EURENER STRING LOW VOLTAGE ON HOT SUNNY DAYS

[bobbiecool]

Hi. I had installed last November a Growatt SPH5000 inverter, a Growatt 6.5kw battery and 18 Eurener 28v 410w panels, 2 strings of 12 and 6. I encountered a problem last week when I noticed spiking from lunchtime to sunset, these were hot cloudless days. I assumed it was too much voltage coming in from the grid, however after talking to UK Power Networks they assured me voltage was normal all week coming in to my property. I contacted Growatt (who are always very helpful) and from the info I gave them and the readings they can see at their end they said the voltage required to generate power on the string of 6 panels was not enough, it was tip toeing around 150v (the minimum required) and would also drop well below that. After some investigation I read that in hot sunny days panel voltage can drop, hence my issue
. An electrician was sent out to investigate yesterday, he volt tested each panel on the 6 string and they each came out at 24v, and not 28v which they should have been, which obviously made things much worse.
My question is what sort of voltage drop should one expect in the summer, and shouldn't there be a minimum voltage to compensate for the drop?
Any help would be appreciated.

 

[DIYrich]

I found a MEPV 80 datasheet for 410w panels with vmp of 23.46 at 1000 W/m2 25c. The MEPV 108 is 31.45v. Can you link to a 28v version of the panel.

 

[littleharbor2]

Most likely referring to the Voc. of that panel.

https://eurenergroup.com/wp-content/uploads/2023/05/Eurener_MEPV-80_HALF-CUT_410Wp_2023EN.pdf

 

[bobbiecool]

That's the one, the voc is 28.15, which I'm told by the electrician is the figure that's important (im not an electrician myself )

 

[littleharbor2]

That Voc. number is important when designing your PV wiring scheme based on the lowest expected temperatures in your area. As far as the number you are asking about, the Vmp it is the voltage of a panel under load and it could be that high but likely it will be a bit lower due to the daytime temperature the panel's surface will experience.

 

[TomC4306]

Hmm.
Panels Imp is 17.48 amps.
Inverters max input current per input is 12 amps.
Plus, MPPT voltage range is 150-550
6 panels at 23v is 138
These two pieces of hardware don't seem particularly well matched.

 

[bobbiecool]

Hmm.
Panels Imp is 17.48 amps.
Inverters max input current per input is 12 amps.
Plus, MPPT voltage range is 150-550
6 panels at 23v is 138
These two pieces of hardware don't seem particularly well matched.

With the little I have learnt I agree. Growatt suggest adding another panel to the string, which unfortunately cannot be done. The installers will have to fit 6 new panels at a higher voltage, would I be correct in assuming this? MCS has already been informed of my issue.

 

[TomC4306]

With the little I have learnt I agree. Growatt suggest adding another panel to the string, which unfortunately cannot be done. The installers will have to fit 6 new panels at a higher voltage, would I be correct in assuming this? MCS has already been informed of my issue.

Instead of 2 strings, 12 panels and 6 panels, why not 2 strings, 9 and 9?
This still will not address your overcurrent problem. With that inverter they should have used different panels or with those panels they should have used a different inverter.

 

[bobbiecool]

One thing I neglected to mention was the voltage test was a VOC test on each individual panel, which all came out at 24v. If they were the panels shown on the data sheet above that would be bad enough, however they cannot be the panels that were installed.

 

[bobbiecool]

Instead of 2 strings, 12 panels and 6 panels, why not 2 strings, 9 and 9?
This still will not address your overcurrent problem. With that inverter they should have used different panels or with those panels they should have used a different inverter.

Could you explain why that would be please?

 

[TomC4306]

Could you explain why that would be please?

When solar panels are connected in series, voltage is additive current is not. So, 12 panels in series makes a little less than 300 volts which is comfortably in the range of the device they are attached to. But six in series do not reach the minimum voltage of that device. If they were reconfigured to 9 in each string you would have 220 volts per string and both strings would then be within the range of voltage required by the mppt.
Each string is running at 17 amps. The maximum input current of the device they are attached to is 12 amps. 17 is greater than 12.

Edit - pretty basic stuff that paid installer should know.

 

[bobbiecool]

When solar panels are connected in series, voltage is additive current is not. So, 12 panels in series makes a little less than 300 volts which is comfortably in the range of the device they are attached to. But six in series do not reach the minimum voltage of that device. If they were reconfigured to 9 in each string you would have 220 volts per string and both strings would then be within the range of voltage required by the mppt.
Each string is running at 17 amps. The maximum input current of the device they are attached to is 12 amps. 17 is greater than 12.

Edit - pretty basic stuff that paid installer should know.

Thanks for that. The installation report was produced by the Easy PV program, I would have assumed it would have red flagged the inputs? Or maybe not...