I currently have a Sunsynk 5kw inverter with 20kw of Pylontec batteries and 5.2kw of solar (1 string of 2kw and 1 string of 3.2)

we are right at the limit of the 5kw inverter tripping it a few times as we are have added my tenants on to the system. we do have Eskom but would prefer not to use it

I have bee thinking of adding another 5kw inverter in parallel and then I would have another 2 MPPTs for 2 more strings, as I need to add more solar as well.

But the price of the 8kw is not much more than the 5kw, it might be worth selling the 5kw and adding a new 8. This would make the change over a lot easier and I would not need to add any additional wiring on the AC side to parallel a new 5kw

Any thoughts or suggestions would be greatly appreciated

3 hours ago, charl said:

I currently have a Sunsynk 5kw inverter with 20kw of Pylontec batteries and 5.2kw of solar (1 string of 2kw and 1 string of 3.2)

we are right at the limit of the 5kw inverter tripping it a few times as we are have added my tenants on to the system. we do have Eskom but would prefer not to use it

I have bee thinking of adding another 5kw inverter in parallel and then I would have another 2 MPPTs for 2 more strings, as I need to add more solar as well.

But the price of the 8kw is not much more than the 5kw, it might be worth selling the 5kw and adding a new 8. This would make the change over a lot easier and I would not need to add any additional wiring on the AC side to parallel a new 5kw

Any thoughts or suggestions would be greatly appreciated

At least with 2 inverters you do have a backup if one goes down. You also might not get a lot of money for the 5kw second hand.

The other thing is are you sure 8kw will not also trip. 10kw gives you more room.

The 8kw might also need thicker battery and ac cables so its not just a swap in and out.

Despite your hesitation I would recommend paralleling another 5kW unit. The big advantage would be to have redundancy. If one unit fails, and they will one day, you still have the other one running in case of black out, even with reduced power capacity. I did it myself - it's not such a big deal.

Remember - you also would need to add some battery capacity.

33 minutes ago, Beat said:

Despite your hesitation I would recommend paralleling another 5kW unit. The big advantage would be to have redundancy. If one unit fails, and they will one day, you still have the other one running in case of black out, even with reduced power capacity. I did it myself - it's not such a big deal.

Remember - you also would need to add some battery capacity.

A pity one could not apply the redundancy to your partner with a good outcome. 😂😂

2 hours ago, Scorp007 said:

A pity one could not apply the redundancy to your partner with a good outcome. 😂😂

Indeed, best to have one inverter at a time, otherwise you might trigger inverter envy

With the additional 5kW you'd have, as you said, additional MPPT inputs. If you're going the route of an 8kW, just consider your current configuration of panels, and how you'd re-wire them in order to make the most of the two MPPT's. For argument's sake, if you could re-arrange your existing 5.2kW of panels into two equal-length strings of 2.6kW, you could place them in parallel into one MPPT of the 8kW, and then add more of whatever other panels.

If it happens to be difficult to do that, maybe because of space or panel direction, or different types of panels, then that would speak more for adding another 5kW, rather than the 8kW.

The cheapest would be to put the tenants/flatlet as a non-essential load, and upgrade the 2.0kW string to 3.2kW also, but that's going to cause a different form of inverter envy. And it won't get you off Eskom as much, it should just prevent the tripping.

The part trick of the 5kW option is that in future, you could add a third inverter and run three phase equipment.

Thanks all for the advice. I'll be adding another 5kw. The advantages of the 2 inverters and additional power out ways the cost.

In the meantime I'll be adding a additional 5 x 555w panels. And will get the second inverter next month.

So I bought another 5 x 555w panels, But have realized that all 5 will exceed the voltage of the inverter with the existing 6 panels facing North West, So if I install all 5, but add 4 to the existing 6 the STC volts would be 499.5v and NOTC Volts would be 469.7v the amps would be well within range

I am planning to move the existing 6 x 335w panels to the North east on the second string to get the morning sun

This is all up until I get the second inverter.

Question is, Is the 499.5v to close to the 500v limit of the inverter and all the DC fuses and I will have problems?

This is based on the data sheet of the panels. But, If I look at the info on the inverter, once the batteries are full, the Voltage of the 6 existing panels spikes to 280.6v.

280.6v / 6 = 46.7v

46.7 x 10 = 467v

Under normal use and charging the sit at 255v

Max panels to be safe is 8 on a string in Series.

3 hours ago, charl said:

Question is, Is the 499.5v to close to the 500v limit of the inverter and all the DC fuses and I will have problems?

Way too close.. One lekka cold snap (coming this monday (28/07/2025) will push Voc way past 500V =💭😡 time.

Also remember, the max efficient operation Voltage of the MPPT = 450V. Anything above that decreases it's efficiency.

On 2025/07/22 at 11:33 AM, Sidewinder said:

(28/07/2025)

Pull the fuses before dawn and measure VOC with full irradiance.

On 2025/07/22 at 8:04 AM, charl said:

6 x 335w

Put the 335W panels in two parallel strings and add 2 or 3 of the 555W panels in series after a combiner.

On 2025/07/22 at 8:04 AM, charl said:

So I bought another 5 x 555w panels, But have realized that all 5 will exceed the voltage of the inverter with the existing 6 panels facing North West, So if I install all 5, but add 4 to the existing 6 the STC volts would be 499.5v and NOTC Volts would be 469.7v the amps would be well within range

I am planning to move the existing 6 x 335w panels to the North east on the second string to get the morning sun

This is all up until I get the second inverter.

On 2025/07/19 at 3:18 PM, charl said:

Thanks all for the advice. I'll be adding another 5kw. The advantages of the 2 inverters and additional power out ways the cost.

In the meantime I'll be adding a additional 5 x 555w panels. And will get the second inverter next month.

Personal 2c' worth. I wouldn't even do anything until next month when you've got the second inverter. Just install the inverter and the additional 5x555W panels to it all in one go. Those panels could generate at most around R250 worth of additional power in one month, hardly worth the changes and re-changes, and since you've got around 5.2kW of panels already installed, you're not even going to see that benefit. I'd just put the 5x555W panels straight onto the North-East side a month from now, and keep the existing panels where they are on the first inverter, and maybe later add another 3 of the 335W panel to the existing 2kW string.