Solar panels for an axpert inverter

**Tradie** · 27-Apr-25, 09:36 AM

It seems upgrading old gel and AGM batteries and adding solar panels to 24 VDC Axpert inverters has become the most common request.

I am currently busy with a Must PV1800 VHM series inverter.

Can we install solar panels and will it save money or just create another expensive to the budget?

Looking at the inverter Solar charger:

Max VOC - 145VDC
PV voltage range 30-130 VDC
PV input power - 1440 Watt
Max charge current - 60 amps
Efficiency - 98%

The most important information is the VOC = 145 VDC, what does it mean, when all the panels are installed and not connect to the inverter at any time of day or weather condition, the voltage cannot exceed 145VDC, otherwise it will damage the MPPT. if you decide to use 4 x 330 watt panels in parallel with a VOC of 35 VOC each, then 35X4 = 1320 Watts

Then we look at the max power of the panels, you add up the power 1440/330= 4,2 panels.

How efficient will they be, that will be determined by many factors, like roof angle, direction, etc.

Should we consider the voltage range? 30-130VDC, would the VOC of 140 VOC be too high, it shouldn't.

**Tradie** · 27-Apr-25, 09:59 AM

Lets look at other panel sizes, how many could we install.

1440/460= 3.13,

1440/550= 2.61

1440/650= 2.21

What would you need to consider, the VOC and the startup voltage which in this case is 30 VDC. It would depend on the panel configuration, if in series you could add voltage, but in parallel you the voltage would be the same

4 panels in parallel with a VOC of 40 VDC would be the same 40 VDC, pretty close to the startup, it would be better to have at least 2 in series = 80 VDC

Lets look at a canadian 650 watt panel specs

Max power 650 watt x 2 = 1300 W (within spec)

VOC = 45VDC x 2 = 90 VOC (within spec)

operating voltage 37.9VDC x 2 = 75 VDC (within sec)

Isc 18.39amps

Imp 17.16amps

Should we connect in parallel or in series?

In parallel the operating voltage would be a bit close to the startup, but could possibly work ( I would chance it)

If we connect the 2 in series the operating voltage would be 75.8 VDC (it would be a better)

If we go with series, the Imp current would stay the same at 18.39 amps (within spec)

**Tradie** · 27-Apr-25, 10:44 AM

What would you need to consider when selecting the panels to suit your application?

Panels and accessories required to install the panels.

Available roof space.

What is the saving, if any.

Some might ask why waste the money, some might say because the grid failures which have become a bigger problem than load shedding, at least they can keep the lights on longer.

Why not just sign a contract with a company which offers lifetime commitment, or take a R100 000 loan that would cost you a total of over R200 000 by the time it is paid up.

**Tradie** · 27-Apr-25, 11:03 AM

I have just installed a small axpert inverter with 2 x 12 VDC batteries, why didn't I install a proper hybrid system, like I have installed for many customers, simple, the budget. If I had R100k and needed power 24/7, then it would have been installed 3 years ago. I am also not prepared to extend the return of investment by paying back almost the loan which would add up to almost R100k in interest and charges.

Instead for R2000 and a bit of negotiating, I got a little axpert unit with 2 gel batteries that last around 6 hours with all the devices I need connected.

I have plenty of roof space so for now I think 2 x 650 in panels in parallel will be the best option for me.

The panels will be installed directly above the inverter, so there wont be long DC runs. I can install a DC combiner on the outside wall, behind the inverter, with the wiring installed in bosal conduit, which will make it safe and easier to isolate in case fo a problem.