Good day... I currently have 1 x sunsynk 5kw ( SUNSYNK-5K-SGO1LP1 inverter ), two Sunsynk Sun-Batt-5.32 and 12 x 450w panels. I am wanting to upgrade the system, so either buy another 5kw inverter or sell the 5kw and buy a 8kw or 10 kw inverter (Sunsynk). I did purchase the original Sunsynk 5kw inverter from the Powerstore sometime ago ( + - 5 years ago) and am worried that the current Sunsynk 5kw inverters are not compatible with the old ones when setup in parallel format. Anybody have some advice going forward?

On the matter of 2 vs 1, I recommend 2 in parallel. If one fails you still have half your supply working and can continue albeit at reduced available power.

@DAVID-EC

The answer lies in your requirements.

Pro's:

Like @zsde says, if reliability is a must e.g. people in house requiring life-support equipment, then go parallel.

Parallel is a good option, if you have run out of (mostly) north facing roof, and only have East/West left, then you score 2 extra MPPT's to add to the original 2.

Less cost. One 5kW + installation is probably going to be a lot cheaper than flogging the 5kW and getting a new 10kW.

Cons:

Parallel is always more complex to install.

More costly. Wiring etc. And you would need to add more batteries, depending on the reason for upgrade.

From what I've seen parallel installation don't behave exactly the same as a single unit.

For standard household installations I would go with a single, bigger Inverter.

I don't think your older model will not be compatible with the newer 5kW models, just make sure they are on the same firmware level before you upgrade.

If overloading was you main issue, then be careful if you go the single route. A 8kw SS can only sustain 128A (6.4kW) from DC (batteries) at night with loadshedding.

So if you requirement is more than that, rather go for the next up model, e.g. 10kW.

I'm currently running 2x5Kw Sunsynks with no issues. Manufacture dates of the inverters are over 1yr apart but they are on the same firmware and provide great functionality in parallel. It is true there is a bit more complexity but its also set and forget, You change the settings on one and they cascade to the other without you needing to do anything. Redundancy is key for me hence i got the 2x5 vs 1x8 / 10

On 2026/03/12 at 12:10 PM, Sidewinder said:

@DAVID-EC

The answer lies in your requirements.

Pro's:

... Parallel is a good option, if you have run out of (mostly) north facing roof, and only have East/West left, then you score 2 extra MPPT's to add to the original 2.

Cons:

... If overloading was you main issue, then be careful if you go the single route. A 8kw SS can only sustain 128A (6.4kW) from DC (batteries) at night with loadshedding.

So if you requirement is more than that, rather go for the next up model, e.g. 10kW.

I agree that redundancy is good, especially if one plans to go fully off-grid.

Something else to consider: The "self consumption" or "idle power" of two smaller units (say 80W per inverter on the 5kW Sunsynk) vs one larger unit (say 100W for the 8kW Sunsynk). This 1.4kWh per day wastage is not significant, but will be more important for someone living in an area of less PV power (such as Cape Town) and/or with smaller battery capacity.

Edited March 14Mar 14 by HennieL

I never really understood this logic.

Components have a MTBF rating (Mean Time Before Failure) which is a manufacturer's estimation of the average time that a component would last before if failed, requiring replacement. For an inverter this may be (for arguments' sake) 100,000 hours (under pristine conditions) but in reality between 60,000 and 90,000 hours.

If two inverters are placed in parallel, both are working, heating up and cooling down. The odds of them both failing together is fairly high if that are connected to the same circuitry and the root cause is external. Let's say, for arguments' sake we put the odds at 30%. That means that 70% of the time, one will remain working. So we have degraded service, resulting in the shedding of some (hopefully unimportant) loads, but not a complete outage. But because that one is taking on at least some additional load (assuming that there is headroom) it will heat up more, and increase its chances of failure due to these increased loads. So the chances are greater that it will also fail in the time that it takes to source and replace, or repair and replace the failed unit. Let's say by another 30%. And then it also still has its MTBF rating. When two components are placed in parallel, you effectively halve the MTBF rating of both components. So a rating of 60,000 hours becomes 30,000 hours, increasing its chances of failure overall, at the outset, not only once one fails.

To me, if a component is that important, then it should be backed up by a similar component in the cupboard, not one working in parallel.

Does anyone other than myself see this, or not?

10 minutes ago, Yellow Measure said:

I never really understood this logic.

Components have a MTBF rating (Mean Time Before Failure) which is a manufacturer's estimation of the average time that a component would last before if failed, requiring replacement. For an inverter this may be (for arguments' sake) 100,000 hours (under pristine conditions) but in reality between 60,000 and 90,000 hours.

If two inverters are placed in parallel, both are working, heating up and cooling down. The odds of them both failing together is fairly high if that are connected to the same circuitry and the root cause is external. Let's say, for arguments' sake we put the odds at 30%. That means that 70% of the time, one will remain working. So we have degraded service, resulting in the shedding of some (hopefully unimportant) loads, but not a complete outage. But because that one is taking on at least some additional load (assuming that there is headroom) it will heat up more, and increase its chances of failure due to these increased loads. So the chances are greater that it will also fail in the time that it takes to source and replace, or repair and replace the failed unit. Let's say by another 30%. And then it also still has its MTBF rating. When two components are placed in parallel, you effectively halve the MTBF rating of both components. So a rating of 60,000 hours becomes 30,000 hours, increasing its chances of failure overall, at the outset, not only once one fails.

To me, if a component is that important, then it should be backed up by a similar component in the cupboard, not one working in parallel.

Does anyone other than myself see this, or not?

He has a old one and a brand new one then. Would that not make them fail far apart of they do fail?

Also lets say they are the same age. If they do fail even a just a week or a few days apart you can get a replacement fast while not being 100% down?

Just a few days to ship a new unit to get you up again

Edited March 16Mar 16 by Stefan Cornelissen

52 minutes ago, Yellow Measure said:

I never really understood this logic.

Components have a MTBF rating (Mean Time Before Failure) which is a manufacturer's estimation of the average time that a component would last before if failed, requiring replacement. For an inverter this may be (for arguments' sake) 100,000 hours (under pristine conditions) but in reality between 60,000 and 90,000 hours.

If two inverters are placed in parallel, both are working, heating up and cooling down. The odds of them both failing together is fairly high if that are connected to the same circuitry and the root cause is external. Let's say, for arguments' sake we put the odds at 30%. That means that 70% of the time, one will remain working. So we have degraded service, resulting in the shedding of some (hopefully unimportant) loads, but not a complete outage. But because that one is taking on at least some additional load (assuming that there is headroom) it will heat up more, and increase its chances of failure due to these increased loads. So the chances are greater that it will also fail in the time that it takes to source and replace, or repair and replace the failed unit. Let's say by another 30%. And then it also still has its MTBF rating. When two components are placed in parallel, you effectively halve the MTBF rating of both components. So a rating of 60,000 hours becomes 30,000 hours, increasing its chances of failure overall, at the outset, not only once one fails.

To me, if a component is that important, then it should be backed up by a similar component in the cupboard, not one working in parallel.

Does anyone other than myself see this, or not?

MTBF doesn't work like that. Putting two inverters in parallel does not halve the MTBF of the system. In reliability engineering a parallel system actually increases system availability because both units must fail before total loss of supply occurs.

What you are describing is common-mode failure (lightning, grid surge, battery faults etc.) where both units can fail from the same external cause. That is a valid concern.

In practice parallel inverters often run at lower individual loads which can actually reduce thermal stress and extend component life.

The real trade-off between 2×5 kW and 1×10 kW is therefore system complexity vs redundancy, not MTBF.

2 minutes ago, TaliaB said:

MTBF doesn't work like that. Putting two inverters in parallel does not halve the MTBF of the system. In reliability engineering a parallel system actually increases system availability because both units must fail before total loss of supply occurs.

What you are describing is common-mode failure (lightning, grid surge, battery faults etc.) where both units can fail from the same external cause. That is a valid concern.

In practice parallel inverters often run at lower individual loads which can actually reduce thermal stress and extend component life.

The real trade-off between 2×5 kW and 1×10 kW is therefore system complexity vs redundancy, not MTBF.

💯 true

It seems the parallel concept is sometimes misunderstood, and eliminating a single point of failure is underrated.

5 hours ago, Stefan Cornelissen said:

He has a old one and a brand new one then. Would that not make them fail far apart of they do fail?

If there is an external cause for the failure, like a surge from the grid for example, then both could fail at the same time.

If the cause is something internal to the inverter, like component failure, then the MTBF comes into play. The M in MTBF stands for Mean, an arithmetic mean, so whilst it could happen at any time, logically an inverter that has worked 60,000 hours would have a greater chance of failure than an inverter that has worked for, say, 240 hours. But it does not eliminate it.

5 hours ago, Stefan Cornelissen said:

Also lets say they are the same age. If they do fail even a just a week or a few days apart you can get a replacement fast while not being 100% down?

Just a few days to ship a new unit to get you up again

That's what I stated, degraded service. My point was that the odds (probability) of failure is doubled by adding an inverter in parallel, and tripled by adding two etc.

5 hours ago, TaliaB said:

In reliability engineering a parallel system actually increases system availability because both units must fail before total loss of supply occurs.

If system availability allows for degraded operation, yes.

A parallel system would lose capacity, whereas a system with a redundant component would increase system availability.

5 hours ago, TaliaB said:

MTBF doesn't work like that.

Please tell me how MTBF works.

4 hours ago, Yellow Measure said:

If system availability allows for degraded operation, yes.

A parallel system would lose capacity, whereas a system with a redundant component would increase system availability.

Please tell me how MTBF works.

MTBF is a statistical measure, not a lifespan. It represents the average failure rate of a population, not how long a specific unit will last.

Putting two inverters in parallel does not halve their MTBF. Each unit still has the same failure rate, but system reliability improves because both units must fail before total loss occurs.

The real risk in parallel systems is not MTBF, but common-mode failures such as surges, battery faults, or wiring issues that can take out both units simultaneously.

In practice inverter failures are rarely random MTBF events. Most failures we see in the field are due to surges, heat, battery issues or installation faults. Running two inverters in parallel does improve resilience against small component failures like fans or relays, allowing the system to continue operating at reduced capacity. However, it does not protect against common-mode failures such as lightning, grid surges or battery faults, where both units are typically affected simultaneously.

So the real trade-off is not MTBF, but complexity vs partial redundancy. Proper surge protection, earthing and installation quality will have a far bigger impact on system reliability than choosing between 1×10kW or 2×5kW.

13 hours ago, Yellow Measure said:

I never really understood this logic.

Components have a MTBF rating (Mean Time Before Failure) which is a manufacturer's estimation of the average time that a component would last before if failed, requiring replacement. For an inverter this may be (for arguments' sake) 100,000 hours (under pristine conditions) but in reality between 60,000 and 90,000 hours.

If two inverters are placed in parallel, both are working, heating up and cooling down. The odds of them both failing together is fairly high if that are connected to the same circuitry and the root cause is external. Let's say, for arguments' sake we put the odds at 30%. That means that 70% of the time, one will remain working. So we have degraded service, resulting in the shedding of some (hopefully unimportant) loads, but not a complete outage. But because that one is taking on at least some additional load (assuming that there is headroom) it will heat up more, and increase its chances of failure due to these increased loads. So the chances are greater that it will also fail in the time that it takes to source and replace, or repair and replace the failed unit. Let's say by another 30%. And then it also still has its MTBF rating. When two components are placed in parallel, you effectively halve the MTBF rating of both components. So a rating of 60,000 hours becomes 30,000 hours, increasing its chances of failure overall, at the outset, not only once one fails.

To me, if a component is that important, then it should be backed up by a similar component in the cupboard, not one working in parallel.

Does anyone other than myself see this, or not?

I agree that having a spare in stock rather than in use is a good practice (if we can afford it).

Otherwise I fall between two stools.

If I have two inverters, same make and model, same age, in parallel then I increase the number of components and so the chance of an inverter failing actually increases for failures due to component failure.

But the likelihood of losing all functionality will decrease. The two are unlikely to have the same component failure at the same time. One inverter will fail, but the other remains in service and so I have some backup.

Caveats:
1) All odds are off for failures caused by something external EG power surge. Though Bob poking around the insides of the inverter is also external, and hopefully after I blow up one I learn my lesson and let the second be.

2) The two inverters would not be backing up the same circuits. So I might keep the pool pump and outbuildings going, but lose supply to the main house. But somebody who knows what they're doing can swap the connections around, or some sort of change over switch could be put in place. I would lose backup on some circuits - unless we can add the outputs of the two inverters so that a failure of one inverter will give us same circuits backed up but we have to be more careful with what we switch on.

Edited March 17Mar 17 by Bobster.

3 hours ago, TaliaB said:

• Putting two inverters in parallel does not halve their MTBF.

Agreed, I stand corrected (in the strict technical sense), but then allow me to re-phrase: Putting two inverters in parallel operation increases the probability of inverter failure by 2. That's the law of averages at work, and I am not prepared to debate it 😄.

It also creates redundancy (hot standby) if, and only if:

1. A system fault arises due to an inverter failing, and not an external cause;

2. The system has capacity to operate under the exact same same load conditions (i.e in normal parallel operation no inverter exceeds 50%);

3. The faulty unit can be repaired, or another sourced, and replaced, in a reasonable timeframe (and hopefully a maintenance slot).

It creates derated redundancy (degraded performance) if only 1 and 3 are true.

Not everyone's needs are the same, and this may appeal to some, depending on business case and application.

I would agree with you that external causes are far more common though, and therefore cold standby is also a good option (i.e. buying 2 inverters, putting only one into operation, and store the other in a cool, dry place.

The advantages over a parallel system would therefore be:

• Simplicity vs complexity;

• Less chance of an external fault affecting the second inverter;

• Less probability of inverter failure; and

• Replacement is on site, no waiting for repairs or container ships to offload.

The only disadvantage that I could see would be an outage at a potentially inconvenient moment, but it could soon be rectified. So if availability is a thing, cold standby is a good option, and in some cases even better.

8 minutes ago, Bobster. said:

I agree that having a spare in stock rather than in use is a good practice (if we can afford it).

Otherwise I fall between two stools.

If I have two inverters, same make and model, same age, in parallel then I increase the number of components and so the chance of an inverter failing actually increases for failures due to component failure.

But the likelihood of losing all functionality will decrease. The two are unlikely to have the same component failure at the same time. One inverter will fail, but the other remains in service and so I have some backup.

Caveats:
1) All odds are off for failures caused by something external EG power surge. Though Bob poking around the insides of the inverter is also external, and hopefully after I blow up one I learn my lesson and let the second be.

It is not often that you and I agree, so I double-checked just to be sure 😁

Spot on!

8 minutes ago, Bobster. said:

2) The two inverters would not be backing up the same circuits. So I might keep the pool pump and outbuildings going, but lose supply to the main house. But somebody who knows what they're doing can swap the connections around, or some sort of change over switch could be put in place. I would lose backup on some circuits - unless we can add the outputs of the two inverters so that a failure of one inverter will give us same circuits backed up but we have to be more careful with what we switch on.

Yes, or it could the the form of an inverter that is pre-wired, mounted against the wall, and ready to pump electrons at the flick of a switch (or two). That's what I would refer to as a "Warm Standby".

1 hour ago, Yellow Measure said:

Agreed, I stand corrected (in the strict technical sense), but then allow me to re-phrase: Putting two inverters in parallel operation increases the probability of inverter failure by 2. That's the law of averages at work, and I am not prepared to debate it 😄.

The arithmetic is straight forward: If the chance of a stand alone inverter failing is 1 in 100, then with two in parallel
1) The chance of either inverter failing is now 2 in 100.
2) The chance of losing both inverters at the same time is now 1 in 10000

If it's a logical OR (Inverter A fails or inverter B fails) then we deal with the sum of the probabilities. If it's a logical AND (A fails AND B Fails) then we deal with the product of the probabilities.

If A fails, then the chance of B failing is now 1 in 100 as we are down to one inverter.

Having them in parallel increases the chance of one of them failing, but reduces the chance of a total loss of backup.

Edited March 19Mar 19 by Bobster.
Clarity (I hope)

On 2026/03/12 at 10:59 AM, DAVID-EC said:

Good day... I currently have 1 x sunsynk 5kw ( SUNSYNK-5K-SGO1LP1 inverter ), two Sunsynk Sun-Batt-5.32 and 12 x 450w panels. I am wanting to upgrade the system, so either buy another 5kw inverter or sell the 5kw and buy a 8kw or 10 kw inverter (Sunsynk). I did purchase the original Sunsynk 5kw inverter from the Powerstore sometime ago ( + - 5 years ago) and am worried that the current Sunsynk 5kw inverters are not compatible with the old ones when setup in parallel format. Anybody have some advice going forward?

Ok, lots of off-topic postings, let me muddy the waters waters by throwing in my 5 zim-cents worth...

If all you need is more kW power from your inverter, but not more solar production options, then two 5kWatters are fine, but... looking into the future and maybe even now, where you may want to add more solar panels to produce more power, the 5kWatters are a bad idea, they are limiting the current on the PV inputs such, that quite a few panels that are available these days won't foot the bill and you may struggle to find panels that will work well with the Sunsynk/Deye 5kW inverters. The 8kWatters are a better option and looking at Solis should not be off the table either.

Going back off on a tangent. It's fair to say that the current Solis inverters have surpassed the older Sunsynk and Deye models that have been on sale in recent years, both in terms of specifications, and value for money.

Maybe we should be asking how the newer Deye models stack up, and I think it was touched on some time ago. For example the Deye SG04LP1-EU 6kW is a more appropriate competitor for the Solis S6 6kW hybrid.

Looking for someone to wade through the muddy waters and do the comparison. If it takes some mud-slinging along the way, why not.

3 hours ago, Kalahari Meerkat said:

If all you need is more kW power from your inverter, but not more solar production options, then two 5kWatters are fine, but... looking into the future and maybe even now, where you may want to add more solar panels to produce more power, the 5kWatters are a bad idea, they are limiting the current on the PV inputs such, that quite a few panels that are available these days won't foot the bill and you may struggle to find panels that will work well with the Sunsynk/Deye 5kW inverters. The 8kWatters are a better option and looking at Solis should not be off the table either.

Agreed, so then the logical thing to do would be to install TWO 10kW units, just to be safe AND sure (statistically speaking) 😁😁

This is going to become very expensive, very quickly 😇

1 hour ago, HennieL said:

to install TWO 10kW units

Did nobody read what @DAVID-EC wrote? Either another 5kW in parallel or a single 8 or 10kW, The doubling up on everything was somewhat off topic....

I have a bit of a different take personally. I view things from a ROI point of view. I would get 1 10kW and not care for redundancy. Why? Modern inverters last for years. Why have 2 to plan for an outcome that will happen once in say 5 years? If one is grid connected, use it. That is your silent generator right there. Will it kill a person to use the grid while getting a replacement inverter or the inverter repaired? I dont think so.

If one of the 2 inverters dies after 5 years and it cant be repaired, you are stuck with one small inverter and will be forced to buy 2 again. The other will be sold for next to nothing on the used market. I could see it working if the 1 10kW is that much more expensive than 2 5kW inverters which I am skeptical it is.

I have no redundancy for the inverter and am not grid connected and have no worries. But I operate from a perspective of not spending time or money on repairs. When the inverter fails, I get another one the same day or the following day and in 30 minutes I can install it. The broken inverter will probably be listed for sale and be of use to someone else willing to repair it and give it life again.

But I also dont/wont spend money on inverters that cost over 20k. I will stick to the Axpert clones that retail for cheap. I can get a 6.2kW for around 6k or a 11kw for around 10k. This is from brands that have been around for years now because I dont believe the big name brands last longer than the clones out there.

That is my take basically. I have no generator (I hate them) and have 1 inverter only. I spent 3300 on it and it has run flawlessly for a year. When the time comes as mentioned, I can purchase and install it in a matter of hours. For people grid connected, there is no reason in my opinion for the word redundancy to be a point of discussion unless it takes weeks/months for an inverter to get repaired and you have constant power cuts.

Edited March 17Mar 17 by Denns

22 hours ago, Yellow Measure said:

I never really understood this logic.

Components have a MTBF rating (Mean Time Before Failure) which is a manufacturer's estimation of the average time that a component would last before if failed, requiring replacement. For an inverter this may be (for arguments' sake) 100,000 hours (under pristine conditions) but in reality between 60,000 and 90,000 hours.

If two inverters are placed in parallel, both are working, heating up and cooling down. The odds of them both failing together is fairly high if that are connected to the same circuitry and the root cause is external. Let's say, for arguments' sake we put the odds at 30%. That means that 70% of the time, one will remain working. So we have degraded service, resulting in the shedding of some (hopefully unimportant) loads, but not a complete outage. But because that one is taking on at least some additional load (assuming that there is headroom) it will heat up more, and increase its chances of failure due to these increased loads. So the chances are greater that it will also fail in the time that it takes to source and replace, or repair and replace the failed unit. Let's say by another 30%. And then it also still has its MTBF rating. When two components are placed in parallel, you effectively halve the MTBF rating of both components. So a rating of 60,000 hours becomes 30,000 hours, increasing its chances of failure overall, at the outset, not only once one fails.

To me, if a component is that important, then it should be backed up by a similar component in the cupboard, not one working in parallel.

Does anyone other than myself see this, or not?

I agree, with two inveters you double your chances of something actually failing.

1 hour ago, Kalahari Meerkat said:

Did nobody read what @DAVID-EC wrote? Either another 5kW in parallel or a single 8 or 10kW, The doubling up on everything was somewhat off topic....

Don't take everything so seriously guys - the two x 10kW inverters was tongue in cheek - it's always good to just see the funny in a situation/discussion, and rather have a smile than a frown 😁😁

On 2026/03/12 at 10:59 AM, DAVID-EC said:

Good day... I currently have 1 x sunsynk 5kw ( SUNSYNK-5K-SGO1LP1 inverter ), two Sunsynk Sun-Batt-5.32 and 12 x 450w panels. I am wanting to upgrade the system, so either buy another 5kw inverter or sell the 5kw and buy a 8kw or 10 kw inverter (Sunsynk). I did purchase the original Sunsynk 5kw inverter from the Powerstore sometime ago ( + - 5 years ago) and am worried that the current Sunsynk 5kw inverters are not compatible with the old ones when setup in parallel format. Anybody have some advice going forward?

Can I ask why you want to upgrade? Why only the inverter? the system seems to be balanced, so upgrading only one component may not offer huge benefits.

R.

21 hours ago, GreenFields said:

Looking for someone to wade through the muddy waters and do the comparison. If it takes some mud-slinging along the way, why not.

Got my waders on let's test the waters.Some pro and cons.

Deye SG04 6kW

Higher PV current tolerance. Strong parallel scalability (up to 16 units). Better suited to off-grid, rural, and complex hybrid systems. Passive cooling simple and robust

Solis S6 Pro 6kW

Wider MPPT voltage window and lower startup voltage. Faster transfer time (<4 ms). More advanced grid interaction and energy management. Better suited to grid-tied and compliance-driven installs.

While we at it let's add the Luxpower LUX6KW hybrid to the mix right in the price range of Solis.