PV Power Fluctuation

[Anton64]

I had 10 x 560W panels installed in 2 strings on my 5.6kw hybrid inverter. I noticed now that the power on the PV input keeps on fluctuating resulting in the battery charge being switched between the grid and PV constantly. Why would this happen?

Panel specs - 49.9v, 560W, 13A

Inverter Specs - max PV open circuit v: 450V, 27A

 

 

[mzezman]

3 minutes ago, Anton64 said:

I had 10 x 560W panels installed in 2 strings on my 5.6kw hybrid inverter. I noticed now that the power on the PV input keeps on fluctuating resulting in the battery charge being switched between the grid and PV constantly. Why would this happen?

Panel specs - 49.9v, 560W, 13A

Inverter Specs - max PV open circuit v: 450V, 27A

 

 

Generally could be caused by shade, temperature, load, clouds.

If this is happening on a clear blue sky day with constant load then there might be an issue - but we don't have that info to infer what it could be

[Anton64]

24 minutes ago, mzezman said:

Generally could be caused by shade, temperature, load, clouds.

If this is happening on a clear blue sky day with constant load then there might be an issue - but we don't have that info to infer what it could be

Thanks @mzezman. Definitely not shade, clouds, etc. What do you mean when you say it could be due to load? The load is fairly constant but I'm going to ask a very stupid question now - does the power shown on the inverter normally show what is being used or what is generated i.e. if it reports 230v, 55W is that what is currently being used or is that what the panels are generating?

[Bobster.]

So the first thing is that PV can fluctuate according to conditions. Even on mostly clear days the odd cloud may pass over.

Unless your system set to export it's excess power, once the battery is charged the system will draw just enough PV to service the loads. 

Look at my system today

Green line is SOC. Blue line is PV. Yellow line is load.Purple line is battery - below the axis it is charging, above it is discharging.

1) Although it's a clear, blue sky day (every time I look out the window) there has been some cloud and it causes the available PV to vary.
2) Once the battery is charged you can see the PV that the system is drawing being reduced to just enough service the load.
3) At one point you can see loads go up, system draws from battery because there's not enough PV, but then draws full PV for a few minutes to charge the battery up again. 

There's nothing unusual about this. All quite usual behaviour. The only way that the afternoon use of PV would go up is if I increased the loads or if I was exporting my surplus.

Do you have a graph something like this that illustrates the behaviour that has you concerned? I suspect that would help us. Be prepared for questions about what inverter you have and about the settings.

[Anton64]

Thanks @Bobster., unfortunately, I do not have a graph. I use really crap solarpower app but mostly observe this behavior by watching the display in the inverter.

[mzezman]

6 minutes ago, Anton64 said:

Thanks @Bobster., unfortunately, I do not have a graph. I use really crap solarpower app but mostly observe this behavior by watching the display in the inverter.

A good test is once the batteries are full, turn on a high power device, kettle or microwave then see what happens. The load should jump up and within a few seconds the solar generation should also jump to match this new load

@Bobster. is spot on with this analysis

[Anton64]

Will do that (was going to say tonight DUH) later today or tomorrow and see what happens. What I did do in a similar vain is to disconnect the grid and battery, switch on a whole lot of smaller stuff (don't have any high-power devices just yet) and the PV power did go up, BUT (and this I find strange) it still fluctuated with the peaks now much higher due to the extra load. The lows were definitely lower than the total load yet everything just ticked over without an issue.