Sorry but isn't 'UK' and 'solar installation' an odd couple? My perception, based upon 40 years of western media consumption is that it's hardly sunny in the UK. I'm ready to be corrected though :)
A ~4kW installation gives me up to ~25kWh on a good day in summer. The big factor is actually the precession of the seasons since I'm at 56 degrees north. Retail electricity prices are now over 30p a kWh, so anything you can do to offset that is very useful.
Solar is pretty popular in the UK. Panels have reduced in cost per watt and energy bills have increased so much that it makes it worthwhile for many homes and businesses.
We do get the occasional sunny day contrary to popular belief, but even on cloudy days it's possible to generate a decent amount of energy.
We also have very long days in summer which can make for a decent amount of kWh/day (although the opposite is true in winter)
Annual sunshine is around 1300 hours in Glasgow, 1400 hours in Manchester, 1500 hours in Birmingham, 1700 hours in London and Paris, 2500 hours in Rome and 3500 hours in Cairo.
So it's not so sunny, especially as you go north, but films/TV do exaggerate the problem. "I'm from London" regularly gets a comment about terrible weather, "I'm from Paris" does not.
There is definitely an ROI, especially with recent prices (current tariffs are around 33p kWh)
Then there's the likes of Ripple Energy's solar park co-op offering. The levelised cost of buying in is around 2.5p kWh, with another 2p kWh going on maintenance. The return on the 1st (and active) co-op agreement there via a wind farm is 28p kWh, no reason why the solar park would give different returns than the wind one. Here in the UK grid pricing is more or less the same nationally.
Unfortunately there's much less of a return in Winter months due to higher latitudes, though in Summertime the days are longer than in many other countries.
Solar isn't an area I'm that familiar with but we have no issues generating plenty of electricity from the sun in the UK.
There's a great site [1] that calculates total solar generation around the UK using a mix of real data and forecasts. We were generating at 5GW around midday and that number will only increase.
