Shading issues on PV array

[noidea]

Evening all
I work for a firm in Kent installing PV systems on mainly domestic properties.
We have just finished installing a 1.8kw system.
The problem is that there are major issues with shading from the neighbours roof. The sun only comes out from behind the roof fully at around 3 o'clock, when it then goes behind some trees. (poor selling and planning I know, but go with it)
The highest reading we got today was 250watts. The customer is not overly concerned as the sun will be higher in the summer (more money than sense)
I understand that shading is a major issue with PV, so my question is, how much shading can a PV system cope with before it becomes a problem?

(Apologies if this has apperared twice, I had problems when submitting the thread)

 

[SRE]

PVSol calculates this for you but I'd have real problems with an installation that has no sun until 3 even if it's in the Winter. Shading has a major impact on the performance of the panels, you can route your strings to avoid the shading or use microinverters (loads more expensive but only reduce output on the panels in shade rather than the whole string.) Even slight shading can reduce system efficiency by 25%

 

[yellowvanman]

If you have shading on just 1 panel (or even a small part of 1 panel) that could greatly effect the whole output.

Try this experiment and see. Get a panel and short ciruit the outputs, measure the current on a nice bright day, then get a blanket (or similar) and place it along a small section of the panel, you will see the current dramatically reduced - even by as much as 75%.

If you've got 1 string with all the panels in series this shaded panel is affecting all the others!