Oversizing Solar Panel Array - can my inverter handle it?

[AlexanderKristiansen]

I have a Voltronic 24V 2400W all-in-one inverter and a 1Kw solar array. According to the manual, it can handle 1Kw of solar power. I called the dealer and asked about what would happen if I oversized my solar array and if this could damage my inverter.

He told me putting more than 1Kw into the inverter would "fry it", but my impression was that he was quite new at his job and a "newbie".

According to the manual (see attachment) I can set a limit of a maximum of 40A of solar charging. Why would there be a 40A limit, if my inverter would get fried if I "overload" my inverter? It doesn't make any sense to me.

Isn't the limit of maximum solar charging what is referred to as "clipping"?

Any inputs?

 

[sunshine_eggo]

Generally speaking, if you do not exceed the PV voltage input limit AND the charge current rating on the input side (40A in your case), the unit should handle the over-panel. Some units like Victron list a PV input current limit that is lower than the charging limit, and it should be respected.

Voltronics is the manufacturer of the MPP Solar and Growatt units. Many people have over-paneled them to varying degrees.

Example:

Assuming your Max PV input is 145V.

250W, 60 cell panels likely put out about 30Vmp and 8.3A.

3S would be 90Vmp @ 8.3A j= 750W
You could parallel 3-4 strings and still stay under PV 145Voc and 40A input.

Thus you could likely put 3000W on your unit and be safely under all limits. The only concern that I have is that you're running cheap Chinese hardware at its absolute maximum power for hours rather than a brief period compared to a "right-size" array. You could gain some goody with opportunistic panel orientations, e.g., 3 arrays: 750W SE, 750W S, 750W SW, which would give you lower peak power, but provide more even power for longer periods of time.

 

[AlexanderKristiansen]

Hi and thanks for your reply. The voltage range for the inverter is 30-80Vdc

I have 4x275W panels, two and two wired in series. The voltage for each panel is 32V.

Each panel is 8.61A so two in series will still be 8.61, but the voltage increase to 64? Times 2 is 17,22, so wel belowl 40A?

I have been running the 1Kw array without any issues for a year. During cold periods the sun is behind some trees so I never get maximum charging from the panels during cold periodes.

The reason I want to oversize my solar array is that during the winter we only have a few hours with sunlight and hardly any charging. So I need more panels to keep my batteries from draining and I want to put the new array in a new location with better charging during the winter.

Early 2022 I will upgrade to the Victron EasySolar II and get rid of the "cheap Cinese hardware".

Do you think I can double my solar array to 8x275W panels, 8.61x4=34.44, and still under 40A?

 

[sunshine_eggo]

275W/8.61A = 32Vmp

When considering the 80V limit, you need to look at Voc. You need to allow for cold weather voltage spikes. A typical array will put out 8-10% higher voltage than the data label says due to cold temps.

I'm guessing the Voc is around 38.5V, so you are already dangerously close to your 80V limit on Voc and risk damaging your MPPT. If your ambient temps ever get lower than 15°C, you may blow out your MPPT due to over-voltage.

As it stands, your panels should likely be used only in a 4P configuration. I do not see that you can safely increase your array UNLESS it NEVER gets chilly in your region.

 

[AlexanderKristiansen]

Hi and thanks again.

It does get chilly in my region, every year 10-15 degrees below zero. But as I wrote, I have had no issues with the 4x275 panels for over a year in cold conditions. 64V + 10% is still only 70V....

And the Max. PV Array Open Circuit Voltage is 100Vdc.

If I increase my array, the voltage will not increase, so why do you think increasing the array will cause any problems when I will be below 40A?

 

[sunshine_eggo]

Hi and thanks again.

It does get chilly in my region, every year 10-15 degrees below zero. But as I wrote, I have had no issues with the 4x275 panels for over a year in cold conditions. 64V + 10% is still only 70V....

And the Max. PV Array Open Circuit Voltage is 100Vdc.

If I increase my array, the voltage will not increase, so why do you think increasing the array will cause any problems when I will be below 40A?

Ah. You were giving me the MPPT range, not the absolute range. Gotcha.

2S4P array should be fine.

 

[AlexanderKristiansen]

Ah. You were giving me the MPPT range, not the absolute range. Gotcha.

2S4P array should be fine.

Great, thanks!

But do you know why the specifications say max. 1000w PV Array Power but the maximum PV input is 40A? It doesn't add up.

See attachment.

 

[sunshine_eggo]

The 40A is a CHARGE current limitation, i.e., that's the maximum power the unit can use delivering 40A to the 24V system.

In the absence of a PV current limit, the battery charge current limit is assumed to apply to the PV side.

An MPPT controller is a sophisticated DC-DC converter. The output side of the converter is limited to 40A - it will never pull more than that due to its own internal limitations - literally programmed limits. If there is additional PV power available when the MPPT is at 40A output, it jut goes unused.

 

[AlexanderKristiansen]

So in your opinion, it's wrong that my inverter will get "fried" if I go above the 40A limit?

 

[sunshine_eggo]

So in your opinion, it's wrong that my inverter will get "fried" if I go above the 40A limit?

I refer you to my previous statement:

Ah. You were giving me the MPPT range, not the absolute range. Gotcha.

2S4P array should be fine.

 

[AlexanderKristiansen]

Ok, thanks

 

[Bud Martin]

Just look at it this way, the AC outlet in the US can supply 120V up to 15A = 1800W, so if you only plug in 100W lamp into the socket the lamp will only PULL 100W from the outlet, so basically the SCC PULLS the needed power from panels to charge the batteries up to the max SCC charger limit.