Why monitor voltage?


just wondering why you monitor voltage especially AC?

i was thinking if i could monitor DC voltage for each string i can see if its getting shaded or of there seems to be an issue with a panel (not sure what else you can get from the dc voltage)

what can you learn/diagnose with ac voltage?
anything else you can learn/diagnose with DC voltage?


AC Voltages are typically measured at the main service panel. Since the capacity of your Utility Service is so significantly larger than a typical inverter, the voltage measured is almost completely driven by the the voltage delivered by the Utility. Therefor AC Voltage measurements provide info on the your Utility Service rather than your PV System. This could be helpful information if your inverter is going off line due to voltages outside it’s operating range.

While monitoring the DC Voltage of a string can be helpful, typical current monitoring is more useful. Utility scale systems will monitor both current and voltage and compare the values to IV curves provided by the manufacturer to determine if there are issues with the panels but this is not typical for residential systems.

I do monitor AC System voltage on my system but that’s basically a side benefit of the equipment I use to measure consumption.


Monitoring the DC will depend a bit on where the reading is from, at the panels the readings are more stable (using a multi meter), but from the inverter it show DC dancing around a lot as its converting that to AC, the more amps it can convert the more the DC readings change (this is the DC reading from the inverter not with a multimeter at the terminals)


B-man you have a fronius inverter??? if so just read the DC voltage straight of the inverter


yeah i guess i can thought it might be interesting to see the data corresponding to when it gets shading but its not something im going to look at once the fun wears off. or does it ever :joy:

yeah i do. as above post it doesn’t sound like Im going to get anything decent from the readings anyway


well with the DC voltage of a string and the amps at the same time,and with the output amps and AC voltage all from the same screen on Fronius solar web, history tab you can work out the overall Efficiency of your system


The overall efficiency could also be computed from Power Input (aka PV power) and Power Output. Most inverters are capable of show those two measurements already computed (with voltage and amps you compute power than compute efficiency).

I think logging DC can tell you when something happen to block light into your panels. While DC readings do swing, the swing under load is somewhat in a ball park. For instance, one of my arrays swings in between 340 and 370 volts under load. This swing depends on the quality/quantity of light hitting panels, load (from inverter), temperature (de-rating panels), etc. But, in a sunny day with few clouds, if a cloud pass between direct sunlight and panels I can see a huge drop outside the ballpark (like 250V for some minutes). In a very very hot day, the swing range shift downs a dozen volts or shift up in a cold winter day (very rare here I must say). What I want to say is that swing in DC volts will not invalidate its readings. On the other hand, monitoring AC voltage is very very stable, here, a 220V AC will vary from 219 to 223 with very few occasions of 217V, all variations inside range proposed by regulatory agencies. No surprise at all.

In my case I am logging DC voltage on standard voltage register and AC voltage on extended register. I did the opposite at first but for me it is meaningful to see string voltage alongside generation/power quantities and AC voltage on the other page at pvoutput. - my 2 cents



i have found the fronius solar web can graph that so i haven’t bothered doing anything about it i might just keep it located there for interest sake


i have found my inverter seems to limit its power (error “state 567”) when the voltage goes over 250 volts and seems to be happening quite a bit. and it’s only winter!
Does anyone else have this issue?


Hi B -man have a read of this,


i actually read that atricle a few days ago.

just wondering if others have the issue, how bad it is and what they have done to fix it?

mine not too bad at the moment but like i said its winter. and i can see it dropping off multiple times a day. im dreading summer


so if you read it what do you not understand about geting yours fixed??


First if you noticed i said if it goes over 250v. it hasn’t hit 255 or above yet so i

trying to find out what others have done.
ie ring distributor or Provider, or solar installer
What their response was, got told to deal with it or something actually happened?
is it worse in summer?
Does it actually affect it much? a few times over 250 isnt probably going to do much but if it’s hitting it now then its only going to get worse.


well it will get worse,mine derated to 4.2kw from 5kw last summer at 253v and shut off the inverter at 258v completely , so no solar output at all, inverter would not reconnect above 255v,so a big loss in solar power for my system, rang my solar installer and they said they would contact western power to get permission to raise my inverter output volts to 258v,this was done in a week which made the problem slightly less but did not fix it altogether, so i rang western power faults line and put in a overvoltage report, 3 line techs came out the next day to check it out and agreed with me it was overvoltage, i am last on a long supply line, so they said the would return soon and replace my overhead supply line was 6mm sq and 35 years old with a new 19 mm sq line this was done 4 days later, i still had over voltage problems so too engineers came out for the day to run tests and check for volts sag,there was lots so said they would need to put recording gear at my supply pole for a min of too weeks to make a case for major upgrade work to be done, thats a $100.000 + job due to the length of the line, well thats now been done and the line voltage at max output from my inverter has droped 8 volts so no more derating for me, as a result i think my system will output about another 1000 kw this year.
your installer can apply to change the inverter up to 258v in south austrlia if he askes the power company first for permission


great thanks for the informative information.

looking at my logs today i have had it creep up to 253volts for about 15 minutes around 2pm

looks like i will try contacting SA power when it starts hitting 255. as my solar installer said happens to everyone and there’s nothing you can do. he rang another bloke that confirmed it. so im at a loss there.