Photovoltaic solar cells- a no brainer?

Wonny for clarity do you mean LCC or LCA? if LCA there’s sufficient data within some of the LCA applications (eg simapro) to undertake an analysis as you can buildup composite values which would get you close to most of the components,.
These kind of assements get more interesting when you include the through life implications of the energy used/ displaced, capital replacement, maintenance and run them out to the life of the structure theyre attached to 60yr +

although PV is a useful technology there’s a shortage of real world data + a lot of sales based data out there

sorry to dig this up, were close to pushing the button on a 4kw 16 panel system… one question we can’t get a straight answer on is shading. The roof faces 5 degrees off south, but to the south west side our neighbor has a silver birch that shades part of our roof in the afternoon, from about 4 ish onwards.. is a tree considered as shading in terms of output from the panels ?

Yes. Trees are a problem for shading, even in winter with just branches.

Yes it is. Anything that gets in the way of teh sun reaching your panels is shading. Do you have any say over the tree or will it be allowed to grow and shade even more of your panel site?

I can trim it off flat on my side.. and had a word with the neighbor before to keep it down, its always been a bit of a bug bear between us… mmmm, give this some thought.

Hopefully your quote will have provided you with a SAP derived prediction of annual system output. This should have accounted for the shading in such general, overly-cautious terms that I would be very surprised if performance was hammered to the extent the SAP rating predicts (assuming it was indeed accounted for. If not, choose another supplier).

Modelling ‘soft’ shading issues such as that from trees, where a variable amount of light can pass through is very difficult. However, from real world experience I have been quite surprised how little the effects of shading actually do impact on system performance. For example, I tested an 18 panel system recently, split into two strings of 9 panels. One string had 4 panels heavily shaded by a chimney. It was a bright sunny day when I carried out the tests and the shading was obvious. However, both strings (the other being completely unshaded) were performing identically. Surprised me.

Also bear that there is plenty of diffuse light falling on panels most of the time (especially in the UK default weather setting of ‘overcast’), so even if the sun is hidden behind a tree, light will still be reaching the system and performance may not be affected too much.

Sorry, I’m waffling. No easy answer. However, it is important that your chosen system supplier has recognized and accounted for the shading issues. If not, find someone else.

Dudie, thanks very much for the very very informative reply.