Low Solar readings

Yoshii

Hi there is a little bit of shading but only towards after 1pm but just for a small section and now all leaves have been blown off . I will keep eye on it.

Andy_WSM

Yoshii wrote: »

Hi there is a little bit of shading but only towards after 1pm but just for a small section and now all leaves have been blown off . I will keep eye on it.

ANY shading will have a huge impact. The panels are connected in series. If you lose 10% of one panel to shade, you lose 10% of the total output.

Cardew

Andy_WSM wrote: »

ANY shading will have a huge impact. The panels are connected in series. If you lose 10% of one panel to shade, you lose 10% of the total output.

It is my understanding that the effect can be more dramatic than you state.


If you Google 'shading effect on PV installations' there are many results from those for the Layman to highly technical.


http://www.yougen.co.uk/blog-entry/1627/Shading+has+more+impact+on+solar+PV+than+orientation+or+pitch/

On one occasion a 15% level of shading on an array reduced the output to less than 5% of what would otherwise be expected.

System

Just to back that up. I purchased a PV array knowing that for up to an hour each day the top of a 100ft fir tree would throw a shadow over a small part of the array. My installer carried out a detailed analysis which showed a massive PV loss in the winter months and only a small loss from Apr thro' to Sep. The total loss was estimated at c.20% for the year. Fortunately, after the first year, my neighbour cut down the tree to make room for a new build garage. My annual PV output has risen from about 1730 to 1940 Kwhs per annum.

Andy_WSM

Cardew wrote: »

It is my understanding that the effect can be more dramatic than you state.


If you Google 'shading effect on PV installations' there are many results from those for the Layman to highly technical.


http://www.yougen.co.uk/blog-entry/1627/Shading+has+more+impact+on+solar+PV+than+orientation+or+pitch/

Yes, can be. Some panels have bypass diodes, some inverters have smart trackers. Don't really know what's at play here, but as I said earlier, any shading is to be avoided and it sounds like that could well be the issue here.

Martyn1981

Andy_WSM wrote: »

ANY shading will have a huge impact. The panels are connected in series. If you lose 10% of one panel to shade, you lose 10% of the total output.

Yes and no.

If a whole row or column of cells is shaded, then you could lose the whole panel. The drag from that panel could pull the whole system down by up to 50%. (Edit: Apologies, whole string. M.]

However, that's a worst case scenario, as you say:

Andy_WSM wrote: »

Yes, can be. Some panels have bypass diodes, some inverters have smart trackers. Don't really know what's at play here, but as I said earlier, any shading is to be avoided and it sounds like that could well be the issue here.

Looking at my ESE systems, they have,
SMA inverters but not high efficiency models,
neither has Optritrac Global Peak,
both systems single strings,
the smaller system gets some shading from a tree in the bottom months,
the smaller system gets shading from the upper roof as the afternoon goes on,
the upper system gets 'hard' shading from a southern chimney (my house is the northern half of a semi, with a large central chimney).

When installed I hoped for 80 to 90% of PVGIS target each year. So far I've got:
2011 (part year and part month) 98%
2012 99%
2013 102%
2014 past annual target already and projecting 108%

I should add that my WNW system has more shading, but has SolarEdge tech, and consistently outperforms the ESE (when orientation is taken into account).

I'd never underestimate shading, and Yoshii really needs to give us more to go on, but the figures so far, for a good day, in late August/early Sept are only 20 to 25% of what should/could be expected. [I'm working on a good day being 20 to 26kWh, assuming 4kWp and south(ish) facing.]

Without wishing to be rude to Yoshii, if he/she has that much shading, pretty much all day, then it should be blindingly (excuse the pun) obvious. Especially given the statement

Yoshii wrote: »

Hi
Over the past 2 months my 4kwh solar system has been giving readings of 1-1.3kwh even in full direct sunshine ...

The lack of actual follow up data, and the slightly confused info given so far, makes me wonder what exactly is going on here?

Edit: Just to add @Yoshii, when you say all leaves blown off it, are you referring to a tree? Shading from a tree can be a right pig, but still doesn't explain why gen before 1pm isn't already greater than 6kWh on a good summer day. M.

Mart.

Yoshii

Cardew wrote: »

Agree with the above - shading is the first thing to suspect.


What was the readings in June/July?

My output in june was 420 kwh

and in Jul it was 490kwh.

I have 6 panels ESE and 10 panels on opposite side of pitched roof. The shading from the trees i have now realised does cast a shadow over the 1/2 of the 6 panel ESE side. Should I call the installers to check it out?

Yoshii

re the leaves getting blown off...I meant that with the windy weather over the past few days alotof leaves have been blown off the offending(shading) tree. Maybe this will help generate more kwh?

Martyn1981

Yoshii wrote: »

My output in june was 420 kwh

and in Jul it was 490kwh.

I have 6 panels ESE and 10 panels on opposite side of pitched roof. The shading from the trees i have now realised does cast a shadow over the 1/2 of the 6 panel ESE side. Should I call the installers to check it out?

Hiya Yoshii, that sounds like generation in June and July was ok. What was total generation for August and September? Your 4-6kWh max statement suggests generation has fallen off a cliff.

So it's a split system, that's the crucial bit of info that was missing. This is why I asked right back at the start if it was a split system as this complicates matters, and makes any guestimate of generation much harder.

When you say the 10 panels are on the opposite pitch to the ESE, does that mean (like me) they are on a WNW roof? If so, what is the roof pitch? As this will have more of an effect on a non south facing roof as we move(d) from summer to autumn.

If the tree shading the ESE only affects it after 1pm, does that mean the tree is to the south, or is it further to the south west, potentially impacting the WNW roof too? Or are you now saying it shades the ESE before 1pm?

Solutions: Well, still need to clarify performance in the last 2 months, but can you say what inverter you have (make and model), it may be that your current set up (with a split shaded system) isn't suitable?

When was the system installed? Is this your first autumn with it? It may be that the system needs a better inverter, or micro-inverters/SolarEdge system. Do you think your installer would be open to reviewing it and consider an upgrade?

Mart.

Yoshii

yes you are correct in that the other 10 panels face WNW.

inverter is SMA 4000TL and Generation Meter is the ElsterA100C