My system was installed in 2015 and consists of 4 x 260 watt PV panels. a 3kVA inverter and 400 a/h Blue Nova battery. Its a 24V system

I am getting a 48V inverter and Blue Nova can convert the battery to 52 volts for a nominal sum

I'd like to fit at least another 2 PV panels, as the roof space can manage another two

But the smallest PV panels today seem to be 300 watt units for the smallest. Any tips on how to combine the two sets? There are 2 pairs of panels in series, the pair in parallel
 

 

14 minutes ago, chrisc said:

But the smallest PV panels today seem to be 300 watt units for the smallest. Any tips on how to combine the two sets? There are 2 pairs of panels in series, the pair in parallel

Depends on the inverter and what it can handle Voltage and current wise and it may be impossible to make 2 new panels work on the same MPPT with the new inverter, but, possibly the inverter has 2 MPPTs and that may be doable...

As above, it will depend on your new inverter. Please provide make and model.

Its a RTC Axpert 5000VA

The spec sheet states:

 

SOLAR CHARGER

Maximum PV Array Power 3000 W

MPPT Range @ Operating Voltage 60VDC ~115VDC

Maximum PV Array Open Circuit Voltage 145 VDC

Maximum Charging Current 60A

 

I see 275W Mecer panels are available for just under R2000 each

 

 

 

Edited November 26, 20223 yr by chrisc
left something out

That 275W Mecer panel looks close, like you could add one onto each string of 2x260W Yingli panels (2+1) in parallel with (2+1).

Should just be clear that with these panels in this configuration you will not get close to the maximum power that the inverter can handle, you could have used a completely different set of panels with a higher voltage and current capacity, but if you don't have more roof space that could be a moot point.

2 hours ago, chrisc said:

I see 275W Mecer panels are available for just under R2000 each

The Vmp and Imp numbers are close enough that changing your 2S2P strings to 3S2P with one Mecer panel added to each existing string is probably a pretty good option... but even if you want to keep the new panels separate and end up with 2S3P, that should also be fine...

Let's see Voc for existing = 37.7V you have two, so 75.4V add a new panels @38.6V, that would be 114V still withing limits and they would only reach this when there's no load, so this seems like the best option, I'd say 3S2P with one 275W Mecer panel added to each series string.

Thanks for all the replies. they have been helpful

I could replace all 4 panels with higher generating ones and achieve more efficiency

One could go on and on, but is the expense warranted?  I think not

I will therefore fit 2 of the 275 watt panels and compare the output to the 260 watt panels.  The earlier ones have no doubt dropped in efficiency, seeing they are 7 years old now

Most 60 cell panels will be in the right voltage range. You can also look at some other sizes like 280W. Just try to get the Imp close to the current 8.8A or higher. I would also go for 3S2P to reduce the current instead of 2S3P.

Personally I would not buy new panels just because the current ones are already 7 years old. The degrading I would guess will be small. For future you can even go to 3S3P or more parallel sets via a combiner box although it seems like space would be the limiting factor.