Inverter selection - 24V system

[JohnBrother]

Hi,
My design is as follows.
4 x 460W panels in 2S2P configuration, 2 panels in series facing South East and 2 panels in series facing South West - I reckon this is going to help to even out the generation. I don't think like 45 degree but maybe 30 degree or even less.

1840W
98Voc in 2S2P configuration, 147Voc in 3S2P (future) configuration.
I want to leave some room for growth to add 2 more 460W panels so 3s2p.
For that I decided to go for Victron MPPT 150/100 battery charger.

My estimated energy usage is 4800Wh (24x 200W) at home. The purpose is to power on 1 laptop, 1 PC, lights, network equipment (router, a switch) with a microwave for couple of minutes. I could experiment with larger appliances like a washing machine and fridge but only when the batteries are full and the sky is clear.
I get about 560Ah worth of batteries. 2x (2x 280Ah 12V batteries in series for 24V) then these two in parallel to get 560Ah.

I was able to find a suitable MPPT with room for growth but I cannot find an inverter that can cover up to 3000W when I add 2 more panels (2760W).
I don't think I would ever need to go over 3000W. I cannot find anything from Victron or it is crazy expensive or a 48V system.

When I look at it I am a bit confused what is the difference between so called power inverters, battery inverters, off-grid inverters.
How I understand it I should go for a battery inverter.
There are also these hybrid inverter+MPPT combo boxes.
Ideally with an uninterruptible switching from PV back to grid but Victron Energy MultiPlus-II 24V 3000VA 70A 32A is pretty expensive so a plain transfer switch in case of a failure or a maintenance would do (for now).

I think before the upgrade I could do with Giandel 2000W 24V inverter.
What would you recommend?

 

[JohnBrother]

I have come across Growatt SPF 3000TL LVM-24P units.
MPP Solar inverters are not available in UK.
Otherwise I have to resort to 2x1500 or 2x2000W inverters but then I need two cheaper MPPTs.
This would still be cheaper than expensive 2500W inverter.

 

[E. Cho]

I would would look for a LOW FREQUENCY Pure Sine Wave INVERTER like a used, "old" Trace or Xantrex SW4024 (4,000 watts nominal and which handle much higher Surge loads than cheaper modern high frequency inverters). The newer versions are called Schneider or Context? These older Trace or Xantex are near bullet proof and provide good clean power. Their only downside in my 15 years is that if the inverter is turned off, then all the input settings are lost and need to be input again on restart. That doesn't happen very often for maintenance, but when it does, until I wrote them all down, that along with remembering the combo of navigation buttons to push for changing or inputting settings was a PITA. But you may find one for a good price and they are very very good inverter/chargers (will charge from a generator or even the grid).

Next might be newer but still a Low Frequency Pure Sine Wave Samlex brand, which if you do a search here for other recent inverter threads, are highly regarded but being newer may cost more than an old Trace?

If it were me, I would stay far away from what I consider to be inverter garbage or toys, being high frequency inverters, they don't always run loads that are needed and you usually don't find out until you need that load, as the inverter manufacturers are less than honest or forthcoming about their capabilities. This includes all the inverters that you mentioned already.

Basically, you want a pure sine wave low frequency inverter, with our without a built in battery charger, with or without grid connection capability, with or without AC input and charging such as from a separate fossil fuel generator (inverter generator preferably or an older diesel generator with a clean Power Factor alternator, mine is a Kubota) for the days of low solar, all at the wattage you require. A good low frequency inverter should last decades. High Frequency modern inverters not as likely.

Don't worry so much about the other inverter labels, many seem to be for folks that want to be connected to the grid too. But do pay attention and ask if it is a high or low frequency inverter and if you want it connected to the grid as a back up, if it can do that. Also ask and insist on a complete list of the type of appliances, motors, or "loads" that any inverter can handle. The modern and hybrid inverters may be a mixed bag and you can read threads here where some folks have trouble with them running a vacuum cleaner, or a microwave or a air compressor or a water pump. My old Traces runs them all.

 

[timselectric]

You need to go about this differently.
First you need to size your inverter for your loads.
Then size the battery for non sunny use.
Then size your solar for the loads plus re charging the battery.
Also, if you are using batteries that have BMS's. You should buy the correct voltage batteries. Instead of putting multiple batteries in series.
That's just my two cents worth of suggestions.

 

[JohnBrother]

I would would look for a LOW FREQUENCY Pure Sine Wave INVERTER like a used, "old" Trace or Xantrex SW4024 (4,000 watts nominal and which handle much higher Surge loads than cheaper modern high frequency inverters). The newer versions are called Schneider or Context? These older Trace or Xantex are near bullet proof and provide good clean power. Their only downside in my 15 years is that if the inverter is turned off, then all the input settings are lost and need to be input again on restart. That doesn't happen very often for maintenance, but when it does, until I wrote them all down, that along with remembering the combo of navigation buttons to push for changing or inputting settings was a PITA. But you may find one for a good price and they are very very good inverter/chargers (will charge from a generator or even the grid).

Next might be newer but still a Low Frequency Pure Sine Wave Samlex brand, which if you do a search here for other recent inverter threads, are highly regarded but being newer may cost more than an old Trace?

If it were me, I would stay far away from what I consider to be inverter garbage or toys, being high frequency inverters, they don't always run loads that are needed and you usually don't find out until you need that load, as the inverter manufacturers are less than honest or forthcoming about their capabilities. This includes all the inverters that you mentioned already.

Basically, you want a pure sine wave low frequency inverter, with our without a built in battery charger, with or without grid connection capability, with or without AC input and charging such as from a separate fossil fuel generator (inverter generator preferably or an older diesel generator with a clean Power Factor alternator, mine is a Kubota) for the days of low solar, all at the wattage you require. A good low frequency inverter should last decades. High Frequency modern inverters not as likely.

Don't worry so much about the other inverter labels, many seem to be for folks that want to be connected to the grid too. But do pay attention and ask if it is a high or low frequency inverter and if you want it connected to the grid as a back up, if it can do that. Also ask and insist on a complete list of the type of appliances, motors, or "loads" that any inverter can handle. The modern and hybrid inverters may be a mixed bag and you can read threads here where some folks have trouble with them running a vacuum cleaner, or a microwave or a air compressor or a water pump. My old Traces runs them all.

Thank you, I will definitely lookup for these models/makers.

 

[JohnBrother]

You need to go about this differently.
First you need to size your inverter for your loads.
Then size the battery for non sunny use.
Then size your solar for the loads plus re charging the battery.
Also, if you are using batteries that have BMS's. You should buy the correct voltage batteries. Instead of putting multiple batteries in series.
That's just my two cents worth of suggestions.

I start with a very basic hybrid system when I hit low solar production and baterries are depleted I simply switch from PV to grid using a transfer switch.
I calculated the the power demand for half of the house - a laptop, a computer and a microwave.
I reckon for a washing machine, fridge permanently connected I would need 6kW 48V system probably 8 or 10x 460W panels.
I would probably build a separate 3kW 24V system for that or make a move to 48V and expand it and decommission the old 24V system.

I calculated the energy demand to be about 200Watts on average but nothing particularly spiky except a microwave for 2min 30sec.
This is about 5000Wha divided by the amount of sunny hours per day on average in my area 3.9h = 1300 Watt would charge it withing 4h.

I reckon LiFePo batteries optimal range of operation is 20-80%, what I red charging over 80% is not healthy for them.
So 8x 3.2V 280Ah cells = 24x 280Ah battery - 40% = 168Ah that can be used daily.
I would make 2 of these 280Ah batteries = 336Ah
I think this would give me only 1 day of backup. If insufficient then I would switch to the grid and in the meantime plan to add 2x 460 panels and a 3rd battery.

They all would be made from the same batch of 3.2V cells so I would order 24 or 32 of them. I understand each one of them would have to have a separate BMS so 3 or 4 BMS modules.
I mean 200Ah 24V battery would cost me a £1000 so £2000 just to meet the requirement.

 

[MichaelK]

I can see a couple of problems here. First,

98Voc in 2S2P configuration, 147Voc in 3S2P (future) configuration.
I want to leave some room for growth to add 2 more 460W panels so 3s2p.
For that I decided to go for Victron MPPT 150/100 battery charger.

Your Victron has a voltage limit of 150V. If you wire three panels in series, the Voc will be 147 ONLY at room temperature. How cold do your winter lows get? Below freezing? You need to multiply the Voc by a correction factor (cf) for cold weather. Right at freezing, a panel string that is 147Voc at room temperature (77F) will be 147V X 1.12cf= 165Voc. If you really want to accurately predict what the voltage of your string will be at your location's winter low, use Midnight's string calculator. https://www.midnitesolar.com/sizingTool/index.php

What does this statement mean? I was able to find a suitable MPPT with room for growth but I cannot find an inverter that can cover up to 3000W when I add 2 more panels (2760W). A component inverter's function is independent of the number of panel watts. It is the charge controller that has to be sized to the number of panel watts, not the inverter. In terms of scaling for your inverter, I recommend you use the 2X rule for sizing. That means if you expect to run a 2000W load, then get at least a 4000W inverter. Don't expect a 2000W inverter to run a 2000W load for very long and be happy about it.


There are plenty of high-quality tier-1 inverters that are in the range you are looking at.

Magnum: https://ressupply.com/inverters/magnum-energy-ms4024pae-sinewave-parallel-inverter
Outback: https://ressupply.com/inverters/outback-vfxr3524a-01-vented-invertercharger
Samlex: https://ressupply.com/inverters/samlex-evo-4024-pure-sine-wave-invertercharger
Schneider: https://ressupply.com/inverters/schneider-electric-conext-sw4024-120240-invertercharger

When I look at it I am a bit confused what is the difference between so called power inverters, battery inverters, off-grid inverters.
How I understand it I should go for a battery inverter.

Basically, all off-grid inverters are battery inverters, even the hybrid ones. Only dedicated grid-tie inverters need no battery at all, because their output is a function of the presence of the grid.

 

[JohnBrother]

I can see a couple of problems here. First,

98Voc in 2S2P configuration, 147Voc in 3S2P (future) configuration.
I want to leave some room for growth to add 2 more 460W panels so 3s2p.
For that I decided to go for Victron MPPT 150/100 battery charger.

Your Victron has a voltage limit of 150V. If you wire three panels in series, the Voc will be 147 ONLY at room temperature. How cold do your winter lows get? Below freezing? You need to multiply the Voc by a correction factor (cf) for cold weather. Right at freezing, a panel string that is 147Voc at room temperature (77F) will be 147V X 1.12cf= 165Voc. If you really want to accurately predict what the voltage of your string will be at your location's winter low, use Midnight's string calculator. https://www.midnitesolar.com/sizingTool/index.php

What does this statement mean? I was able to find a suitable MPPT with room for growth but I cannot find an inverter that can cover up to 3000W when I add 2 more panels (2760W). A component inverter's function is independent of the number of panel watts. It is the charge controller that has to be sized to the number of panel watts, not the inverter. In terms of scaling for your inverter, I recommend you use the 2X rule for sizing. That means if you expect to run a 2000W load, then get at least a 4000W inverter. Don't expect a 2000W inverter to run a 2000W load for very long and be happy about it.


There are plenty of high-quality tier-1 inverters that are in the range you are looking at.

Magnum: https://ressupply.com/inverters/magnum-energy-ms4024pae-sinewave-parallel-inverter
Outback: https://ressupply.com/inverters/outback-vfxr3524a-01-vented-invertercharger
Samlex: https://ressupply.com/inverters/samlex-evo-4024-pure-sine-wave-invertercharger
Schneider: https://ressupply.com/inverters/schneider-electric-conext-sw4024-120240-invertercharger

When I look at it I am a bit confused what is the difference between so called power inverters, battery inverters, off-grid inverters.
How I understand it I should go for a battery inverter.

Basically, all off-grid inverters are battery inverters, even the hybrid ones. Only dedicated grid-tie inverters need no battery at all, because their output is a function of the presence of the grid.

Right, I see you advocate for All-in-one system.
Am I right that these can handle up to 140VAC so there is no room for growth similar to Victron 150/100 I picked. Thanks for the Midnight's string calculator. You are right with 6 panels this would blow up the 150Vac charge controller in winter so I would have to go for Victron 250/70 or 250/100.

In this case if this is kind of half the house setup should I consider 48V system then?
and e.g. Victron Energy EasySolar-II 48V 3000VA 35A 32A MPPT 250/70 GX

It's like building a PC, there is always a temptation to go bigger.

 

[MichaelK]

Right, I see you advocate for All-in-one system.
Am I right that these can handle up to 140VAC so there is no room for growth similar to Victron 150/100 I picked. Thanks for the Midnight's string calculator. You are right with 6 panels this would blow up the 150Vac charge controller in winter so I would have to go for Victron 250/70 or 250/100.

In this case if this is kind of half the house setup should I consider 48V system then?
and e.g. Victron Energy EasySolar-II 48V 3000VA 35A 32A MPPT 250/70 GX

It's like building a PC, there is always a temptation to go bigger.

Well, no. I myself have component systems, and for my own personal use, I would never chose a HF AiO. I use Schneider inverters.

Keep in mind that the Voc of some AiO units is even lower than the Victron, so that's not a given. For my own systems I use Midnight200s. Most of my arrays are 4S, at 120VDC.

I myself am running both 24 and 48V systems. I myself started with 12V years ago, now I advise everyone to avoid 12V for any application that does not have wheels.

Here is a good rule of thumb I apply to system design.

For applications not ever needing more then 1000W, use 12V.
For applications in the 1000-2000W range, 24V is a good choice.
For applications in the 3000+W range, go with 48V

 

[LydMekk]

Go with 48V setups if possible. 12 or 24V are old style, easier to get new products that support 48V.

 

[JohnBrother]

Well, no. I myself have component systems, and for my own personal use, I would never chose a HF AiO. I use Schneider inverters.

Keep in mind that the Voc of some AiO units is even lower than the Victron, so that's not a given. For my own systems I use Midnight200s. Most of my arrays are 4S, at 120VDC.

I myself am running both 24 and 48V systems. I myself started with 12V years ago, now I advise everyone to avoid 12V for any application that does not have wheels.

Here is a good rule of thumb I apply to system design.

For applications not ever needing more then 1000W, use 12V.
For applications in the 1000-2000W range, 24V is a good choice.
For applications in the 3000+W range, go with 48V

Does it mean 48V system should be considered over 2000W? I mean because there is a gap between 2000W and 3000W according to your recommendation let's say if my usage would be 2500W. This is exactly where my issue was/is.
I reckon I go under 2000W so stick to 24V. In the next iteration I look into 48V system.

 

[MichaelK]

Does it mean 48V system should be considered over 2000W? I mean because there is a gap between 2000W and 3000W according to your recommendation let's say if my usage would be 2500W. This is exactly where my issue was/is.

It's a grey area. They make 12V inverters that supposedly go up to 3000W, but it's just a marketing ploy to sell units. I always recommend the 2X rule for design purposes. That is, if you need to power 2500W, then you should have an inverter that can support 5000W. I don't apply this to just inverters, but everything I buy. Electronics will live a much longer life if they are not pushed daily to the upper limits.

So, 5000W is mostly in 48V territory, though I suspect my Conext 4024 would handle that 2500W load just fine. For my 2000W well-pump, I went with a 48V XW+6848, and it powers that effortlessly. I've loaded the 6848 as high as 3600W in real-time, and it didn't complain. I don't like giving recommendations on equipment I haven't personally experienced performing at that level, so I'd have to say if you expect to actually see 2500W, then go with 48V now.

 

[JohnBrother]

It's a grey area. They make 12V inverters that supposedly go up to 3000W, but it's just a marketing ploy to sell units. I always recommend the 2X rule for design purposes. That is, if you need to power 2500W, then you should have an inverter that can support 5000W. I don't apply this to just inverters, but everything I buy. Electronics will live a much longer life if they are not pushed daily to the upper limits.

So, 5000W is mostly in 48V territory, though I suspect my Conext 4024 would handle that 2500W load just fine. For my 2000W well-pump, I went with a 48V XW+6848, and it powers that effortlessly. I've loaded the 6848 as high as 3600W in real-time, and it didn't complain. I don't like giving recommendations on equipment I haven't personally experienced performing at that level, so I'd have to say if you expect to actually see 2500W, then go with 48V now.

Does this 48V system look viable?

1. Victron 150V 70A MPPT https://www.victronenergy.com/uploa...oller-MPPT-150-70-up-to-150-100-VE.Can-EN.pdf
2. Victron Energy Phoenix Inverter 48/3000 Smart https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-Smart-1600VA-5000VA-EN.pdf
3. 16x 3.2V 280Ah cells
4. 4x 460W panels https://jasolar.com/uploadfile/2020/0619/20200619040220997.pdf
5. BMS

 

[MichaelK]

I would say no. If you look at the inverter specifications, it says the max "continuous" wattage for the 3000W unit is only 2400W. And that is at room temperature. At 40C it's de-rated down to 2200W. So, on a hot summer day, when you need air-conditioning, your max load drops to 2200W. So, going by the 2X rule I mentioned above, I wouldn't go with anything smaller than Victron's 48/5000.

Your panel wattage is on the low side too. I have more watts of panels on my 24V system then you would have on this 48V. You should be making an itemized list of what's going to be powered, and then figure out the panel wattage from there. In December, I'll guess that you'll be getting around 2.0 sunhours per day. So, with 2000W of panels and 2 sunhours in December, I'd say you can make 4.0kWh of power daily for that month, assuming clear weather. In cloudy/rainy weather, don't expect to get more than 0.5 sunhours.

I would double your solar wattage. Right now, today, I have 5500W online, making power on my 48V system, and later this summer I'll be adding another 2000W.

 

[JohnBrother]

ok, in this case I have to go for a AIO system I think Victron MultiPlus-II 48/5000/70-50

https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN.pdf

and up the array to 6x 480W panels.