Renewables: "talking 'bout my generation"

Ferdy147

Anybody got any ideas on this one? Is something wrong or is it within normal variance?

We had 2 systems installed in Feb - Both identical (3.92kw suntech panels in 8*2 configuration and Sunnyboy 4000tl inverter).The systems are on my parents and sisters house which are next door to each other and neither has ANY shading. .

In the first month the reading from both systems were pretty much the same. If anything, the system on my sisters house was slightly higher for Feb/March than my parents. Since then my sisters house is producing noticably less than my parents - say 10% less when you look at the inverter or generation meter readings.

Is there something that needs to be looked at or is that kind of difference to be expected?

EricMears

Ferdy147 wrote: »

Anybody got any ideas on this one? Is something wrong or is it within normal variance?

We had 2 systems installed in Feb - Both identical (3.92kw suntech panels in 8*2 configuration and Sunnyboy 4000tl inverter).The systems are on my parents and sisters house which are next door to each other and neither has ANY shading. .

In the first month the reading from both systems were pretty much the same. If anything, the system on my sisters house was slightly higher for Feb/March than my parents. Since then my sisters house is producing noticably less than my parents - say 10% less when you look at the inverter or generation meter readings.

Is there something that needs to be looked at or is that kind of difference to be expected?

A difference in slope of roof might have that sort of effect - though if they're next door neighbours there's every chance they'll have same shaped rooves.

NO shading at all ?? Not even a chimney stack ? There would be a noticeable difference in shading from a stack between (say) a left hand semi and a right hand semi.

If none of above, then maybe bird excrement on one of panels could be the culprit ?

Ferdy147

Both houses are detatched and originally the same although the parent's has now been extended. The roof will be the same angle and both are south facing. The chimney is on the other side of the roof so I don't think that would cause shading....although looking at the streetview just now I can see the TV ariel may cause some shading.... But both houses have ariels in the same place. Could that be the reason....they're coming off if they are! Nobody uses the terrestial feed anyway lol.

Martyn1981

Ferdy147 wrote: »

Anybody got any ideas on this one? Is something wrong or is it within normal variance?

Is there something that needs to be looked at or is that kind of difference to be expected?

Ferdy, annoyingly, I'd say that a 10% difference on two identical installs next door to each other is big enough to warrant investigation.

Eric beat me to it with the two sensible solutions, so here's some daft ones.

AC Cables, on large systems like those, if the cables are small (2.5mm) then they might reduce generation a bit - but I assume both installs were by the same company (?) so unlikely they'd have varied their install method.

Panel performance, most panels have a +/- or +/0 variance. But again astonishing 'luck' for one house to get the better panels and one the lesser, plus doesn't explain the reversal since Feb.

TGM accuracy, these are just import meters and as such have (I believe) a tolerance of 1% over, and 2% under, but as above, very unlikely explanation.

Local overvoltage problem, causing intermittent system shutdowns on the SB4000TL's, but surely would affect both houses the same if next door.

Duff panel in one of the strings, never really played with this stuff, but the inverter should tell you the voltages on both strings, so see if they are pretty much the same, or if one string is under performing. You might even be able to compare the voltages from the two houses.

Call the installer if the difference continues and you can't see anything obvious.

Mart.

Ferdy147

Thanks for both your replies guys. Yes both were installed by the same company and when we took delivery of the kit it was all from the same place and same delivery so I'd assume there's no difference in the components.

Will check the string voltage when I'm back home at the weekend and see if there's anything noticeable there. As you say the performance reversal is odd as it was originally the parents house that was causing the concern (Feb wasn't a great month but on the one day of sunshine my sister's did 17.xkw and my parents 14.xkw).

Overall I'm quite happy with the figure's, had there not have been one next door to compare with I wouldn't have thought anything was wrong. As of this morning my parents meter reading was 2050 and my sisters I imagine was probably about 1900. Both systems were complete on the same day - 9th Feb - so not yet 6 months and the weather hasn't been great so I'm quite happy with the numbers so far.

Martyn1981

Hiya Ferdy, popped back on as another idea occurred to me, but again a very odd long shot. Could the inverters have been set up differently? Highly unlikely if the same company, and possibly the same spark, but you never know.

I don't know exactly how they can differ, I just know that they can (if that makes sense, like I know a car can be tuned differently, but I wouldn't know how too). MPPT check times can be changed, system set-ups can differ, MPPT modes etc etc. The inverters can even be !!!!!! (in 1W increments), or one 4000 may be 3.68 capped and the other slipped through (not set to G83). I can't imagine that these would account for the difference you and yours have noticed, but food for thought perhaps.

Best of luck, and you will let us know what you find won't you (and by us I of course mean 'nosey Mart').

Mart.

Ferdy147

OK I'll check the settings that I can see on Sunny Explorer and see if there's any noticeable difference. I had wondered whether a reboot was in order...normally an IT support fix!

Connecting to the inverters via Sunny Explorer/Bluetooth isn't always possible in both houses. The bluetooth transmission seems to be intermittent although looking at the day generation graphs it's not the whole inverter that's shutting down. I just keep trying and eventually it connects...

Do you think shading caused by the TV ariel could affect output? I guess it'd be the same for both houses but as neither use terrestial feeds there's no need for them. Could that be a significant amount or negligible would you say?

Of course will let you know of any findings!

sly_dog_jonah

Ferdy147 wrote: »

OK I'll check the settings that I can see on Sunny Explorer and see if there's any noticeable difference. I had wondered whether a reboot was in order...normally an IT support fix!

Connecting to the inverters via Sunny Explorer/Bluetooth isn't always possible in both houses. The bluetooth transmission seems to be intermittent although looking at the day generation graphs it's not the whole inverter that's shutting down. I just keep trying and eventually it connects...

Do you think shading caused by the TV ariel could affect output? I guess it'd be the same for both houses but as neither use terrestial feeds there's no need for them. Could that be a significant amount or negligible would you say?

Of course will let you know of any findings!

TV Aerials, or any seemingly small object casting a shadow, can have a dramatic effect on a PV system. The reason is that the shading not only affects the output of the shaded panel, it can also affect the performance of other panels on the same 'string'. It's pretty complicated how an inverter works, but in simplified terms the worst panel pulls down the output of all the other panels which the inverter tracks together.

Aside: We had to get our TV aerial moved from within the loft to a chimney stack last week. The aerial in it's original position was suffering from poor reception due to the fact that it was pointing right 'through' the PV array on our roof towards the Mendip TV transmitter. The metal and foil backing of the panels is a pretty good reflector of TV signals. First we had it moved to the end of the loft, but even though that meant we could then pick up a full strength signal on all multiplexes (including HD which was previously too weak) we were still suffering from freezes on various channels, due to signal quality hovering around the 4-6/10 on various channels.

Not wanting to miss any critical bits of the Olympics, we had it moved to the roof and now get a perfect 10 on signal strength and more importantly 9/10 on signal quality. Fortunately we had two (faux) chimneys to choose from, so had it positioned on the East chimney so that it wouldn't ever cast a shadow on the (ESE) panels. Just to be on the safe side we had the pole mounted on the north side of the chimney to minimise the risk even more (since the aerial has to point south).

Probably best illustrated with a photo, I'll update this post shortly.

Edit:

John_Pierpoint

I am glad you have found a use for the "faux" chimney:D

sly_dog_jonah

John_Pierpoint wrote: »

I am glad you have found a use for the "faux" chimney:D

Yeah, a bit of a pointless 'feature' of the housebuilder's design. 4 of the 5 house designs on our development have them. Ironically one house has had a stainless steel chimney installed running up the outside of their house so they could have a wood-burning stove in their lounge.