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jykenmynie

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jykenmynie last won the day on June 22 2020

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  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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)
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. 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.
  13. In that case I wouldn't bother with the geyser.
  14. True, but if you plan on moving soon, maybe all of this isn't necessary.
  15. 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?
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