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Axpert 3 kva vs 5 kva


PaulF007
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Good evening 

After spending some odd two weeks of reading through the masses of info here I am almost ready to jump info the off grid world. My inisial planning was to go with the Axpert 5kva but due to budget constraints I am considering the 3 kva Plus - 24v will lower my initial capital outlay.

Some questions with regards to this:

1) I understand that I will have 2kva less power to work with and will most likely be able to compensate through sequential usage but I went through the speck sheet and it seems like I will only be able to draw 1.5kw from my panels is that correct?

2) As my Cash flow gets better what would be better 1 - to increase my storage capacity 2 - Increase the PV panels or 3 a bit of both ( I see that the Chager can handel up to 60 A) 

3) Will I be able to add another 3kva unit in parallel and will this then dubble the charging capacity?    

I though I had it all figured out but after a quick chat with TTT made reconsider my thinking - BTW thank for the info TTT !! 

I hope this all make sense!

 

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Hi DB 

It is going to be a off grid system and will only move in after everything is running. I have started to make the necessary adjustments for peak usage and will most likely need to make some sacrifices in the short term. I also have a 5kva Diesel generator that I will use on high loads - IE if the miss would like to do some baking. So I will have to upgrade in the future. 

Hope this answers you question.

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We will manage the high usage during daylight time so that we dont need tap into the batteries and will keep usage to a minimum at night. Mostly TV freezers and lights , will do most cooking on gas strove and will use the micowave (1500 w) but will be 5 min max , the wife sterilize the baby's bottles and some food heating up for a min or two at times.

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1 hour ago, PaulF007 said:

BTW thank for the info TTT !! 

That is what we are here for.

Paul, maybe an idea, and now I am really going on on a limb here, a 24v Multiplus with smaller generator, using the assist function to combine batts and gennie at night for when the missus wants to bake you some pie. 

Guys, before you all jump down my throat, I am not pushing specific product here, but in recent chats here on the forum, where gennies come into play with off-grid, you may not have to go all the way with 48v large inverter stock standard approach if you have to have a gennie that can carry the larger loads temporarily. 

With a biodesel generator ... ok ok ok ... lets not go there yet.

@plonkster would you mind weighing in here?

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It was a thought but read some where that a genny might give problems with the HTZ that does not come in sync with the inverter - specially if you use the one cylinder engines. The article was very technical  but it came donw to only having one power stroke makes it hard for most gennies to keep up. But that was just some reading , no personal experience.

 

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42 minutes ago, The Terrible Triplett said:

Guys, before you all jump down my throat, I am not pushing specific product here, but in recent chats here on the forum, where gennies come into play with off-grid, you may not have to go all the way with 48v large inverter stock standard approach if you have to have a gennie that can carry the larger loads temporarily. 

Sure not ;)
Now going this route you still need to add a SCC putting you beyond the costs of what a 48V Axpert system would cost (Sure you could add the batts and it would still work out cheaper than the blue setup on 24v).

For the gennie just add a change over switch for when you need it and bypass the complete inverter setup since it won't be for long runs.

Now something that I have been thinking about maybe @plonkster can help with the logic of this.
If I set the Axpert to allow grid/gennie charging of the bank, wont this kind of act like "PowerAssist"

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Hi Paul I run an off - grid system and there are pros and cons for both.

3 kVA

Pros

  1. Cost of the unit (marginal R 2-3K).
  2. Can have 24V battery bank (depending on size could be a considerable saving).
  3. Low quiescent current ~ 20W as opposed to the 4kW which has a quiesecent current of 40-50W.
  4. Friend's 3kVA system ran perfectly on my Chinese no-name gennie.

Cons

  1. 3kVA limited capacity. (I thought a 4kW system would be adequate and it is but on occasions 5-6 kW would be nice. - Seems the the more you have the more you want).
  2. If the battery bank is a 24V system then each individual battery has to work twice as hard to supply a set 2kW load as compared to a 48V system.
  3. Limited to a nominal 1500W solar array . You can oversize one's array but the recommendation is for this to be by only 30 - 40%.

5kVA

Pros

  1. 4kW  I can bake bread, weld and do other serious sh#t if I want to (and I do).
  2. 3000W solar array - I can run some heavy loads direct off the panels and not discharge the batteries in fact on a good day I can heat a geyser and charge batteries  at the same time. This array can also be oversized.
  3. If you think that you can get by with a 3kVA you probably will not need to upgrade a 5kVA.

Cons

A more expensive 48V DC battery bank.

 

I will check tomorrow if my Chinese gennie works with my 5kVA and report back.

If the size of your battery bank is determined by required backup capacity rather than budget then the 48V battery bank beats the 24V battery bank. A 24V 200Ah battery bank is ½ the size of a 48V 200Ah battery bank.

 

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48 minutes ago, Chris Hobson said:

Seems the the more you have the more you want.

Well said Chris.

Although it is a perfectly normal human reaction, striving for more and better, the sweet spot is where you can balance the costs with comfort, even if you have to suffer a 21st century inconvenience here and there ... which widely differs between us all.

I found that once you realise you can go smaller, living with resultant small sacrifices, the reduction in capital outlay can be substantial.

But, for each of us, to find that sweet spot, not an easy or simple thing to do at all.

 

Side Note:
It will by a completely solid frozen Cape Town the day I will be limited ito size of a solar array. I will spend the monies to keep the charge controller separate from inverters and add as many panel as I want when I want on as many controllers as I want - 21st century luxury for me. :D

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16 minutes ago, Chris Hobson said:

Hi Paul I run an off - grid system and there are pros and cons for both.

3 kVA

Pros

  1. Cost of the unit (marginal R 2-3K).
  2. Can have 24V battery bank (depending on size could be a considerable saving).
  3. Low quiescent current ~ 20W as opposed to the 4kW which has a quiesecent current of 40-50W.
  4. Friend's 3kVA system ran perfectly on my Chinese no-name gennie.

Cons

  1. 3kVA limited capacity. (I thought a 4kW system would be adequate and it is but on occasions 5-6 kW would be nice. - Seems the the more you have the more you want).
  2. If the battery bank is a 24V system then each individual battery has to work twice as hard to supply a set 2kW load as compared to a 48V system.
  3. Limited to a nominal 1500W solar array . You can oversize one's array but the recommendation is for this to be by only 30 - 40%.

5kVA

Pros

  1. 4kW  I can bake bread, weld and do other serious sh#t if I want to (and I do).
  2. 3000W solar array - I can run some heavy loads direct off the panels and not discharge the batteries in fact on a good day I can heat a geyser and charge batteries  at the same time. This array can also be oversized.
  3. If you think that you can get by with a 3kVA you probably will not need to upgrade a 5kVA.

Cons

A more expensive 48V DC battery bank.

 

I will check tomorrow if my Chinese gennie works with my 5kVA and report back.

If the size of your battery bank is determined by required backup capacity rather thasn budget then the 48V battery bank beats the 24V battery bank. A 24V 200Ah battery bank is ½ the size of a 48V 200Ah battery bank.

 

Hello Chris

Thank you for the info I was wondering about that the 48v vs 24v batt capacity my logic was 200Ah 24v = 4800w vs 200 @ 48 = 9600 stands to reason that I could get Half the batteries and sacrifice the luxury for now and add another pack later.(Can still use the genny for now) 

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15 minutes ago, PaulF007 said:

Hello Chris

Thank you for the info I was wondering about that the 48v vs 24v batt capacity my logic was 200Ah 24v = 4800w vs 200 @ 48 = 9600 stands to reason that I could get Half the batteries and sacrifice the luxury for now and add another pack later.(Can still use the genny for now) 

Adding another parallel battery bank later is not recommended unless the 1st is less than 6 months old.

Edit
Also remember when you upgrade later on you can't/not recommended add another set of 24v to the old 24v set of batteries to make up a new 48v bank if you maybe decide to upgrade to a 48v inverter.

Then the other upgrade path on paralleling two 3kva 24v inverters will also limit you to the first 24v bank as the inverters share the same bank

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7 minutes ago, viper_za said:

Adding another parallel battery bank later is not recommended unless the 1st is less than 6 months old.

Edit
Also remember when you upgrade later on you can't/not recommended add another set of 24v to the old 24v set of batteries to make up a new 48v bank if you maybe decide to upgrade to a 48v inverter.

Then the other upgrade path on paralleling two 3kva 24v inverters will also limit you to the first 24v bank as the inverters share the same bank

Will I be able to add another 48v bank parallel if it is within 6mnts? Assuming that I go for the 48v system

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I have  a 48V 260Ah battery bank and I would say for off-grid 400-600Ah would be a good balance between cost and practicality. Fortunately I can move these batteries to a second system if there is still some life in them when I upgrade. My battery bank size was entirely budget determined and it is too small.  

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Chances of getting it right the first time around, having never used solar before, is near naught. Either you over or under spec the system, only time will tell you.

You have to "feel" that first premature battery replacement, that inverter that failure outside warranty or due to a moment of "Ag my liewe &#@!!!".

So guessing here, based on own experiences to date:
1st time round - last about 1-2 years, learning curve very steep, SWAMBO and you are eyeing each other, war is imminent.
2nd time round, getting quite wise and less tolerant you get it near spot on - years 3-10, SWAMBO and kie are under control, most of the time.
3rd time round is just replacing failed parts - years 11-25 for panels are done so you do it right onetime - SWAMBO tells everyone what a cool system SHE has. :D

It is a journey, it is going to cost, SWAMBO is going to shout a few times at you. 

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I am going to put here what I told Paul.

He said evenings, and I quote:
 - Have started to make the necessary adjustments for peak usage - where it all starts - reduce the load and peaks.
 - Will most likely need to make some sacrifices in the short term - fully aware of the facts.
- Also have a 5kva diesel generator that I will use on high loads - IE if the miss would like to do bake - could there still be a flywheel concern?
- Will manage the high usage during daylight time - not necessary on sunny days, cloudy rainy days being off-grid, generator is there.
- Will keep usage to a minimum at night. Mostly TV freezers and lights - Assuming fridge is inverter based A+ or A++, LED Tv and LED lights, it is a low load compared.
Will do most cooking on gas strove - Sorts that load quite nicely.
And will use the microwave (1500 w) but will be 5 min max - so 3000va is spot on for microwave and all the other loads mentioned, on simultaneously.

Batteries - 4 x 6v Trojan L16RE-B 370ah 24v bank to deal with Chris'es worries, which are very valid.
If not Axpert, using separate CC that can handle the daily load and re-charge the batteries, you can add more panels  / controllers as and when you need more power daytime.

What have I missed?

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9 hours ago, The Terrible Triplett said:

- Also have a 5kva diesel generator that I will use on high loads - IE if the miss would like to do bake - could there still be a flywheel concern?

Diesel generators even the cheaper ones tend to be well made. Since they operate at much higher pressures (except the slow speed Listers whose compression could be compared to an old age home fart) they all have a decent flywheel - part of the necessary design to get them over the hump. Field Marshall tractors that had a single two stroke engine that could run backwards if the engine laboured going up a hill and the flywheel did not have the momentum. The engine then mis-fired and because it was now able to roll back it would fire on the next stroke but run in reverse. A bit disconcerting especially if you were towing a trailer-load of lucerne.. . 

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14 hours ago, The Terrible Triplett said:

 would you mind weighing in here?

Been somewhat off-grid, down and out with the flu and I've been pushing hard on a little Rpi project when the drugs are working.

If you have a good Diesel Generator, the low RPM kind with a nice stable waveform, the inverter will tie with it. The idea is to run a smaller generator at >80% capacity and make up the difference from batteries/solar. For this you need a real hybrid inverter, so the Axpert won't work. While most GTIs should work (I know people who tie their Schneiders with a Diesel generator), this really isn't what you want to do, because as Chris said, an unladen Diesel engine makes some of the most expensive electricity. What you want specifically is what Victron calls PowerAssist, where a fixed amount is taken from the generator, and the difference comes from the battery.

So I would think a 5KVA Multiplus combined with a 5KVA generator ought to do the trick. You can then pull up to 10KVA if you wanted to, but most of the day you run straight off the solar/batteries because you're under 5KVA. This is exactly the scenario in the whitepaper I linked previously, where they cut their Diesel consumption in half by adding the inverter.

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2 hours ago, plonkster said:

5KVA Multiplus

Paul is a off-grid setup, so no GTI possible. I am now asking for myself, with the load mentioned above and having a diesel generator, where will a 24v 3000va Multiplus fall short?

 

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4 hours ago, viper_za said:

What is the price of 4 of these vs 8 x T105RE batts

Roughly:
8 x T105RE's 225ah connected series - 48v 225ah bank = R 21 221.36 incl VAT.
8 x L16RE-B 370ah connected in series - 48v 370ah bank = R 38 664.32 incl Vat.

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16 minutes ago, The Terrible Triplett said:

Roughly:
8 x T105RE's 225ah connected series - 48v 225ah bank = R 21 221.36 incl VAT.
8 x L16RE-B 370ah connected in series - 48v 370ah bank = R 38 664.32 incl Vat.

so taking your example
24v 4x L16RE-B 370ah = 4 x 4833.04 = R 19 332.16 (8 880 watt hours)
48 x8 T105RE 225ah = R21 221.36 (10 800 watt hours)
Going 48v looks like the better bet to me for 2k more on the batts and another 2k more on the Axpert 5kva 48v inverter ;)

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I am sold!!! You win Viper, no jokes. Missed that one totally. Respect.

But before we all run off, being off-grid, within a budget, new to solar has anyone done an analysis of the load to see if the ah of the bank is too much, too little, spot on, best value for money? Are we going 20% DOD or 50% DOD seeing it is off-grid and if needed at times, generator most definitely in the picture with the potential issues of inverter and gennie?

Anyone checked that the panels are sufficient to charge the bank daytime, with enough spare to run daytime loads? And in winter on cloudy days, off grid?

Can maybe a 225ah bank do the job, with careful adjustment of lifestyle, due to diesel generator to auto start and switch off, to stay within a good budget for system 1 to learn or at best, do it once and be happy? Far as I picked up, it is 5-10 minutes of microwave at night, lights, TV, all very small loads.

And we have not said a word about a BMV, battery balancing and software to ensure optimal battery use. Software to start and stop gennie based on SOC.

And I see Plonkster replied and no one said a word:

3 hours ago, plonkster said:

If you have a good Diesel Generator, the low RPM kind with a nice stable waveform, the inverter will tie with it. The idea is to run a smaller generator at >80% capacity and make up the difference from batteries/solar. For this you need a real hybrid inverter, so the Axpert won't work.

What you want specifically is what Victron calls PowerAssist, where a fixed amount is taken from the generator, and the difference comes from the battery.

 

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I assume that it does not help having a discussion off forum so for the sake of someone else reading through all of this. TTT and I had a few mails back and froth and came to the "same" conclusion: (He will still claim that going for the Victron is better :P)

Phase One: Get the Axpert cut on the batteries for now to fit the Budget - then check your usage for the first few weeks and " pas jou Batteries op" for they are ***** expensive.

Phase Two : Increase your Batteries and PV Panels to be a better fit for your needs

Phase Three : Switch the inverter to optimize your system and batteries and allow for better peak usage with the genny and helping with the batteries.

Make the Axpert available for the next person that will be starting with solar , hey we might even have a flouting inverter around the members for "training" purposes.

I shall soon find out whether all my theories are correct ...

regards   

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