Hellboy0
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Depends on latitude.
The south of the UK receives from about 200 W/m2 on an overcast day to 1.3 KW/m2 in full sun. A minimum worthwhile installation is about 10m2. A typical cell is 8-10% efficient although some new technologies have raised this to as high as 40%
As an approximation a typical panel on a south facing roof will generate 120Kwh per square metre per year. A household may use 3000-5000 Kwh per year so would need 25-40 m2 at least to be self sufficient.
Typical payback on an average installation cost of at least £10000 and a use of 4000 Kwh per annum is thus about 35 years - far longer than the lifespan of current systems and 5 times the typical period a home is owned. There's simply no incentive for most people at present. The payback time estimates have been hotly debated with some quoting periods of over 45 years, back in 2005.
As volumes increase, prices will fall but it's got some way to go before it's mainstream, even allowing for grants. But I think it will happen, eventually and especially when it's built into new houses as standard.
What about wind power in your area? As for solar, crap, here in the Southern Hemisphere (back me up, Rugbypup), passive and electrical systems are extremely practical!!!! One of the big disincentives, though, is that the costs are high and the government gives crap rebates... hopefully the new Rudd government will make the difference that the Head-In-The-Sand Liberals wouldn't!