like 10 seconds (can’t remember the specs exactly), so your three in parallel can do 300A for a burst. I’d be more concerned with your inverter’s ability to pull up to 20kVA for short periods of time or run at 10kVA for long. Disclaimer: I’m very much a layperson when it comes to the technical aspects of these parts and my observations should be considered in that light. If you haven’t had any issues with the batteries shutting down to protect itself yet, you probably don’t need to worry about it from a troubleshooting perspective. From a warrantee perspective, I’ve heard that it is possible that some suppliers might not honour these if the batteries were under spec for the inverter they were supporting.

I bought myself a Clavinova CVP-401 second hand for about R10k when I started working. Yeah, it doesn't have the same character as an actual upright (not even considering a baby grand, let alone actual grand). However, having moved a lot, the Clavinova is a much better travel partner, no going out of tuning! It has a pretty natural feel due to the weighted keys and a good sound. And then there is the added fun you can have with it - Although I rarely did as I'm pretty much happy with just classic piano music. Recently, I started playing much more up beat stuff... Whatever seems to make my baby daughter happy, more Old McDonald, less Chopin or Debussy! When my mom moves to a smaller place, I'll see if I can convince my siblings that I should get the upright. Really nice, ivory caps on the notes and rose wood inlays (though two caps flew off after a few bouts of glissandos - which also put a to such abusive playstyles). But it needs A LOT of work. My mom hasn't been keeping it tuned or serviced...

Get an installer to do a site inspection. I received a quote for full installation (everything that is required - excluding a geyser of course, I have one) and a 4.7kW ITS heatpump for about R25k. Keep in mind that, while this is close to the price of one battery, it will actually save you more money (and off-grid battery time) than a 3.5kWh battery will. That battery will be empty after an hour of running your 3kW element. Then you won't yet have enough hot water (obviously depending on how much water you use, but you mentioned 2 hours of running). The heatpump would use about: 6kWh / 4.7kW ~= 80 minutes @ 1.17kW ~= 1.5kW. So you just saved 4.5kWh (that is 1.6 US3000B batteries if you discharge them 80%). My above calculation have quite a bit of margin for error in before it is equivalent to one battery only. Also, when the sun isn't shinning, a heatpump would still save you money while your batteries won't be able to be charged properly with the available PV.

So the "rule of thumb" as I have it, is 1kWh per 1kVA your inverter can invert. So 10kWh for you. However, Pylontech's BMS has some more restrictive discharge current allowances. So the way I have it is that for my 5kVA MP II, I should really run 3xUS3000B. So for you, 6 would probably be optimal. I'm not an expert on these items, so I'd rather wait until someone more knowledgeable replies. Agreed, so both of those are "luxury" purchases for me - So if you like it and can afford it - Do it!

What really helped me understand my electricity usage patterns is the energy meter I installed with my backup system. First few days I was running around like a mad-man, monitoring what appliances came on and their usage. Now I can basically just look at the time of day and the instantaneous usage and know exactly what is happening in my house, even when I’m not home. Just with that, I was able to make my wife more energy conscious (I’ve always been very frugal, coming from a farming family where we saved water and electricity like mad) by showing her what it uses and costs (she is very clued up financially, so that wasn’t a difficult conversation). Just using electricity better already helped a lot, such as: - Switching off unneeded lights - Not boiling more water than one needs - Not leaving heaters on or using them when extra clothes would do - Not using the tumble dryer when the sun is out (washing machine is also a biggy if it needs to heat water, similarly dishwasher, but those are less easily optimised) So then we got PV and shifted our loads. Granted, my current setup is west facing so early in the day it isn’t great, but that would be rectified in the medium term, but still we ended up saving 60+% on our purchases from the grid. I can likely improve upon that, but not running my batteries below 60% at the moment. This is just due to my PV being somewhat underspecced, so on a good day, I’ll still struggle to meet my day time demands and bring the batteries up from 20% to 100%. We are in the process of adding more PV that would hopefully help with that. Maybe my story helps you in your quest to save some of those kWhs!

You’ll be hard pressed to have batteries reduce your payback period, unless you strike a lucky deal somewhere. Something like Pylontech US3000B is about R23.5k. You get 6000 cycles at 80% DoD and at that point 60% of the original capacity will remain. Assuming that the degradation is linear, you’ll be able to pull: 6,000x3.5x0.8x0.8 = 13,440kWh from it. At R2 per kWh from Eskom, that is barely the original purchase price. Assuming that Eskom increases are in line with investment return on assets you would invest the R23.5k in. My view: Size the battery bank for your inverter, so you don’t damage the batteries in trying to draw more current from them than they could give. Beyond that, there’s better investments, like a heat pump on your geyser, in my opinion. And it saves you money even when the sun isn’t out and you need to buy electricity from Eskom and can’t generate the PV.

Run it off the grid if you are running it that time. At least that is what I do. Not for it for me to save a few bucks on the one hour of a geyser heating up every day and abusing my batteries like that. I set a scheduled charging slot for my batteries between 05:00 and 07:00 during which time my geyser comes on. The scheduled charge is set to stop at 30% SoC, which is lower than my minimum SoC of 50%, so all that really happens is it prohibits my batteries from being discharged during that morning geyser slot. Or get a heat pump for your geyser. That might be a better investment than another battery and cost about the same.