There is a clever piece of software which I believe originated in Sweden 
that can calculate roofspace, elevation and shadow from trees from 3D 
surveys and hence solar potential.
Southampton University have done this survey and conclude that 40% of 
the city's electricity could be supplied by solar.
The trouble is it is very expensive to cover thousands of small 
individual sites whereas a large site is much easier to build and so 
much cheaper. I agree that it is much preferable to use existing roofs 
but there are many reasons why owners cant or dont want to.
At Lymington, the solar farm was built on an old landfill site and is 
managed by the Hants Wildlife trust to encourage wildlife and improve 
the land. The mounting systems use only about 3% of the site and can be 
removed completely.
Renewables are the only tools that we have to avoid catastrophic climate 
change which would be very intrusive indeed.
Roger
On 12/11/15 15:04, Gordon Scott wrote:
> Whilst I approve of PV in principle, I do wish they'd put them in places
> that aren't additionally intrusive into the environment.
>
> Put them over supermarket and other car parks, giving shade to the cars
> as well. Factory, supermarket and shopping-centre roofs, bus shelters,
> railway station roofs, etc..
>
> Why oh why do they so often put them in green spaces?  It's ridiculous.
>
>
> Gordon.
>
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